# TinkerPop Upgrade Information

This document helps users of TinkerPop to understand the changes that come with each software release. It outlines new features, how to resolve breaking changes and other information specific to a release. This document is useful to end-users who are building applications on TinkerPop, but it is equally useful to TinkerPop providers, who build libraries and other systems on the core APIs and protocols that TinkerPop exposes.

These providers include:

- Graph System Provider

  - Graph Database Provider

  - Graph Processor Provider

- Graph Driver Provider

- Graph Language Provider

- Graph Plugin Provider

# TinkerPop 3.2.0

Nine Inch Gremlins

## TinkerPop 3.2.11

Release Date: January 2, 2019

Please see the changelog for a complete list of all the modifications that are part of this release.

## TinkerPop 3.2.10

Release Date: October 15, 2018

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### SASL in Gremlin.Net

The Gremlin Javascript Driver now supports SASL Plain Text authentication against a Gremlin Server.

See: TINKERPOP-1977, Reference Documentation - Gremlin Javascript

#### SSL Security

TinkerPop improves its security posture by removing insecure defaults and adding forward-looking standards support.

Gremlin Server no longer supports automatically creating self-signed certificates. Self-signed certificates can still be created manually outside of Gremlin Server. If ssl is enabled, a key store must be configured.

Cluster client no longer trusts all certs by default as this is an insecure configuration. Instead, if no trust store is configured, Cluster will use the default CA certs. To revert to the previous behavior and accept all certs, it must be explicitly configured.

This release introduces JKS and PKCS12 support. JKS is the legacy Java Key Store. PKCS12 has better cross-platform support and is gaining in adoption. Be aware that JKS is the default on Java 8. Java 9 and higher use PKCS12 as the default. Both Java keytool and OpenSSL tools can create, read, update PKCS12 files.

Other new features include specifying SSL protocols and cipher suites. The packaged `*-secure.yaml` files now restrict the protocol to `TLSv1.2` by default.

PEM-based configurations are deprecated and may be removed in a future release.

See also Connecting via Java Configuration, Gremlin Server Configuration.

TINKERPOP-2022 TINKERPOP-2023

#### Bulk Import and Export

TinkerPop has provided some general methods for importing and exporting data, but more and more graph providers are producing their own bulk import/export facilities and they are more efficient and easier to use than TinkerPop’s methods. As a result, TinkerPop will now refer users to the bulk import/export features of individual graph providers and as such, has deprecated `BulkLoaderVertexProgram` as of this release.

As part of this change, the `BulkDumperVertexProgram` has been renamed to `CloneVertexProgram` with the former being deprecated. `CloneVertexProgram` is more aptly named, as it essentially copies a graph from a graph `InputFormat` to a graph `OutputFormat`.

TINKERPOP-1985

#### Docker Images

Docker images are now available on Docker Hub for Gremlin Console and Gremlin Server.

    $ docker run -it tinkerpop/gremlin-console:3.2.11
    $ docker run tinkerpop/gremlin-server:3.2.11

See: TINKERPOP-1897, Reference Documentation - Gremlin Console, Reference Documentation - Gremlin Server,

#### TimedInterruptCustomizerProvider

In Gremlin Server, it is best not to use {{TimedInterruptCustomizerProvider}} because it can compete with the {{scriptEvaluationTimeout}} setting and produce a different error path. Simply rely on {{scriptEvaluationTimeout}} as it covers both script evaluation time and result iteration time.

See: TINKERPOP-1778

#### TinkerFactory.createGratefulDead()

The Grateful Dead dataset has been with TinkerPop since the early days of 1.x. It has always been available as a packaged dataset that needed to be loaded through the various IO options available, while other toy graphs had the benefit of `TinkerFactory` to help get them bootstrapped. For 3.2.10, Grateful Dead is now more conveniently loaded via that same method as the other toy graphs with `TinkerFactory.createGratefulDead()`.

#### Gremlin Javascript Script Submission

Gremlin Javascript can now submit script, with optional bindings, using the `Client` class:

    const gremlin = require('gremlin');
    const connection = new gremlin.driver.Client('ws://localhost:8182/gremlin', { traversalSource: 'g' });

    connection.submit('g.V().tail()')
        .then(response => {
            console.log(response.traversers.length);
            console.log(response.traversers[0]);
        });

    connection.submit('g.V(vid)', {vid: 1})
        .then(response => {
            console.log(response.traversers.length);
            console.log(response.traversers[0]);
        });

and also allows translation of bytecode steps into script:

    const gremlin = require('gremlin');
    const graph = new gremlin.process.Graph();
    const connection = new gremlin.driver.Client('ws://localhost:8182/gremlin', { traversalSource: 'g' });
    const translator = new gremlin.process.Translator('g');

    const g = graph.traversal();
    const script = translator.translate(g.V().tail().getBytecode());

    connection.submit(script)
        .then(response => {
            console.log(response.traversers.length);
            console.log(response.traversers[0]);
        });

### Upgrading for Providers

#### Graph Database Providers

##### Bulk Import and Export

As noted in the user section, TinkerPop has deprecated its bulk loading feature in `BulkLoaderVertexProgram` and will refer TinkerPop users who need bulk import/export capabilities to the native tools of the graph database they have chosen. If a graph database provider does not have any bulk loading tools it can choose to build graph `InputFormat` and `OutputFormat` implementations which can be used by `CloneVertexProgram` (formerly `BulkDumperVertexProgram`) as a easy way to get such a feature.

TINKERPOP-1985

## TinkerPop 3.2.9

Release Date: May 8, 2018

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Lambda Construction

It was realized quite shortly after release of 3.2.8 that there was a bug in construction of `Lambda` instances:

    gremlin> org.apache.tinkerpop.gremlin.util.function.Lambda.function("{ it.get() }")
    (class: org/apache/tinkerpop/gremlin/util/function/Lambda$function, method: callStatic signature: (Ljava/lang/Class;[Ljava/lang/Object;)Ljava/lang/Object;) Illegal type in constant pool
    Type ':help' or ':h' for help.
    Display stack trace? [yN]n

The problem was related to a bug in Groovy 2.4.14 and was fixed in 2.4.15.

See: TINKERPOP-1953

## TinkerPop 3.2.8

Release Date: April 2, 2018

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Improved Connection Monitoring

Gremlin Server now has two new settings: `idleConnectionTimeout` and `keepAliveInterval`. The `keepAliveInterval` tells Gremlin Server how long it should wait between writes to a client before it issues a "ping" to that client to see if it is still present. The `idleConnectionTimeout` represents how long Gremlin Server should wait between requests from a client before it closes the connection on the server side. By default, these two configurations are set to zero, meaning that they are both disabled.

This change should help to alleviate issues where connections are left open on the server longer than they should be by clients that might mysteriously disappear without properly closing their connections.

See: TINKERPOP-1726

#### Gremlin.Net Lambdas

Gremlin.Net now has a `Lambda` class that can be used to construct Groovy or Java lambdas which will be evaluated on the server.

See: TINKERPOP-1854, Reference Documentation - Gremlin.Net - The Lambda Solution.

#### Gremlin.Net Tokens Improved

The various Gremlin tokens (e.g. `T`, `Order`, `Operator`, etc.) that were implemented as Enums before in Gremlin.Net are now implemented as classes. This mainly allows them to implement interfaces which their Java counterparts already did. `T` for example now implements the new interface `IFunction` which simply mirrors its Java counterpart `Function`. Steps that expect objects for those interfaces as arguments now explicitly use the interface. Before, they used just `object` as the type for these arguments which made it hard for users to know what kind of `object` they can use. However, usage of these tokens themselves shouldn’t change at all (e.g. `T.Id` is still `T.Id`).

See: TINKERPOP-1901

#### Gremlin.Net: Traversal Predicate Classes Merged

Gremlin.Net used two classes for traversal predicates: `P` and `TraversalPredicate`. Steps that worked with traversal predicates expected objects of type `TraversalPredicate`, but they were constructed from the `P` class (e.g. `P.Gt(1)` returned a `TraversalPredicate`). Merging these two classes into the `P` class should avoid unnecessary confusion. Most users should not notice this change as predicates can still be constructed exactly as before, e.g., `P.Gt(1).And(P.Lt(3))` still works without any modifications. Only users that implemented their own predicates and used `TraversalPredicate` as the base class need to change their implementation to now use `P` as the new base class.

See: TINKERPOP-1919

### Upgrading for Providers

#### Graph System Providers

##### Kitchen Sink Test Graph

The "Kitchen Sink" test graph has been added to the `gremlin-test` module. It contains (or will contain) various disconnected subgraphs of that offer unique structures (e.g. a self-loop) for specific test cases. Graph systems that use the test suite should not have to make any changes to account for this new graph unless that system performs some form or special pre-initialization of their system in preparation for loading (e.g. requires a schema) or does the loading of the graph test data outside of the standard method in which TinkerPop provides.

See: TINKERPOP-1877

## TinkerPop 3.2.7

Release Date: December 17, 2017

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Gremlin-Python Core Types

With the addition of `UUID`, `Date`, and `Timestamp`, Gremlin-Python now implements serializers for all core GraphSON types. Users that were using other types to represent this data can now use the Python classes `datetime.datetime` and`uuid.UUID` in GLV traversals. Since Python does not support a native `Timestamp` object, Gremlin-Python now offers a dummy class `Timestamp`, which allows users to wrap a float and submit it to the Gremlin Server as a `Timestamp` GraphSON type. `Timestamp` can be found in `gremlin_python.statics`.

See: TINKERPOP-1807

#### EventStrategy Detachment

`EventStrategy` forced detachment of mutated elements prior to raising them in events. While this was a desired outcome, it may not have always fit every use case. For example, a user may have wanted a reference element or the actual element itself. As a result, `EventStrategy` has changed to allow it to be constructed with a `detach()` option, where it is possible to specify any of the following: `null` for no detachment, `DetachedFactory` for the original behavior, and `ReferenceFactory` for detachment that returns reference elements.

See: TINKERPOP-1829

#### Embedded Remote Connection

As Gremlin Language Variants (GLVs) expand their usage and use of `withRemote()` becomes more common, the need to mock the "remote" in unit tests increases. To simplify mocking in Java, the new `EmbeddedRemoteConnection` provides a simple way to provide a "remote" that is actually local to the same JVM.

See: TINKERPOP-1756

#### DSL Type Specification

Prior to this version, the Java annotation processor for Gremlin DSLs has tried to infer the appropriate type specifications when generating anonymous methods. It largely performed this inference on simple conventions in the DSL method’s template specification and there were times where it would fail. For example, a method like this:

    public default GraphTraversal<S, E> person() {
        return hasLabel("person");
    }

would generate an anonymous method like:

    public static <S> SocialGraphTraversal<S, E> person() {
        return hasLabel("person");
    }

and, of course, generate a compile error and `E` was not recognized as a symbol. The preferred generation would likely be:

    public static <S> SocialGraphTraversal<S, S> person() {
        return hasLabel("person");
    }

To remedy this situation, a new annotation has been added which allows the user to control the type specifications more directly providing a way to avoid/override the inference system:

    @GremlinDsl.AnonymousMethod(returnTypeParameters = {"A", "A"}, methodTypeParameters = {"A"})
    public default GraphTraversal<S, E> person() {
        return hasLabel("person");
    }

which will then generate:

    public static <A> SocialGraphTraversal<A, A> person() {
        return hasLabel("person");
    }

See: TINKERPOP-1791

#### Specify a Cluster Object

The `:remote connect` command can now take a pre-defined `Cluster` object as its argument as opposed to a YAML configuration file.

    gremlin> cluster = Cluster.open()
    ==>localhost/127.0.0.1:8182
    gremlin> :remote connect tinkerpop.server cluster
    ==>Configured localhost/127.0.0.1:8182

See: TINKERPOP-1787

#### Remote Traversal Timeout

There was limited support for "timeouts" with remote traversals (i.e. those traversals executed using the `withRemote()` option) prior to 3.2.7. Remote traversals will now interrupt on the server using the `scriptEvaluationTimeout` setting in the same way that normal script evaluations would. As a reminder, interruptions for traversals are always considered "attempts to interrupt" and may not always succeed (a graph database implementation might not respect the interruption, for example).

See: TINKERPOP-1770

#### Modifications to match()

The `match()`-step has been generalized to support the local scoping of all barrier steps, not just reducing barrier steps. Previously, the `order().limit()` clause would have worked globally yielding:

    gremlin> g.V().match(
    ......1>   __.as('a').outE('created').order().by('weight',decr).limit(1).inV().as('b'),
    ......2>   __.as('b').has('lang','java')
    ......3> ).select('a','b').by('name')
    ==>[a:marko,b:lop]

However, now, `order()` (and all other barriers) are treated as local computations to the pattern and thus, the result set is:

    gremlin> g.V().match(
    ......1>   __.as('a').outE('created').order().by('weight',decr).limit(1).inV().as('b'),
    ......2>   __.as('b').has('lang','java')
    ......3> ).select('a','b').by('name')
    ==>[a:marko,b:lop]
    ==>[a:josh,b:ripple]
    ==>[a:peter,b:lop]

Note that this is not that intense of a breaking change as all of the reducing barriers behaved in this manner previously. This includes steps like `count()`, `min()`, `max()`, `sum()`, `group()`, `groupCount()`, etc. This update has now generalized this behavior to all barriers and thus, adds `aggregate()`, `dedup()`, `range()`, `limit()`, `tail()`, and `order()` to the list of locally computed clauses.

See: TINKERPOP-1764

#### Clone a Graph

In `gremlin-test` there is a new `GraphHelper` class that has a `cloneElements()` method. It will clone elements from the first graph to the second - `GraphHelper.cloneElements(Graph original, Graph clone)`. This helper method is primarily intended for use in tests.

#### MutationListener Changes

The `MutationListener` has a method called `vertexPropertyChanged` which gathered callbacks when a property on a vertex was modified. The method had an incorrect signature though using `Property` instead of `VertexProperty`. The old method that used `Property` has now been deprecated and a new method added that uses `VertexProperty`. This new method has a default implementation that calls the old method, so this change should not cause breaks in compilation on upgrade. Internally, TinkerPop no longer calls the old method except by way of that proxy. Users who have `MutationListener` implementations can simply add the new method and override its behavior. The old method can thus be ignored completely.

See: TINKERPOP-1798

### Upgrading for Providers

#### Direction.BOTH Requires Duplication of Self-Edges

Prior to this release, there was no semantic check to determine whether a self-edge (e.g. `e[1][2-self→2]`) would be returned twice on a `BOTH`. The semantics have been specified now in the test suite where the edge should be returned twice as it is both an incoming edge and an outgoing edge.

See: TINKERPOP-1821

## TinkerPop 3.2.6

Release Date: August 21, 2017

### Upgrading for Users

Please see the changelog for a complete list of all the modifications that are part of this release.

#### Deprecated useMapperFromGraph

The `userMapperFromGraph` configuration option for the Gremlin Server serializers has been deprecated. Change configuration files to use the `ioRegistries` option instead. The `ioRegistries` option is not a new feature, but it has not been promoted as the primary way to add `IoRegistry` instances to serializers.

See: TINKERPOP-1694

#### WsAndHttpChannelizer

The `WsAndHttpChannelizer` has been added to allow for processing both WebSocket and HTTP requests on the same port and gremlin server. The `SaslAndHttpBasicAuthenticationHandler` has also been added to service authentication for both protocols in conjunction with the `SimpleAuthenticator`.

See: TINKERPOP-915

### Upgrading for Providers

#### ReferenceVertex Label

`ReferenceVertex.label()` was hard coded to return `EMPTY_STRING`. At some point, `ReferenceElements` were suppose to return labels and `ReferenceVertex` was never updated as such. Note that `ReferenceEdge` and `ReferenceVertexProperty` work as expected. However, given a general change at `ReferenceElement`, the Gryo serialization of `ReferenceXXX` is different. If the vertex does not have a label `Vertex.DEFAULT_LABEL` is assumed.

See: TINKERPOP-1789

## TinkerPop 3.2.5

Release Date: June 12, 2017

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### GraphSON Path Serialization

Serialization of `Path` with GraphSON was inconsistent with Gryo in that all the properties on any elements of the `Path` were being included. With Gryo that, correctly, was not happening as that could be extraordinarily expensive. GraphSON serialization has now been modified to properly not include properties. That change can cause breaks in application code if that application code tries to access properties on elements in a `Path` as they will no longer be there. Applications that require the properties will need to alter their Gremlin to better restrict the data they want to retrieve.

See: TINKERPOP-1676

#### DSL Support

It has always been possible to construct Domain Specific Languages (DSLs) with Gremlin, but the approach has required a somewhat deep understanding of the TinkerPop code base and it is not something that has had a recommended method for implementation. With this release, TinkerPop simplifies DSL development and provides the best practices for their implementation.

    // standard Gremlin
    g.V().hasLabel('person').
      where(outE("created").count().is(P.gte(2))).count()

    // the same traversal as above written as a DSL
    social.persons().where(createdAtLeast(2)).count()

See: TINKERPOP-786, Reference Documentation

#### Authentication Configuration

The server settings previously used `authentication.className` to set an authenticator for the the two provided authentication handler and channelizer classes to use. This has been deprecated in favor of `authentication.authenticator`. A class that extends `AbstractAuthenticationHandler` may also now be provided as `authentication.authenticationHandler` to be used in either of the provided channelizer classes to handle the provided authenticator

See: TINKERPOP-1657

#### Default Maximum Parameters

It was learned that compilation for scripts with large numbers of parameters is more expensive than those with less parameters. It therefore becomes possible to make some mistakes with how Gremlin Server is used. A new setting on the `StandardOpProcessor` and `SessionOpProcessor` called `maxParameters` controls the number of parameters that can be passed in on a request. This setting is defaulted to sixteen.

Users upgrading to this version may notice errors in their applications if they use more than sixteen parameters. To fix this problem simply reconfigure Gremlin Server with a configuration as follows:

    processors:
      - { className: org.apache.tinkerpop.gremlin.server.op.session.SessionOpProcessor, config: { maxParameters: 64 }}
      - { className: org.apache.tinkerpop.gremlin.server.op.standard.StandardOpProcessor, config: { maxParameters: 64 }}

The above configuration allows sixty-four parameters to be passed on each request.

See: TINKERPOP-1663

#### GremlinScriptEngine Metrics

The `GremlinScriptEngine` has a number of new metrics about its cache size and script compilation times which should be helpful in understanding usage problems. As `GremlinScriptEngine` instances are used in Gremlin Server these metrics are naturally exposed as part of the standard metrics set. Note that metrics are captured for both sessionless requests as well as for each individual session that is opened.

See: TINKERPOP-1644

#### Additional Error Information

Additional information on error responses from Gremlin Server should help make debugging errors easier. Error responses now have both the exception hierarchy and the stack trace that was generated on the server. In this way, receiving an error on a client doesn’t mean having to rifle through Gremlin Server logs to try to find the associated error.

This change has been applied to all Gremlin Server protocols. For the binary protocol and the Java driver this change means that the `ResponseException` thrown from calls to `submit()` requests to the server now have the following methods:

    public Optional<String> getRemoteStackTrace()

    public Optional<List<String>> getRemoteExceptionHierarchy()

The HTTP protocol has also been updated and returns both `exceptions` and `stackTrace` fields in the response:

    {
            "message": "Division by zero",
            "Exception-Class": "java.lang.ArithmeticException",
            "exceptions": ["java.lang.ArithmeticException"],
            "stackTrace": "java.lang.ArithmeticException: Division by zero\n\tat java.math.BigDecimal.divide(BigDecimal.java:1742)\n\tat org.codehaus.groovy.runtime.typehandling.BigDecimalMath.divideImpl(BigDecimalMath.java:68)\n\tat org.codehaus.groovy.runtime.typehandling.IntegerMath.divideImpl(IntegerMath.java:49)\n\tat org.codehaus.groovy.runtime.dgmimpl.NumberNumberDiv$NumberNumber.invoke(NumberNumberDiv.java:323)\n\tat org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite.call(PojoMetaMethodSite.java:56)\n\tat org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)\n\tat org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113)\n\tat org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125)\n\tat Script4.run(Script4.groovy:1)\n\tat org.apache.tinkerpop.gremlin.groovy.jsr223.GremlinGroovyScriptEngine.eval(GremlinGroovyScriptEngine.java:834)\n\tat org.apache.tinkerpop.gremlin.groovy.jsr223.GremlinGroovyScriptEngine.eval(GremlinGroovyScriptEngine.java:547)\n\tat javax.script.AbstractScriptEngine.eval(AbstractScriptEngine.java:233)\n\tat org.apache.tinkerpop.gremlin.groovy.engine.ScriptEngines.eval(ScriptEngines.java:120)\n\tat org.apache.tinkerpop.gremlin.groovy.engine.GremlinExecutor.lambda$eval$2(GremlinExecutor.java:314)\n\tat java.util.concurrent.FutureTask.run(FutureTask.java:266)\n\tat java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)\n\tat java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)\n\tat java.lang.Thread.run(Thread.java:745)\n"
    }

Note that the `Exception-Class` which was added in a previous version has been deprecated and replaced by these new fields.

See: TINKERPOP-1044

#### Gremlin Console Scripting

The `gremlin.sh` command has two flags, `-i` and `-e`, which are used to pass a script and arguments into the Gremlin Console for execution. Those flags now allow for passing multiple scripts and related arguments to be supplied which can yield greater flexibility in automation tasks.

    $ bin/gremlin.sh -i y.groovy 1 2 3 -i x.groovy
    $ bin/gremlin.sh -e y.groovy 1 2 3 -e x.groovy

See: TINKERPOP-1653

#### Path support for by()-, from()-, to()-modulation

It is now possible to extract analyze sub-paths using `from()` and `to()` modulations with respective, path-based steps. Likewise, `simplePath()` and `cyclicPath()` now support, along with `from()` and `to()`, `by()`-modulation so the cyclicity is determined by projections of the path data. This extension is fully backwards compatible.

See: TINKERPOP-1387

#### GraphManager versus DefaultGraphManager

Gremlin Server previously implemented its own final `GraphManager` class. Now, the `GraphManager` has been changed to an interface, and users can supply their own `GraphManager` implementations in their YAML. The previous `GraphManager` class was meant be used by classes internal to Gremlin Server, but it was public so if it was used for some reason by users then then a compile error can be expected. To correct this problem, which will likely manifest as a compile error when trying to create a `new GraphManager()` instance, simply change the code to `new DefaultGraphManager(Settings)`.

In addition to the change mentioned above, several methods on `GraphManager` were deprecated:

- `getGraphs()` should be replaced by the combination of `getGraphNames()` and then `getGraph(String)`

- `getTraversalSources()` is similarly replaced and should instead use a combination of `getTraversalSourceNames()` and `getTraversalSource(String)`

See: TINKERPOP-1438

#### Gremlin-Python Driver

Gremlin-Python now offers a more complete driver implementation that uses connection pooling and the Python `concurrent.futures` module to provide asynchronous I/0 using threading. The default underlying WebSocket client implementation is still provided by Tornado, but it is trivial to plug in another client by defining the `Transport` interface.

Using the `DriverRemoteConnection` class is the exact same as in previous versions; however, `DriverRemoteConnection` now uses the new `Client` class to submit messages to the server.

The `Client` class implementation/interface is based on the Java Driver, with some restrictions. Most notably, Gremlin-Python does not yet implement the `Cluster` class. Instead, `Client` is instantiated directly. Usage is as follows:

    from gremlin_python.driver import client

    client = client.Client('ws://localhost:8182/gremlin', 'g')
    result_set = client.submit('1 + 1')
    future_results = result_set.all()  # returns a concurrent.futures.Future
    results = future_results.result()  # returns a list
    assert results == [2]
    client.close()  # don't forget to close underlying connections

See: TINKERPOP-1599

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### Graph Database Providers

##### SimplePathStep and CyclicPathStep now PathFilterStep

The Gremlin traversal machine use to support two step instructions: `SimplePathStep` and `CyclicPathStep`. These have been replaced by a high-level instruction called `PathFilterStep` which is boolean configured for simple or cyclic paths. Furthermore, `PathFilterStep` also support `from()`-, `to()`-, and `by()`-modulation.

##### LazyBarrierStrategy No Longer End Appends Barriers

`LazyBarrierStrategy` was trying to do to much by considering `Traverser` effects on network I/O by appending an `NoOpBarrierStrategy` to the end of the root traversal. This should not be accomplished by `LazyBarrierStrategy`, but instead by `RemoteStrategy`. `RemoteStrategy` now tries to barrier-append. This may effect the reasoning logic in some `ProviderStrategies`. Most likely not, but just be aware.

See: TINKERPOP-1627

## TinkerPop 3.2.4

Release Date: February 8, 2017

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### TinkerGraph Deserialization

A TinkerGraph deserialized from Gryo or GraphSON is now configured with multi-properties enabled. This change allows TinkerGraphs returned from Gremlin Server to properly return multi-properties, which was a problem seen when subgraphing a graph that contained properties with a setting other than `Cardinality.single`.

This change could be considered breaking in the odd chance that a TinkerGraph returned from Gremlin Server was later mutated, because calls to `property(k,v)` would default to `Cardinality.list` instead of `Cardinality.single`. In the event that this is a problem, simple change calls to `property(k,v)` to `property(Cardinality.single,k,v)` and explicitly set the `Cardinality`.

See: TINKERPOP-1587

#### Traversal Promises

The `Traversal` API now has a new `promise()` method. These methods return a promise in the form of a `CompleteableFuture`. Usage is as follows:

    gremlin> promise = g.V().out().promise{it.next()}
    ==>java.util.concurrent.CompletableFuture@4aa3d36[Completed normally]
    gremlin> promise.join()
    ==>v[3]
    gremlin> promise.isDone()
    ==>true
    gremlin> g.V().out().promise{it.toList()}.thenApply{it.size()}.get()
    ==>6

At this time, this method is only used for traversals that are configured using `withRemote()`.

See: TINKERPOP-1490

#### If/Then-Semantics with Choose Step

Gremlin’s `choose()`-step supports if/then/else-semantics. Thus, to effect if/then-semantics, `identity()` was required. Thus, the following two traversals below are equivalent with the later being possible in this release.

    g.V().choose(hasLabel('person'),out('created'),identity())
    g.V().choose(hasLabel('person'),out('created'))

See: TINKERPOP-1508

#### FastNoSuchElementException converted to regular NoSuchElementException

Previously, a call to `Traversal.next()` that did not have a result would throw a `FastNoSuchElementException`. This has been changed to a regular `NoSuchElementException` that includes the stack trace. Code that explicitly catches `FastNoSuchElementException` should be converted to check for the more general class of `NoSuchElementException`.

See: TINKERPOP-1330

#### ScriptEngine support in gremlin-core

`ScriptEngine` and `GremlinPlugin` infrastructure has been moved from gremlin-groovy to gremlin-core to allow for better re-use across different Gremlin Language Variants. At this point, this change is non-breaking as it was implemented through deprecation.

The basic concept of a `ScriptEngine` has been replaced by the notion of a `GremlinScriptEngine` (i.e. a "ScriptEngine" that is specifically tuned for executing Gremlin-related scripts). "ScriptEngine" infrastructure has been developed to help support this new interface, specifically `GremlinScriptEngineFactory` and `GremlinScriptEngineManager`. Prefer use of this infrastructure when instantiating a `GremlinScriptEngine` rather than trying to instantiate directly.

For example, rather than instantiate a `GremlinGroovyScriptEngine` with the constructor:

    GremlinScriptEngine engine = new GremlinGroovyScriptEngine();

prefer to instantiate it as follows:

    GremlinScriptEngineManager manager = new CachedGremlinScriptEngineManager();
    GremlinScriptEngine engine = manager.getEngineByName("gremlin-groovy");

Related to the addition of `GremlinScriptEngine`, `org.apache.tinkerpop.gremlin.groovy.plugin.GremlinPlugin` in gremlin-groovy has been deprecated and then replaced by `org.apache.tinkerpop.gremlin.jsr223.GremlinPlugin`. The new version of `GremlinPlugin` is similar but does carry some new methods to implement that involves the new `Customizer` interface. The `Customizer` interface is the way in which `GremlinScriptEngine` instance can be configured with imports, initialization scripts, compiler options, etc.

Note that a `GremlinPlugin` can be applied to a `GremlinScriptEngine` by adding it to the `GremlinScriptEngineManager` that creates it.

    GremlinScriptEngineManager manager = new CachedGremlinScriptEngineManager();
    manager.addPlugin(ImportGremlinPlugin.build().classImports(java.awt.Color.class).create());
    GremlinScriptEngine engine = manager.getEngineByName("gremlin-groovy");

All of this new infrastructure is currently optional on the 3.2.x line of code. More detailed documentation will for these changes will be supplied as part of 3.3.0 when these features become mandatory and the deprecated code is removed.

See: TINKERPOP-1562

#### SSL Client Authentication

Added new server configuration option `ssl.needClientAuth`.

See: TINKERPOP-1602

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### Graph Database Providers

##### CloseableIterator

Prior to TinkerPop 3.x, Blueprints had the notion of a `CloseableIterable` which exposed a way for Graph Providers to offer a way to release resources that might have been opened when returning vertices and edges. That interface was never exposed in TinkerPop 3.x, but has now been made available via the new `CloseableIterator`. Providers may choose to use this interface or not when returning values from `Graph.vertices()` and `Graph.edges()`.

It will be up to users to know whether or not they need to call `close()`. Of course, users should typically not be operating with the Graph Structure API, so it’s unlikely that they would be calling these methods directly in the first place. It is more likely that users will be calling `Traversal.close()`. This method will essentially iterate the steps of the `Traversal` and simply call `close()` on any steps that implement `AutoCloseable`. By default, `GraphStep` now implements `AutoCloseable` which most Graph Providers will extend upon (as was done with TinkerGraph’s `TinkerGraphStep`), so the integration should largely come for free if the provider simply returns a `CloseableIterator` from `Graph.vertices()` and `Graph.edges()`.

See: TINKERPOP-1589

##### HasContainer AndP Splitting

Previously, `GraphTraversal` made it easy for providers to analyze `P`-predicates in `HasContainers`, but always splitting `AndP` predicates into their component parts. This helper behavior is no longer provided because, 1.) `AndP` can be inserted into a `XXXStep` in other ways, 2.) the providers `XXXStep` should process `AndP` regardless of `GraphTraversal` helper, and 3.) the `GraphTraversal` helper did not recursively split. A simple way to split `AndP` in any custom `XXXStep` that implements `HasContainerHolder` is to use the following method:

    @Override
    public void addHasContainer(final HasContainer hasContainer) {
      if (hasContainer.getPredicate() instanceof AndP) {
        for (final P<?> predicate : ((AndP<?>) hasContainer.getPredicate()).getPredicates()) {
          this.addHasContainer(new HasContainer(hasContainer.getKey(), predicate));
        }
      } else
        this.hasContainers.add(hasContainer);
    }

See: TINKERPOP-1482, TINKERPOP-1502

##### Duplicate Multi-Properties

Added `supportsDuplicateMultiProperties` to `VertexFeatures` so that graph provider who only support unique values as multi-properties have more flexibility in describing their graph capabilities.

See: TINKERPOP-919

##### Deprecated OptIn

In 3.2.1, all `junit-benchmark` performance tests were deprecated. At that time, the `OptIn` representations of these tests should have been deprecated as well, but they were not. That omission has been remedied now. Specifically, the following fields were deprecated:

- `OptIn.SUITE_GROOVY_ENVIRONMENT_PERFORMANCE`

- `OptIn.SUITE_PROCESS_PERFORMANCE`

- `OptIn.SUITE_STRUCTURE_PERFORMANCE`

As of 3.2.4, the following test suites were also deprecated:

- `OptIn.SUITE_GROOVY_PROCESS_STANDARD`

- `OptIn.SUITE_GROOVY_PROCESS_COMPUTER`

- `OptIn.SUITE_GROOVY_ENVIRONMENT`

- `OptIn.SUITE_GROOVY_ENVIRONMENT_INTEGRATE`

Future testing of `gremlin-groovy` (and language variants in general) will be handled differently and will not require a Graph Provider to validate its operations with it. Graph Providers may now choose to remove these tests from their test suites, which should reduce the testing burden.

See: TINKERPOP-1610

##### Deprecated getInstance()

TinkerPop has generally preferred static `instance()` methods over `getInstance()`, but `getInstance()` was used in some cases nonetheless. As of this release, `getInstance()` methods have been deprecated in favor of `instance()`. Of specific note, custom `IoRegistry` (as related to IO in general) and `Supplier<ClassResolver>` (as related to Gryo serialization in general) now both prefer `instance()` over `getInstance()` given this deprecation.

See: TINKERPOP-1530

#### Drivers Providers

##### Force Close

Closing a session will first attempt a proper close of any open transactions. A problem can occur, however, if there is a long run job (e.g. an OLAP-based traversal) executing, as that job will block the calls to close the transactions. By exercising the option to a do a "forced close" the session will skip trying to close the transactions and just attempt to interrupt the long run job. By not closing transactions, the session leaves it up to the underlying graph database to sort out how it will deal with those orphaned transactions. On the positive side though (for those graphs which do that well) , long run jobs have the opportunity to be cancelled without waiting for a timeout of the job itself which will allow resources to be released earlier.

The "force" argument is passed on the "close" message and is a boolean value. This is an optional argument to "close" and defaults to `false`.

See: TINKERPOP-932, Provider Documentation - Session OpProcessor

##### SASL Authentication

Gremlin Supports SASL based authentication. The server accepts either a byte array or Base64 encoded String as the in the `sasl` argument on the `RequestMessage`, however it sends back a byte array only. Some serializers or serializer configurations don’t work well with that approach (specifically the "toString" configuration on the Gryo serializer) as the byte array is returned in the `ResponseMessage` result. In the case of the "toString" serializer the byte array gets "toString’d" and the can’t be read by the client.

In 3.2.4, the byte array is still returned in the `ResponseMessage` result, but is also returned in the status attributes under a `sasl` key as a Base64 encoded string. In this way, the client has options on how it chooses to process the authentication response and the change remains backward compatible. Drivers should upgrade to using the Base64 encoded string however as the old approach will likely be removed in the future.

See: TINKERPOP-1600

## TinkerPop 3.2.3

Release Date: October 17, 2016

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Renamed Null Result Preference

In 3.2.2, the Gremlin Console introduced a setting called `empty.result.indicator`, which controlled the output that was presented when no result was returned. For consistency, this setting has been renamed to `result.indicator.null` and can be set as follows:

    gremlin> graph = TinkerGraph.open()
    ==>tinkergraph[vertices:0 edges:0]
    gremlin> graph.close()
    ==>null
    gremlin> :set result.indicator.null nil
    gremlin> graph = TinkerGraph.open()
    ==>tinkergraph[vertices:0 edges:0]
    gremlin> graph.close()
    ==>nil
    gremlin> :set result.indicator.null ""
    gremlin> graph = TinkerGraph.open()
    ==>tinkergraph[vertices:0 edges:0]
    gremlin> graph.close()
    gremlin>

See: TINKERPOP-1409

#### Java Driver Keep-Alive

The Java Driver now has a `keepAliveInterval` setting, which controls the amount of time in milliseconds it should wait on an inactive connection before it sends a message to the server to keep the connection maintained. This should help environments that use a load balancer in front of Gremlin Server by ensuring connections are actively maintained even during periods of inactivity.

See: TINKERPOP-1249

#### Where Step Supports By-Modulation

It is now possible to use `by()` with `where()` predicate-based steps. Previously, without using `match()`, if you wanted to know who was older than their friend, the following traversal would be used.

    gremlin> g.V().as('a').out('knows').as('b').
    ......1>   filter(select('a','b').by('age').where('a', lt('b')))
    ==>v[4]

Now, with `where().by()` support, the above traversal can be expressed more succinctly and more naturally as follows.

    gremlin> g.V().as('a').out('knows').as('b').
    ......1>   where('a', lt('b')).by('age')
    ==>v[4]

See: TINKERPOP-1330

#### Change In has() Method Signatures

The TinkerPop 3.2.2 release unintentionally introduced a breaking change for some `has()` method overloads. In particular the behavior for single item array arguments was changed:

    gremlin> g.V().hasLabel(["software"] as String[]).count()
    ==>0

Prior this change single item arrays were treated like there was only that single item:

    gremlin> g.V().hasLabel(["software"] as String[]).count()
    ==>2
    gremlin> g.V().hasLabel("software").count()
    ==>2

TinkerPop 3.2.3 fixes this misbehavior and all `has()` method overloads behave like before, except that they no longer support no arguments.

#### Deprecated reconnectInitialDelay

The `reconnectInitialDelay` setting on the `Cluster` builder has been deprecated. It no longer serves any purpose. The value for the "initial delay" now comes from `reconnectInterval` (there are no longer two separate settings to control).

See: TINKERPOP-1460

#### TraversalSource.close()

`TraversalSource` now implements `AutoCloseable`, which means that the `close()` method is now available. This new method is important in cases where `withRemote()` is used, as `withRemote()` can open "expensive" resources that need to be released.

In the case of TinkerPop’s `DriverRemoteConnection`, `close()` will destroy the `Client` instance that is created internally by `withRemote()` as shown below:

    gremlin> graph = EmptyGraph.instance()
    ==>emptygraph[empty]
    gremlin> g = graph.traversal().withRemote('conf/remote-graph.properties')
    ==>graphtraversalsource[emptygraph[empty], standard]
    gremlin> g.close()
    gremlin>

Note that the `withRemote()` method will call `close()` on a `RemoteConnection` passed directly to it as well, so there is no need to do that manually.

See: TINKERPOP-790

#### IO Reference Documentation

There is new reference documentation for the various IO formats. The documentation provides more details and samples that should be helpful to users and providers who intend to work directly with the TinkerPop supported serialization formats: GraphML, GraphSON and Gryo.

See: IO Reference Documentation

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### Graph System Providers

##### Default LazyBarrierStrategy

`LazyBarrierStrategy` has been included as a default strategy. `LazyBarrierStrategy` walks a traversal and looks for "flatMaps" (`out()`, `in()`, `both()`, `values()`, `V()`, etc.) and adds "lazy barriers" to dam up the stream so to increase the probability of bulking the traversers. One of the side-effects is that:

    g.V().out().V().has(a)

is compiled to:

    g.V().out().barrier().V().barrier().has(a)

Given that `LazyBarrierStrategy` is an `OptimizationStrategy`, it comes before `ProviderOptimizationStrategies`. Thus, if the provider’s `XXXGraphStepStrategy` simply walks from the second `V()` looking for `has()`-only, it will not be able to pull in the `has()` cause the `barrier()` blocks it. Please see the updates to `TinkerGraphStepStrategy` and how it acknowledges `NoOpBarrierSteps` (i.e. `barrier()`) skipping over them and “left”-propagating labels to the previous step.

See: TINKERPOP-1488

##### Configurable Strategies

If the provider has non-configurable `TraversalStrategy` classes, those classes should expose a static `instance()`-method. This is typical and thus, backwards compatible. However, if the provider has a `TraversalStrategy` that can be configured (e.g. via a `Builder`), then it should expose a static `create(Configuration)`-method, where the keys of the configuration are the method names of the `Builder` and the values are the method arguments. For instance, for Gremlin-Python to create a `SubgraphStrategy`, it does the following:

    g = Graph().traversal().withRemote(connection).
            withStrategies(SubgraphStrategy(vertices=__.hasLabel('person'),edges=__.has('weight',gt(0.5))))

The `SubgraphStrategy.create(Configuration)`-method is defined as:

    public static SubgraphStrategy create(final Configuration configuration) {
        final Builder builder = SubgraphStrategy.build();
        if (configuration.containsKey(VERTICES))
            builder.vertices((Traversal) configuration.getProperty(VERTICES));
        if (configuration.containsKey(EDGES))
            builder.edges((Traversal) configuration.getProperty(EDGES));
        if (configuration.containsKey(VERTEX_PROPERTIES))
            builder.vertexProperties((Traversal) configuration.getProperty(VERTEX_PROPERTIES));
        return builder.create();
    }

Finally, in order to make serialization possible from JVM-based Gremlin language variants, all strategies have a `TraverserStrategy.getConfiguration()` method which returns a `Configuration` that can be used to `create()` the `TraversalStrategy`.

The `SubgraphStrategy.getConfiguration()`-method is defined as:

    @Override
    public Configuration getConfiguration() {
        final Map<String, Object> map = new HashMap<>();
        map.put(STRATEGY, SubgraphStrategy.class.getCanonicalName());
        if (null != this.vertexCriterion)
            map.put(VERTICES, this.vertexCriterion);
        if (null != this.edgeCriterion)
                map.put(EDGES, this.edgeCriterion);
        if (null != this.vertexPropertyCriterion)
            map.put(VERTEX_PROPERTIES, this.vertexPropertyCriterion);
        return new MapConfiguration(map);
    }

The default implementation of `TraversalStrategy.getConfiguration()` is defined as:

    public default Configuration getConfiguration() {
        return new BaseConfiguration();
    }

Thus, if the provider does not have any "builder"-based strategies, then no updates to their strategies are required.

See: TINKERPOP-1455

##### Deprecated elementNotFound

Both `Graph.Exceptions.elementNotFound()` methods have been deprecated. These exceptions were being asserted in the test suite but were not being used anywhere in `gremlin-core` itself. The assertions have been modified to simply assert that `NoSuchElementException` was thrown, which is precisely the behavior that was being indirectly asserted when `Graph.Exceptions.elementNotFound()` were being used.

Providers should not need to take any action in this case for their tests to pass, however, it would be wise to remove uses of these exception builders as they will be removed in the future.

See: TINKERPOP-944

##### Hidden Step Labels for Compilation Only

In order for `SubgraphStrategy` to work, it was necessary to have multi-level children communicate with one another via hidden step labels. It was decided that hidden step labels are for compilation purposes only and will be removed prior to traversal evaluation. This is a valid decision given that hidden labels for graph system providers are not allowed to be used by users. Likewise, hidden labels for steps should not be allowed be used by users as well.

##### PropertyMapStep with Selection Traversal

`PropertyMapStep` now supports selection of properties via child property traversal. If a provider was relying solely on the provided property keys in a `ProviderOptimizationStrategy`, they will need to check if there is a child traversal and if so, use that in their introspection for respective strategies. This model was created to support `SubgraphStrategy.vertexProperties()` filtering.

See: TINKERPOP-1456, TINKERPOP-844

##### ConnectiveP Nesting Inlined

There was a bug in `ConnectiveP` (`AndP`/`OrP`), where `eq(1).and(eq(2).and(eq(3)))` was `AndP(eq(1),AndP(eq(2),eq(3)))` instead of unnested/inlined as `AndP(eq(1),eq(2),eq(3))`. Likewise, for `OrP`. If a provider was leveraging `ConnectiveP` predicates for their custom steps (e.g. graph- or vertex-centric index lookups), then they should be aware of the inlining and can simplify any and/or-tree walking code in their respective `ProviderOptimizationStrategy`.

See: TINKERPOP-1470

## TinkerPop 3.2.2

Release Date: September 6, 2016

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### GraphSON 2.0

GraphSON 2.0 has been introduced to improve and normalize the format of types embedded in GraphSON.

See: TINKERPOP-1274, Reference Documentation - GraphSON 2.0.

#### Log4j Dependencies

There were a number of changes to the Log4j dependencies in the various modules. Log4j was formerly included as part of the `slf4j-log4j12` in `gremlin-core`, however that "forced" use of Log4j as a logger implementation when that really wasn’t necessary or desired. If a project depended on `gremlin-core` or other TinkerPop project to get its Log4j implementation then those applications will need to now include the dependency themselves directly.

Note that Gremlin Server and Gremlin Console explicitly package Log4j in their respective binary distributions.

See: TINKERPOP-1151

#### Default for gremlinPool

The `gremlinPool` setting in Gremlin Server is now defaulted to zero. When set to zero, Gremlin Server will use the value provided by `Runtime.availableProcessors()` to set the pool size. Note that the packaged YAML files no longer contain the thread pool settings as all are now driven by sensible defaults. Obviously these values can be added and overridden as needed.

See: TINKERPOP-1373

#### New Console Features

The Gremlin Console can now have its text colorized. For example, you can set the color of the Gremlin ascii art to the more natural color of green by using the `:set` command:

    gremlin> :set gremlin.color green

It is also possible to colorize results, like vertices, edges, and other common returns. Please see the reference documentation for more details on all the settings.

The console also now includes better multi-line support:

    gremlin> g.V().out().
    ......1>       has('name','josh').
    ......2>       out('created')
    ==>v[5]
    ==>v[3]

This is a nice feature in that it can help you understand if a line is incomplete and unevaluated.

See: TINKERPOP-1285, TINKERPOP-1037, Reference Documentation - Console Preferences

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### Graph System Providers

##### Deprecated Io.Builder.registry()

The `Io.Builder.registry()` has been deprecated in favor of `Io.Builder.onMapper(Consumer<Mapper>)`. This change gives the `Graph` implementation greater flexibility over how to modify the `Mapper` implementation. In most cases, the implementation will simply add its `IoRegistry` to allow the `Mapper` access to custom serialization classes, but this approach makes it possible to also set other specific settings that aren’t generalized across all IO implementations. A good example of this type of usage would be to provide a custom `ClassRessolver` implementation to a `GryoMapper`.

See: TINKERPOP-1402

##### Log4j Dependencies

There were a number of changes to the Log4j dependencies in the various modules. Log4j was formerly included as part of the `slf4j-log4j12` in `gremlin-core`, however that "forced" use of log4j as a logger implementation when that really wasn’t necessary or desired. The `slf4j-log4j12` dependency is now in "test" scope for most of the modules. The exception to that rule is `gremlin-test` which prescribes it as "optional". That change means that developers dependending on `gremlin-test` (or `gremlin-groovy-test`) will need to explicitly specify it as a dependency in their `pom.xml` (or a different slf4j implementation if that better suits them).

See: TINKERPOP-1151

#### Drivers Providers

##### GraphSON 2.0

Drivers providers can exploit the new format of typed values JSON serialization offered by GraphSON 2.0. This format has been created to allow easy and agnostic parsing of a GraphSON payload without type loss. Drivers of non-Java languages can then implement their own mapping of the GraphSON’s language agnostic type IDs (e.g. `UUID`, `LocalDate`) to the appropriate representation for the driver’s language.

See: TINKERPOP-1274, Reference Documentation - GraphSON 2.0.

##### Traversal Serialization

There was an "internal" serialization format in place for `Traversal` which allowed one to be submitted to Gremlin Server directly over `RemoteGraph`. That format has been removed completely and is wholly replaced by the non-JVM specific approach of serializing `Bytecode`.

See: TINKERPOP-1392

## TinkerPop 3.2.1

Release Date: July 18, 2016

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Gephi Plugin

The Gephi Plugin has been updated to support Gephi 0.9.x. Please upgrade to this latest version to use the Gephi Plugin for Gremlin Console.

See: TINKERPOP-1297

#### GryoMapper Construction

It is now possible to override existing serializers with calls to `addCustom` on the `GryoMapper` builder. This option allows complete control over the serializers used by Gryo. Of course, this also makes it possible to produce completely non-compliant Gryo files. This feature should be used with caution.

#### TraversalVertexProgram

`TraversalVertexProgram` always maintained a `HALTED_TRAVERSERS` `TraverserSet` for each vertex throughout the life of the OLAP computation. However, if there are no halted traversers in the set, then there is no point in keeping that compute property around as without it, time and space can be saved. Users that have `VertexPrograms` that are chained off of `TraversalVertexProgram` and have previously assumed that `HALTED_TRAVERSERS` always exists at each vertex, should no longer assume that.

    TraverserSet haltedTraversers = vertex.value(TraversalVertexProgram.HALTED_TRAVERSERS);
    // good code
    TraverserSet haltedTraversers = vertex.property(TraversalVertexProgram.HALTED_TRAVERSERS).orElse(new TraverserSet());

#### Interrupting Traversals

Traversals now better respect calls to `Thread.interrupt()`, which mean that a running `Traversal` can now be cancelled. There are some limitations that remain, but most OLTP-based traversals should cancel without issue. OLAP-based traversals for Spark will also cancel and clean up running jobs in Spark itself. Mileage may vary on other process implementations and it is possible that graph providers could potentially write custom step implementations that prevent interruption. If it is found that there are configurations or specific traversals that do not respect interruption, please mention them on the mailing list.

See: TINKERPOP-946

#### Gremlin Console Flags

Gremlin Console had several methods for executing scripts from file at the start-up of `bin/gremlin.sh`. There were two options:

    bin/gremlin.sh script.groovy    //1
    bin/gremlin.sh -e script.groovy //2

1. The `script.groovy` would be executed as a console initialization script setting the console up for use and leaving it open when the script completed successfully or closing it if the script failed.

2. The `script.groovy` would be executed by the `ScriptExecutor` which meant that commands for the Gremlin Console, such as `:remote` and `:>` would not be respected.

Changes in this version of TinkerPop have added much more flexibility here and only a minor breaking change should be considered when using this version. First of all, recognize that hese two lines are currently equivalent:

    bin/gremlin.sh script.groovy
    bin/gremlin.sh -i script.groovy

but users should start to explicitly specify the `-i` flag as TinkerPop will eventually remove the old syntax. Despite the one used beware of the fact that neither will close the console on script failure anymore. In that sense, this behavior represents a breaking change to consider. To ensure the console closes on failure or success, a script will have to use the `-e` option.

The console also has a number of new features in addition to `-e` and `-i`:

- View the available flags for the console with `-h`.

- Control console output with `-D`, `-Q` and -`V`

- Get line numbers on script failures passed to `-i` and `-e`.

See: TINKERPOP-1268, TINKERPOP-1155, TINKERPOP-1156, TINKERPOP-1157, Reference Documentation - Interactive Mode, Reference Documentation - Execution Mode

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### Graph System Providers

##### VertexComputing API Change

The `VertexComputing` API is used by steps that wrap a `VertexProgram`. There is a method called `VertexComputing.generateProgram()` that has changed which now takes a second argument of `Memory`. To upgrade, simply fix the method signature of your `VertexComputing` implementations. The `Memory` argument can be safely ignored to effect the exact same semantics as prior. However, now previous OLAP job `Memory` can be leveraged when constructing the next `VertexProgram` in an OLAP traversal chain.

##### Interrupting Traversals

Several tests have been added to the TinkerPop test suite to validate that a `Traversal` can be cancelled with `Thread.interrupt()`. The test suite does not cover all possible traversal scenarios. When implementing custom steps, providers should take care to not ignore an `InterruptionException` that might be thrown in their code and to be sure to check `Thread.isInterrupted()` as needed to ensure that the step remains cancellation compliant.

See: TINKERPOP-946

##### Performance Tests

All "performance" tests have been deprecated. In the previous 3.2.0-incubating release, the `ProcessPerformanceSuite` and `TraversalPerformanceTest` were deprecated, but some other tests remained. It is the remaining tests that have been deprecated on this release:

- `StructurePerformanceSuite

  - `GraphReadPerformanceTest`

  - `GraphWriterPerformanceTest`

- `GroovyEnvironmentPerformanceSuite`

  - `SugarLoaderPerformanceTest`

  - `GremlinExecutorPerformanceTest`

- Gremlin Server related performance tests

- TinkerGraph related performance tests

Providers should implement their own performance tests and not rely on these deprecated tests as they will be removed in a future release along with the "JUnit Benchmarks" dependency.

See: TINKERPOP-1294

#### Graph Database Providers

##### Transaction Tests

Tests and assertions were added to the structure test suite to validate that transaction status was in the appropriate state following calls to close the transaction with `commit()` or `rollback()`. It is unlikely that this change would cause test breaks for providers, unless the transaction status was inherently disconnected from calls to close the transaction somehow.

In addition, other tests were added to enforce the expected semantics for threaded transactions. Threaded transactions are expected to behave like manual transactions. They should be open automatically when they are created and once closed should no longer be used. This behavior is not new and is the typical expected method for working with these types of transactions. The test suite just requires that the provider implementation conform to these semantics.

See: TINKERPOP-947, TINKERPOP-1059

##### GraphFilter and GraphFilterStrategy

`GraphFilter` has been significantly advanced where the determination of an edge direction/label legality is more stringent. Along with this, `GraphFilter.getLegallyPositiveEdgeLabels()` has been added as a helper method to make it easier for `GraphComputer` providers to know the space of labels being accessed by the traversal and thus, better enable provider-specific push-down predicates.

Note that `GraphFilterStrategy` is now a default `TraversalStrategy` registered with `GraphComputer.` If `GraphFilter` is expensive for the underlying `GraphComputer` implementation, it can be deactivated as is done for `TinkerGraphComputer`.

    static {
      TraversalStrategies.GlobalCache.registerStrategies(TinkerGraphComputer.class,
        TraversalStrategies.GlobalCache.getStrategies(GraphComputer.class).clone().removeStrategies(GraphFilterStrategy.class));
    }

See: TINKERPOP-1293

#### Graph Language Providers

##### VertexTest Signatures

The method signatures of `get_g_VXlistXv1_v2_v3XX_name` and `get_g_VXlistX1_2_3XX_name` of `VertexTest` were changed to take arguments for the `Traversal` to be constructed by extending classes.

## TinkerPop 3.2.0

Release Date: Release Date: April 8, 2016

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Hadoop FileSystem Variable

The `HadoopGremlinPlugin` defines two variables: `hdfs` and `fs`. The first is a reference to the HDFS `FileSystemStorage` and the latter is a reference to the local `FileSystemStorage`. Prior to 3.2.x, `fs` was called `local`. However, there was a variable name conflict with `Scope.local`. As such `local` is now `fs`. This issue existed prior to 3.2.x, but was not realized until this release. Finally, this only effects Gremlin Console users.

#### Hadoop Configurations

Note that `gremlin.hadoop.graphInputFormat`, `gremlin.hadoop.graphOutputFormat`, `gremlin.spark.graphInputRDD`, and `gremlin.spark.graphOuputRDD` have all been deprecated. Using them still works, but moving forward, users only need to leverage `gremlin.hadoop.graphReader` and `gremlin.hadoop.graphWriter`. An example properties file snippet is provided below.

    gremlin.graph=org.apache.tinkerpop.gremlin.hadoop.structure.HadoopGraph
    gremlin.hadoop.graphReader=org.apache.tinkerpop.gremlin.hadoop.structure.io.gryo.GryoInputFormat
    gremlin.hadoop.graphWriter=org.apache.tinkerpop.gremlin.hadoop.structure.io.gryo.GryoOutputFormat
    gremlin.hadoop.jarsInDistributedCache=true
    gremlin.hadoop.defaultGraphComputer=org.apache.tinkerpop.gremlin.spark.process.computer.SparkGraphComputer

See: TINKERPOP-1082, TINKERPOP-1222

#### TraversalSideEffects Update

There were changes to `TraversalSideEffect` both at the semantic level and at the API level. Users that have traversals of the form `sideEffect{…​}` that leverage global side-effects should read the following carefully. If the user’s traversals do not use lambda-based side-effect steps (e.g. `groupCount("m")`), then the changes below will not effect them. Moreover, if user’s traversal only uses `sideEffect{…​}` with closure (non-`TraversalSideEffect`) data references, then the changes below will not effect them. If the user’s traversal uses sideEffects in OLTP only, the changes below will not effect them. Finally, providers should not be effected by the changes save any tests cases.

##### TraversalSideEffects Get API Change

`TraversalSideEffects` can now logically operate within a distributed OLAP environment. In order to make this possible, it is necessary that each side-effect be registered with a reducing `BinaryOperator`. This binary operator will combine distributed updates into a single global side-effect at the master traversal. Many of the methods in `TraversalSideEffect` have been `Deprecated`, but they are backwards compatible save that `TraversalSideEffects.get()` no longer returns an `Optional`, but instead throws an `IllegalArgumentException`. While the `Optional` semantics could have remained, it was deemed best to directly return the side-effect value to reduce object creation costs and because all side-effects must be registered apriori, there is never a reason why an unknown side-effect key would be used. In short:

    // change
    traversal.getSideEffects().get("m").get()
    // to
    traversal.getSideEffects().get("m")

##### TraversalSideEffects Registration Requirement

All `TraversalSideEffects` must be registered upfront. This is because, in OLAP, side-effects map to `Memory` compute keys and as such, must be declared prior to the execution of the `TraversalVertexProgram`. If a user’s traversal creates a side-effect mid-traversal, it will fail. The traversal must use `GraphTraversalSource.withSideEffect()` to declare the side-effects it will use during its execution lifetime. If the user’s traversals use standard side-effect Gremlin steps (e.g. `group("m")`), then no changes are required.

See: TINKERPOP-1192

##### TraversalSideEffects Add Requirement

In a distributed environment, a side-effect can not be mutated and be expected to exist in the mutated form at the final, aggregated, master traversal. For instance, if the side-effect "myCount" references a `Long`, the `Long` can not be updated directly via `sideEffects.set("myCount", sideEffects.get("myCount") + 1)`. Instead, it must rely on the registered reducer to do the merging and thus, the `Step` must do `sideEffect.add("mySet",1)`, where the registered reducer is `Operator.sum`. Thus, the below will increment "a". If no operator was provided, then the operator is assumed `Operator.assign` and the final result of "a" would be 1. Note that `Traverser.sideEffects(key,value)` uses `TraversalSideEffect.add()`.

    gremlin> traversal = g.withSideEffect('a',0,sum).V().out().sideEffect{it.sideEffects('a',1)}
    ==>v[3]
    ==>v[2]
    ==>v[4]
    ==>v[5]
    ==>v[3]
    ==>v[3]
    gremlin> traversal.getSideEffects().get('a')
    ==>6
    gremlin> traversal = g.withSideEffect('a',0).V().out().sideEffect{it.sideEffects('a',1)}
    ==>v[3]
    ==>v[2]
    ==>v[4]
    ==>v[5]
    ==>v[3]
    ==>v[3]
    gremlin> traversal.getSideEffects().get('a')
    ==>1

See: TINKERPOP-1192, TINKERPOP-1166

#### ProfileStep Update and GraphTraversal API Change

The `profile()`-step has been refactored into 2 steps —`ProfileStep` and `ProfileSideEffectStep`. Users who previously used the `profile()` in conjunction with `cap(TraversalMetrics.METRICS_KEY)` can now simply omit the cap step. Users who retrieved `TraversalMetrics` from the side-effects after iteration can still do so, but will need to specify a side-effect key when using the `profile()`. For example, `profile("myMetrics")`.

See: TINKERPOP-958

#### BranchStep Bug Fix

There was a bug in `BranchStep` that also rears itself in subclass steps such as `UnionStep` and `ChooseStep`. For traversals with branches that have barriers (e.g. `count()`, `max()`, `groupCount()`, etc.), the traversal needs to be updated. For instance, if a traversal is of the form `g.V().union(out().count(),both().count())`, the result is now different (the bug fix yields a different output). In order to yield the same result, the traversal should be rewritten as `g.V().local(union(out().count(),both().count()))`. Note that if a branch does not have a barrier, then no changes are required. For instance, `g.V().union(out(),both())` does not need to be updated. Moreover, if the user’s traversal already used the `local()`-form, then no change are required either.

See: TINKERPOP-1188

#### MemoryComputeKey and VertexComputeKey

Users that have custom `VertexProgram` implementations will need to change their implementations to support the new `VertexComputeKey` and `MemoryComputeKey` classes. In the `VertexPrograms` provided by TinkerPop, these changes were trivial, taking less than 5 minutes to make all the requisite updates.

- `VertexProgram.getVertexComputeKeys()` returns a `Set<VertexComputeKey>`. No longer a `Set<String>`. Use `VertexComputeKey.of(String key,boolean transient)` to generate a `VertexComputeKey`. Transient keys were not supported in the past, so to make the implementation semantically equivalent, the boolean transient should be false.

- `VertexProgram.getMemoryComputeKeys()` returns a `Set<MemoryComputeKey>`. No longer a `Set<String>`. Use `MemoryComputeKey.of(String key, BinaryOperator reducer, boolean broadcast, boolean transient)` to generate a `MemoryComputeKey`. Broadcasting and transients were not supported in the past so to make the implementation semantically equivalent, the boolean broadcast should be true and the boolean transient should be false.

An example migration looks as follows. What might currently look like:

    public Set<String> getMemoryComputeKeys() {
       return new HashSet<>(Arrays.asList("a","b","c"))
    }

Should now look like:

    public Set<MemoryComputeKey> getMemoryComputeKeys() {
      return new HashSet<>(Arrays.asList(
        MemoryComputeKey.of("a", Operator.and, true, false),
        MemoryComputeKey.of("b", Operator.sum, true, false),
        MemoryComputeKey.of("c", Operator.or, true, false)))
    }

A similar patterns should also be used for `VertexProgram.getVertexComputeKeys()`.

See: TINKERPOP-1162

#### SparkGraphComputer and GiraphGraphComputer Persistence

The `MapReduce`-based steps in `TraversalVertexProgram` have been removed and replaced using a new `Memory`-reduction model. `MapReduce` jobs always created a persistence footprint, e.g. in HDFS. `Memory` data was never persisted to HDFS. As such, there will be no data on the disk that is accessible. For instance, there is no more `~reducing`, `~traversers`, and specially named side-effects such as `m` from a `groupCount('m')`. The data is still accessible via `ComputerResult.memory()`, it simply does not have a corresponding on-disk representation.

#### RemoteGraph

`RemoteGraph` is a lightweight `Graph` implementation that acts as a proxy for sending traversals to Gremlin Server for remote execution. It is an interesting alternative to the other methods for connecting to Gremlin Server in that all other methods involved construction of a `String` representation of the `Traversal` which is then submitted as a script to Gremlin Server (via driver or REST).

    gremlin> graph = RemoteGraph.open('conf/remote-graph.properties')
    ==>remotegraph[DriverServerConnection-localhost/127.0.0.1:8182 [graph='graph]]
    gremlin> g = graph.traversal()
    ==>graphtraversalsource[remotegraph[DriverServerConnection-localhost/127.0.0.1:8182 [graph='graph]], standard]
    gremlin> g.V().valueMap(true)
    ==>[name:[marko], label:person, id:1, age:[29]]
    ==>[name:[vadas], label:person, id:2, age:[27]]
    ==>[name:[lop], label:software, id:3, lang:[java]]
    ==>[name:[josh], label:person, id:4, age:[32]]
    ==>[name:[ripple], label:software, id:5, lang:[java]]
    ==>[name:[peter], label:person, id:6, age:[35]]

Note that `g.V().valueMap(true)` is executing in Gremlin Server and not locally in the console.

See: TINKERPOP-575, Reference Documentation - Remote Graph

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### Graph System Providers

##### GraphStep Compilation Requirement

OLTP graph providers that have a custom `GraphStep` implementation should ensure that `g.V().hasId(x)` and `g.V(x)` compile to the same representation. This ensures a consistent user experience around random access of elements based on ids (as opposed to potentially the former doing a linear scan). A static helper method called `GraphStep.processHasContainerIds()` has been added. `TinkerGraphStepStrategy` was updated as such:

    ((HasContainerHolder) currentStep).getHasContainers().forEach(tinkerGraphStep::addHasContainer);

is now

    ((HasContainerHolder) currentStep).getHasContainers().forEach(hasContainer -> {
      if (!GraphStep.processHasContainerIds(tinkerGraphStep, hasContainer))
        tinkerGraphStep.addHasContainer(hasContainer);
    });

See: TINKERPOP-1219

##### Step API Update

The `Step` interface is fundamental to Gremlin. `Step.processNextStart()` and `Step.next()` both returned `Traverser<E>`. We had so many `Traverser.asAdmin()` and direct typecast calls throughout (especially in `TraversalVertexProgram`) that it was deemed prudent to have `Step.processNextStart()` and `Step.next()` return `Traverser.Admin<E>`. Moreover it makes sense as this is internal logic where `Admins` are always needed. Providers with their own step definitions will simply need to change the method signatures of `Step.processNextStart()` and `Step.next()`. No logic update is required — save that `asAdmin()` can be safely removed if used. Also, `Step.addStart()` and `Step.addStarts()` take `Traverser.Admin<S>` and `Iterator<Traverser.Admin<S>>`, respectively.

##### Traversal API Update

The way in which `TraverserRequirements` are calculated has been changed (for the better). The ramification is that post compilation requirement additions no longer make sense and should not be allowed. To enforce this, `Traversal.addTraverserRequirement()` method has been removed from the interface. Moreover, providers/users should never be able to add requirements manually (this should all be inferred from the end compilation). However, if need be, there is always `RequirementStrategy` which will allow the provider to add a requirement at strategy application time (though again, there should not be a reason to do so).

##### ComparatorHolder API Change

Providers that either have their own `ComparatorHolder` implementation or reason on `OrderXXXStep` will need to update their code. `ComparatorHolder` now returns `List<Pair<Traversal,Comparator>>`. This has greatly reduced the complexity of comparison-based steps like `OrderXXXStep`. However, its a breaking API change that is trivial to update to, just some awareness is required.

See: TINKERPOP-1209

##### GraphComputer Semantics and API

Providers that have a custom `GraphComputer` implementation will have a lot to handle. Note that if the graph system simply uses `SparkGraphComputer` or `GiraphGraphComputer` provided by TinkerPop, then no updates are required. This only effects providers that have their own custom `GraphComputer` implementations.

`Memory` updates:

- Any `BinaryOperator` can be used for reduction and is made explicit in the `MemoryComputeKey`.

- `MemoryComputeKeys` can be marked transient and must be removed from the resultant `ComputerResult.memory()`.

- `MemoryComputeKeys` can be specified to not broadcast and thus, must not be available to workers to read in `VertexProgram.execute()`.

- The `Memory` API has been changed. No more `incr()`, `and()`, etc. Now its just `set()` (setup/terminate) and `add()` (execute).

`VertexProgram` updates:

- `VertexComputeKeys` can be marked transient and must be removed from the resultant `ComputerResult.graph()`.

See: TINKERPOP-1166, TINKERPOP-1164, TINKERPOP-951

Operational semantic test cases have been added to `GraphComputerTest` to ensure that all the above are implemented correctly.

##### Barrier Step Updates

The `Barrier` interface use to simply be a marker interface. Now it has methods and it is the primary means by which distributed steps across an OLAP job are aggregated and distributed. It is unlikely that `Barrier` was ever used directly by a provider’s custom step. Instead, a provider most likely extended `SupplyingBarrierStep`, `CollectingBarrierStep`, and/or `ReducingBarrierStep`.

Providers that have custom extensions to these steps or that use `Barrier` directly will need to adjust their implementation slightly to accommodate a new API that reflects the `Memory` updates above. This should be a simple change. Note that `FinalGet` no longer exists and such post-reduction processing is handled by the reducing step (via the new `Generating` interface).

See: TINKERPOP-1164

##### Performance Tests

The `ProcessPerformanceSuite` and `TraversalPerformanceTest` have been deprecated. They are still available, but going forward, providers should implement their own performance tests and not rely on the built-in JUnit benchmark-based performance test suite.

#### Graph Processor Providers

##### GraphFilter and GraphComputer

The `GraphComputer` API has changed with the addition of `GraphComputer.vertices(Traversal)` and `GraphComputer.edges(Traversal)`. These methods construct a `GraphFilter` object which is also new to TinkerPop 3.2.0. `GraphFilter` is a "push-down predicate" used to selectively retrieve subgraphs of the underlying graph to be OLAP processed.

- If the graph system provider relies on an existing `GraphComputer` implementations such as `SparkGraphComputer` and/or `GiraphGraphComputer`, then there is no immediate action required on their part to remain TinkerPop-compliant. However, they may wish to update their `InputFormat` or `InputRDD` implementation to be `GraphFilterAware` and handle the `GraphFilter` filtering at the disk/database level. It is advisable to do so in order to reduce OLAP load times and memory/GC usage.

- If the graph system provider has their own `GraphComputer` implementation, then they should implement the two new methods and ensure that `GraphFilter` is processed correctly. There is a new test case called `GraphComputerTest.shouldSupportGraphFilter()` which ensures the semantics of `GraphFilter` are handled correctly. For a "quick and easy" way to move forward, look to `GraphFilterInputFormat` as a way of wrapping an existing `InputFormat` to do filtering prior to `VertexProgram` or `MapReduce` execution.

Note | To quickly move forward, the `GraphComputer` implementation can simply set `GraphComputer.Features.supportsGraphFilter()` to `false` and ensure that `GraphComputer.vertices()` and `GraphComputer.edges()` throws `GraphComputer.Exceptions.graphFilterNotSupported()`. This is not recommended as its best to support `GraphFilter`.

See: TINKERPOP-962

##### Job Chaining and GraphComputer

TinkerPop 3.2.0 has integrated `VertexPrograms` into `GraphTraversal`. This means, that a single traversal can compile to multiple `GraphComputer` OLAP jobs. This requires that `ComputeResults` be chainable. There was never any explicit tests to verify if a provider’s `GraphComputer` could be chained, but now there are. Given a reasonable implementation, it is likely that no changes are required of the provider. However, to ensure the implementation is "reasonable" `GraphComputerTests` have been added.

- For providers that support their own `GraphComputer` implementation, note that there is a new `GraphComputerTest.shouldSupportJobChaining()`. This tests verifies that the `ComputerResult` output of one job can be fed into the input of a subsequent job. Only linear chains are tested/required currently. In the future, branching DAGs may be required.

- For providers that support their own `GraphComputer` implementation, note that there is a new `GraphComputerTest.shouldSupportPreExistingComputeKeys()`. When chaining OLAP jobs together, if an OLAP job requires the compute keys of a previous OLAP job, then the existing compute keys must be accessible. A simple 2 line change to `SparkGraphComputer` and `TinkerGraphComputer` solved this for TinkerPop. `GiraphGraphComputer` did not need an update as this feature was already naturally supported.

See: TINKERPOP-570

#### Graph Language Providers

##### ScriptTraversal

Providers that have custom Gremlin language implementations (e.g. Gremlin-Scala), there is a new class called `ScriptTraversal` which will handle script-based processing of traversals. The entire `GroovyXXXTest`-suite was updated to use this new class. The previous `TraversalScriptHelper` class has been deprecated so immediate upgrading is not required, but do look into `ScriptTraversal` as TinkerPop will be using it as a way to serialize "String-based traversals" over the network moving forward.

See: TINKERPOP-1154

##### ByModulating and Custom Steps

If the provider has custom steps that leverage `by()`-modulation, those will now need to implement `ByModulating`. Most of the methods in `ByModulating` are `default` and, for most situations, only `ByModulating.modulateBy(Traversal)` needs to be implemented. Note that this method’s body will most like be identical the custom step’s already existing `TraversalParent.addLocalChild()`. It is recommended that the custom step not use `TraversalParent.addLocalChild()` as this method may be deprecated in a future release. Instead, barring any complex usages, simply rename the `CustomStep.addLocalChild(Traversal)` to `CustomStep.modulateBy(Traversal)`.

See: TINKERPOP-1153

##### TraversalEngine Deprecation and GraphProvider

The `TraversalSource` infrastructure has been completely rewritten. Fortunately for users, their code is backwards compatible. Unfortunately for graph system providers, a few tweaks to their implementation are in order.

- If the graph system supports more than `Graph.compute()`, then implement `GraphProvider.getGraphComputer()`.

- For custom `TraversalStrategy` implementations, change `traverser.getEngine().isGraphComputer()` to `TraversalHelper.onGraphComputer(Traversal)`.

- For custom `Steps`, change `implements EngineDependent` to `implements GraphComputing`.

See: TINKERPOP-971

# TinkerPop 3.1.0

A 187 On The Undercover Gremlinz

## TinkerPop 3.1.8

Release Date: August 21, 2017

Please see the changelog for a complete list of all the modifications that are part of this release.

## TinkerPop 3.1.7

Release Date: June 12, 2017

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### GraphML XSLT

There were some inconsistencies in the GraphML format supported in TinkerPop 2.x. These issues were corrected on the initial release of TinkerPop 3.0.0, but as a result, attempting to read GraphML from 2.x will end with an error. A newly added XSLT file in `gremlin-core`, called `tp2-to-tp3-graphml.xslt`, transforms 2.x GraphML into 3.x GraphML, making it possible easily read in legacy GraphML through a 3.x `GraphMLReader`.

See: TINKERPOP-1608

## TinkerPop 3.1.6

Release Date: February 3, 2017

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Providers

#### Driver Providers

##### Session Close Confirmation

When a session is closed, it now returns a confirmation in the form of a single `NO CONTENT` message. When the message arrives, it means that the server has already destroyed the session. Prior to this change, the request was somewhat one-way, in that the client could send the request and the server would silently honor it. The confirmation makes it a bit easier to ensure from the client perspective that the close did what it was supposed to do, allowing the client to proceed only when the server was fully complete with its work.

See: TINKERPOP-1544

## TinkerPop 3.1.5

Release Date: October 17, 2016

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Java Driver and close()

There were a few problems noted around the `close()` of `Cluster` and `Client` instances, including issues that presented as system hangs. These issues have been resolved, however, it is worth noting that an unchecked exception that was thrown under a certain situation has changed as part of the bug fixes. When submitting an in-session request on a `Client` that was closed (or closing) an `IllegalStateException` is thrown. This replaces older functionality that threw a `ConnectionException` and relied logic far deeper in the driver to produce that error and had the potential to open additional resources despite the intention of the user to "close".

See: TINKERPOP-1467

## TinkerPop 3.1.4

Release Date: September 6, 2016

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Gremlin Server Workers

In release 3.1.3, a recommendation was made to ensure that the `threadPoolWorker` setting for Gremlin Server was no less than `2` in cases where Gremlin Server was being used with sessions that accept parallel requests. In 3.1.4, that is no longer the case and a size of `1` remains acceptable even in that specific case.

See: TINKERPOP-1350

## TinkerPop 3.1.3

Release Date: July 18, 2016

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Reserved Gremlin Server Keys

Gremlin Server has always considered certain binding keys (request parameters) as reserved, but that list has now expanded to be more inclusive all the static enums that are imported to the script engine. It is possible that those using Gremlin Server may have to rename their keys if they somehow successfully were using some of the now reserved terms in previous versions.

See: TINKERPOP-1354

#### Remote Timeout

Disabling the timeout for a `:remote` to Gremlin Server was previously accomplished by setting the timeout to `max` as in:

    :remote config timeout max

where `max` would set the timeout to be `Integer.MAX_VALUE`. While this feature is still supported, it has been deprecated in favor of the new configuration option of `none`, as in:

    :remote config timeout none

The use of `none` completely disables the timeout rather than just setting an arbitrarily high one. Note that it is still possible to get a timeout on a request if the server timeout limits are reached. The console timeout value only refers to how long the console will wait for a response from the server before giving up. By default, the timeout is set to `none`.

See: TINKERPOP-1267

#### Gremlin Server Workers

Past configuration recommendations for the `threadPoolWorker` setting on Gremlin Server stated this value could be safely set to `1` at the low end. A size of `1` is still valid for most cases, however, if Gremlin Server is being used with sessions that accept parallel requests, then this value should be no less than `2` or else certain scripts (i.e. those that block for an extended period of time) may cause Gremlin Server to lock up the session.

See: TINKERPOP-1350

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### Graph Database Providers

##### Property Keys and Hyphens

Graph providers should no longer rely on the test suite to validate that hyphens work for labels and property keys.

##### Vertex and Edge Counts

A large number of asserts for vertex and edge counts in the test suite were not being applied. This problem has been rectified, but could manifest as test errors for different implementations. The chances of the new assertions identifying previously unrecognized bugs seems slim however, as there are many other tests that validate these counts in other ways. If those were passing previously, then these new asserts should likely not pose a problem.

See: TINKERPOP-1300

##### Test Feature Annotations

A large number of `gremlin-test` feature annotations were incorrect which caused test cases to run against graphs that did not support those features. The annotations have been fixed, but this opened the possibility that more test cases will run against the graph implementation. Providers should ensure that their graph `features()` are consistent with the capabilities of the graph implementation.

See: TINKERPOP-1319

#### Graph Language Providers

##### AndTest Renaming

The `get_g_V_andXhasXage_gt_27XoutE_count_gt_2X_name` test in `AndTest` was improperly named and did not match the nature of the traversal it was providing. It has been renamed to: `get_g_V_andXhasXage_gt_27XoutE_count_gte_2X_name`.

#### Driver Providers

##### SASL Mechanism

Note that the Gremlin Driver for Java now passes a new parameter for SASL authentication called `saslMechanism`. This is an optional argument and does not represent a breaking change, but it does make the overall implementation more complete. While the default authentication implementations packaged with Gremlin Server don’t utilize this argument other implementations might, so the drivers should be able to pass it as per the SASL specification.

See: TINKERPOP-1263

## TinkerPop 3.1.2

Release Date: April 8, 2016

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Aliasing Sessions

Calls to `SessionedClient.alias()` used to throw `UnsupportedOperationException` and it was therefore not possible to use that capability with a session. That method is now properly implemented and aliasing is allowed.

See: TINKERPOP-1096

#### Remote Console

The `:remote console` command provides a way to avoid having to prefix the `:>` command to scripts when remoting. This mode of console usage can be convenient when working exclusively with a remote like Gremlin Server and there is only a desire to view the returned data and not to actually work with it locally in any way.

See: Reference Documentation - Remote Console

#### Console Remote Sessions

The `:remote tinkerpop.server` command now allows for a "session" argument to be passed to `connect`. This argument, tells the remote to configure it with a Gremlin Server session. In this way, the console can act as a window to script exception on the server and behave more like a standard "local" console when it comes to script execution.

See: TINKERPOP-1097

#### TinkerPop Archetypes

TinkerPop now offers Maven archetypes, which provide example project templates to quickly get started with TinkerPop. The available archetypes are as follows:

- `gremlin-archetype-server` - An example project that demonstrates the basic structure of a Gremlin Server project, how to connect with the Gremlin Driver, and how to embed Gremlin Server in a testing framework.

- `gremlin-archetype-tinkergraph` - A basic example of how to structure a TinkerPop project with Maven.

See: TINKERPOP-1085, Reference Documentation - Archetypes

#### Session Transaction Management

When connecting to a session with `gremlin-driver`, it is now possible to configure the `Client` instance so as to request that the server manage the transaction for each requests.

    Cluster cluster = Cluster.open();
    Client client = cluster.connect("sessionName", true);

Specifying `true` to the `connect()` method signifies that the `client` should make each request as one encapsulated in a transaction. With this configuration of `client` there is no need to close a transaction manually.

See: TINKERPOP-1039, Reference Documentation - Considering Sessions

#### Session Timeout Setting

The `gremlin-driver` now has a setting called `maxWaitForSessionClose` that allows control of how long it will wait for an in-session connection to respond to a close request before it simply times-out and moves on. When that happens, the server will either eventually close the connection via at session expiration or at the time of shutdown.

See: TINKERPOP-1160

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### All Providers

##### Provider Documentation

Documentation related to the lower-level APIs used by a provider, that was formerly in the reference documentation, has been moved to its own documentation set that is now referred to as the Provider Documentation.

See: TINKERPOP-937

#### Graph System Providers

##### GraphProvider.clear() Semantics

The semantics of the various `clear()` methods on `GraphProvider` didn’t really change, but it would be worth reviewing their implementations to ensure that implementations can be called successfully in an idempotent fashion. Multiple calls to `clear()` may occur for a single test on the same `Graph` instance, as `3.1.1-incubating` introduced an automated method for clearing graphs at the end of a test and some tests call `clear()` manually.

See: TINKERPOP-1146

#### Driver Providers

##### Session Transaction Management

Up until now transaction management has been a feature of sessionless requests only, but the new `manageTransaction` request argument for the Session OpProcessor changes that. Session-based requests can now pass this boolean value on each request to signal to Gremlin Server that it should attempt to commit (or rollback) the transaction at the end of the request. By default, this value as `false`, so there is no change to the protocol for this feature.

See: TINKERPOP-1039, Reference Documentation - Considering Sessions

##### scriptEvalTimeout Override

The Gremlin Server protocol now allows the passing of `scriptEvaluationTimeout` as an argument to the `SessionOpProcessor` and the `StandardOpProcessor`. This value will override the setting of the same name provided in the Gremlin Server configuration file on a per request basis.

#### Plugin Providers

##### RemoteAcceptor allowRemoteConsole

The `RemoteAcceptor` now has a new method called `allowRemoteConsole()`. It has a default implementation that returns `false` and should thus be a non-breaking change for current implementations. This value should only be set to `true` if the implementation expects the user to always use `:>` to interact with it. For example, the `tinkerpop.server` plugin expects all user interaction through `:>`, where the line is sent to Gremlin Server. In that case, that `RemoteAcceptor` implementation can return `true`. On the other hand, the `tinkerpop.gephi` plugin, expects that the user sometimes call `:>` and sometimes work with local evaluation as well. It interacts with the local variable bindings in the console itself. For `tinkerpop.gephi`, this method returns `false`.

See: Reference Documentation - Remote Console

## TinkerPop 3.1.1

Release Date: February 8, 2016

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Storage I/O

The `gremlin-core` io-package now has a `Storage` interface. The methods that were available via `hdfs` (e.g. `rm()`, `ls()`, `head()`, etc.) are now part of `Storage`. Both HDFS and Spark implement `Storage` via `FileSystemStorage` and `SparkContextStorage`, respectively. `SparkContextStorage` adds support for interacting with persisted RDDs in the Spark cache.

This update changed a few of the file handling methods. As it stands, these changes only effect manual Gremlin Console usage as HDFS support was previously provided via Groovy meta-programing. Thus, these are not "code-based" breaking changes.

- `hdfs.rmr()` no longer exists. `hdfs.rm()` is now recursive. Simply change all references to `rmr()` to `rm()` for identical behavior.

- `hdfs.head(location,lines,writableClass)` no longer exists.

  - For graph locations, use `hdfs.head(location,writableClass,lines)`.

  - For memory locations, use `hdfs.head(location,memoryKey,writableClass,lines)`.

- `hdfs.head(…​,ObjectWritable)` no longer exists. Use `SequenceFileInputFormat` as an input format is the parsing class.

Given that HDFS (and now Spark) interactions are possible via `Storage` and no longer via Groovy meta-programming, developers can use these `Storage` implementations in their Java code. In fact, `Storage` has greatly simplified complex file/RDD operations in both `GiraphGraphComputer` and `SparkGraphComputer`.

Finally, note that the following low-level/internal classes have been removed: `HadoopLoader` and `HDFSTools`.

See: TINKERPOP-1033, TINKERPOP-1023

#### Gremlin Server Transaction Management

Gremlin Server now has a setting called `strictTransactionManagement`, which forces the user to pass `aliases` for all requests. The aliases are then used to determine which graphs will have their transactions closed for that request. The alternative is to continue with default operations where the transactions of all configured graphs will be closed. It is likely that `strictTransactionManagement` (which is `false` by default so as to be backward compatible with previous versions) will become the future standard mode of operation for Gremlin Server as it provides a more efficient method for transaction management.

See: TINKERPOP-930, Reference Documentation - Considering Transactions

#### Deprecated credentialsDbLocation

The `credentialsDbLocation` setting was a TinkerGraph only configuration option to the `SimpleAuthenticator` for Gremlin Server. It provided the file system location to a "credentials graph" that TinkerGraph would read from a Gryo file at that spot. This setting was only required because TinkerGraph did not support file persistence at the time that `SimpleAuthenticator` was created.

As of 3.1.0-incubating, TinkerGraph received a limited persistence feature that allowed the "credentials graph" location to be specified in the TinkerGraph properties file via `gremlin.tinkergraph.graphLocation` and as such the need for `credentialsDbLocation` was eliminated.

This deprecation is not a breaking change, however users should be encouraged to convert their configurations to use the `gremlin.tinkergraph.graphLocation` as soon as possible, as the deprecated setting will be removed in a future release.

See: TINKERPOP-981, Reference Documentation - Gremlin Server Security

#### TinkerGraph Supports Any I/O

TinkerGraph’s 'gremlin.tinkergraph.graphLocation' configuration setting can now take a fully qualified class name of a `Io.Builder` implementation, which means that custom IO implementations can be used to read and write TinkerGraph instances.

See: TINKERPOP-886

#### Authenticator Method Deprecation

For users who have a custom `Authenticator` implementation for Gremlin Server, there will be a new method present:

    public default SaslNegotiator newSaslNegotiator(final InetAddress remoteAddress)

Implementation of this method is now preferred over the old method with the same name that has no arguments. The old method has been deprecated. This is a non-breaking change as the new method has a default implementation that simply calls the old deprecated method. In this way, existing `Authenticator` implementations will still work.

See: TINKERPOP-995

#### Spark Persistence Updates

Spark RDD persistence is now much safer with a "job server" system that ensures that persisted RDDs are not garbage collected by Spark. With this, the user is provider a `spark` object that enables them to manage persisted RDDs much like the `hdfs` object is used for managing files in HDFS.

Finally, `InputRDD` instance no longer need a `reduceByKey()` postfix as view merges happen prior to writing the `graphRDD`. Note that a `reduceByKey()` postfix will not cause problems if continued, it is simply inefficient and no longer required.

See: TINKERPOP-1023, TINKERPOP-1027

#### Logging

Logging to Gremlin Server and Gremlin Console can now be consistently controlled by the `log4j-server.properties` and `log4j-console.properties` which are in the respective `conf/` directories of the packaged distributions.

See: TINKERPOP-859

#### Gremlin Server Sandboxing

A number of improvements were made to the sandboxing feature of Gremlin Server (more specifically the `GremlinGroovyScriptEngine`). A new base class for sandboxing was introduce with the `AbstractSandboxExtension`, which makes it a bit easier to build white list style sandboxes. A usable implementation of this was also supplied with the `FileSandboxExtension`, which takes a configuration file containing a white list of accessible methods and variables that can be used in scripts. Note that the original `SandboxExtension` has been deprecated in favor of the `AbsstractSandboxExtension` or extending directly from Groovy’s `TypeCheckingDSL`.

See: TINKERPOP-891, Reference Documentation - Script Execution

#### Deprecated supportsAddProperty()

It was realized that `VertexPropertyFeatures.supportsAddProperty()` was effectively a duplicate of `VertexFeatures.supportsMetaProperties()`. As a result, `supportsAddProperty()` was deprecated in favor of the other. If using `supportsAddProperty()`, simply modify that code to instead utilize `supportsMetaProperties()`.

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### Graph System Providers

##### Data Types in Tests

There were a number of fixes related to usage of appropriate types in the test suite. There were cases where tests were mixing types, such that a single property key might have two different values. This mixed typing caused problems for some graphs and wasn’t really something TinkerPop was looking to explicitly enforce as a rule of implementing the interfaces.

While the changes should not have been breaking, providers should be aware that improved consistencies in the tests may present opportunities for test failures.

See: TINKERPOP-984, TINKERPOP-990, TINKERPOP-1000

#### Graph Database Providers

##### Custom ClassResolver

For providers who have built custom serializers in Gryo, there is a new feature open that can be considered. A `GryoMapper` can now take a custom Kryo `ClassResolver`, which means that custom types can be coerced to other types during serialization (e.g. a custom identifier could be serialized as a `HashMap`). The advantage to taking this approach is that users will not need to have the provider’s serializers on the client side. They will only need to exist on the server (presuming that the a type is coerced to a type available on the client, of course). The downside is that serialization is then no longer a two way street. For example, a custom `ClassResolver` that coerced a custom identifier to `HashMap` would let the client work with the identifier as a `HashMap`, but the client would then have to send that identifier back to the server as a `HashMap` where it would be recognized as a `HashMap` (not an identifier).

See: TINKERPOP-1064

##### Feature Consistency

There were a number of corrections made around the consistency of `Features` and how they were applied in tests. Corrections fell into two groups of changes:

1. Bugs in the how `Features` were applied to certain tests.

2. Refactoring around the realization that `VertexFeatures.supportsMetaProperties()` is really just a duplicate of features already exposed as `VertexPropertyFeatures.supportsAddProperty()`. `VertexPropertyFeatures.supportsAddProperty()` has been deprecated.

These changes related to "Feature Consistency" open up a number of previously non-executing tests for graphs that did not support meta-properties, so providers should be wary of potential test failure on previously non-executing tests.

See: TINKERPOP-985, TINKERPOP-997, TINKERPOP-998

#### Graph Processor Providers

##### InputRDD and OutputRDD Updates

There are two new methods on the Spark-Gremlin RDD interfaces.

- `InputRDD.readMemoryRDD()`: get a `ComputerResult.memory()` from an RDD.

- `OutputRDD.writeMemoryRDD()`: write a `ComputerResult.memory()` to an RDD.

Note that both these methods have default implementations which simply work with empty RDDs. Most providers will never need to implement these methods as they are specific to file/RDD management for `GraphComputer`. The four classes that implement these methods are `PersistedOutputRDD`, `PersistedInputRDD`, `InputFormatRDD`, and `OutputFormatRDD`. For the interested provider, study the implementations therein to see the purpose of these two new methods.

## TinkerPop 3.1.0

Release Date: November 16, 2015

Please see the changelog for a complete list of all the modifications that are part of this release.

Additional upgrade information can be found here:

- TinkerPop 3.0.2

- TinkerPop 3.0.1

### Upgrading for Users

#### Shading Jackson

The Jackson library is now shaded to `gremlin-shaded`, which will allow Jackson to version independently without breaking compatibility with dependent libraries or with those who depend on TinkerPop. The downside is that if a library depends on TinkerPop and uses the Jackson classes, those classes will no longer exist with the standard Jackson package naming. They will have to shifted as follows:

- `org.objenesis` becomes `org.apache.tinkerpop.shaded.objenesis`

- `com.esotericsoftware.minlog` becomes `org.apache.tinkerpop.shaded.minlog`

- `com.fasterxml.jackson` becomes `org.apache.tinkerpop.shaded.jackson`

See: TINKERPOP-835

#### PartitionStrategy and VertexProperty

`PartitionStrategy` now supports partitioning within `VertexProperty`. The `Graph` needs to be able to support meta-properties for this feature to work.

See: TINKERPOP-333

#### Gremlin Server and Epoll

Gremlin Server provides a configuration option to turn on support for Netty native transport on Linux, which has been shown to help improve performance.

See: TINKERPOP-901

#### Rebindings Deprecated

The notion of "rebindings" has been deprecated in favor of the term "aliases". Alias is a better and more intuitive term than rebindings which should make it easier for newcomers to understand what they are for.

See: TINKERPOP-913, Reference Documentation - Aliases

#### Configurable Driver Channelizer

The Gremlin Driver now allows the `Channerlizer` to be supplied as a configuration, which means that custom implementations may be supplied.

See: TINKERPOP-680

#### GraphSON and Strict Option

The `GraphMLReader` now has a `strict` option on the `Builder` so that if a data type for a value is invalid in some way, GraphMLReader will simply skip that problem value. In that way, it is a bit more forgiving than before especially with empty data.

See: TINKERPOP-756

#### Transaction.close() Default Behavior

The default behavior of `Transaction.close()` is to rollback the transaction. This is in contrast to previous versions where the default behavior was commit. Using rollback as the default should be thought of as a like a safer approach to closing where a user must now explicitly call `commit()` to persist their mutations.

See TINKERPOP-805 for more information.

#### ThreadLocal Transaction Settings

The `Transaction.onReadWrite()` and `Transaction.onClose()` settings now need to be set for each thread (if another behavior than the default is desired). For gremlin-server users that may be changing these settings via scripts. If the settings are changed for a sessionless request they will now only apply to that one request. If the settings are changed for an in-session request they will now only apply to all future requests made in the scope of that session.

See TINKERPOP-885

#### Hadoop-Gremlin

- Hadoop1 is no longer supported. Hadoop2 is now the only supported Hadoop version in TinkerPop.

- Spark and Giraph have been split out of Hadoop-Gremlin into their own respective packages (Spark-Gremlin and Giraph-Gremlin).

- The directory where application jars are stored in HDFS is now `hadoop-gremlin-3.2.11-libs`.

  - This versioning is important so that cross-version TinkerPop use does not cause jar conflicts.

See link:https://issues.apache.org/jira/browse/TINKERPOP-616

#### Spark-Gremlin

- Providers that wish to reuse a graphRDD can leverage the new `PersistedInputRDD` and `PersistedOutputRDD`.

  - This allows the graphRDD to avoid serialization into HDFS for reuse. Be sure to enabled persisted `SparkContext` (see documentation).

See link:https://issues.apache.org/jira/browse/TINKERPOP-868, link:https://issues.apache.org/jira/browse/TINKERPOP-925

#### TinkerGraph Serialization

TinkerGraph is serializable over Gryo, which means that it can shipped over the wire from Gremlin Server. This feature can be useful when working with remote subgraphs.

See: TINKERPOP-728

#### Deprecation in TinkerGraph

The `public static String` configurations have been renamed. The old `public static` variables have been deprecated. If the deprecated variables were being used, then convert to the replacements as soon as possible.

See: TINKERPOP-926

#### Deprecation in Gremlin-Groovy

The closure wrappers classes `GFunction`, `GSupplier`, `GConsumer` have been deprecated. In Groovy, a closure can be specified using `as Function` and thus, these wrappers are not needed. Also, the `GremlinExecutor.promoteBindings()` method which was previously deprecated has been removed.

See: TINKERPOP-879, TINKERPOP-897

#### Gephi Traversal Visualization

The process for visualizing a traversal has been simplified. There is no longer a need to "name" steps that will represent visualization points for Gephi. It is possible to just "configure" a `visualTraversal` in the console:

    gremlin> :remote config visualTraversal graph vg

which creates a special `TraversalSource` from `graph` called `vg`. The traversals created from `vg` can be used to `:submit` to Gephi.

See: Reference Documentation - Gephi

#### Alterations to GraphTraversal

There were a number of changes to `GraphTraversal`. Many of the changes came by way of deprecation, but some semantics have changed as well:

- `ConjunctionStrategy` has been renamed to `ConnectiveStrategy` (no other behaviors changed).

- `ConjunctionP` has been renamed to `ConnectiveP` (no other behaviors changed).

- `DedupBijectionStrategy` has been renamed (and made more effective) as `FilterRankingStrategy`.

- The `GraphTraversal` mutation API has change significantly with all previous methods being supported but deprecated.

  - The general pattern used now is `addE('knows').from(select('a')).to(select('b')).property('weight',1.0)`.

- The `GraphTraversal` sack API has changed with all previous methods being supported but deprecated.

  - The old `sack(mult,'weight')` is now `sack(mult).by('weight')`.

- `GroupStep` has been redesigned such that there is now only a key- and value-traversal. No more reduce-traversal.

  - The previous `group()`-methods have been renamed to `groupV3d0()`. To immediately upgrade, rename all your `group()`-calls to `groupV3d0()`.

  - To migrate to the new `group()`-methods, what was `group().by('age').by(outE()).by(sum(local))` is now `group().by('age').by(outE().sum())`.

- There was a bug in `fold()`, where if a bulked traverser was provided, the traverser was only represented once.

  - This bug fix might cause a breaking change to a user query if the non-bulk behavior was being counted on. If so, used `dedup()` prior to `fold()`.

- Both `GraphTraversal().mapKeys()` and `GraphTraversal.mapValues()` has been deprecated.

  - Use `select(keys)` and `select(columns)`. However, note that `select()` will not unroll the keys/values. Thus, `mapKeys()` ⇒ `select(keys).unfold()`.

- The data type of `Operator` enums will now always be the highest common data type of the two given numbers, rather than the data type of the first number, as it’s been before.

#### Aliasing Remotes in the Console

The `:remote` command in Gremlin Console has a new `alias` configuration option. This `alias` option allows specification of a set of key/value alias/binding pairs to apply to the remote. In this way, it becomes possible to refer to a variable on the server as something other than what it is referred to for purpose of the submitted script. For example once a `:remote` is created, this command:

    :remote alias x g

would allow "g" on the server to be referred to as "x".

    :> x.E().label().groupCount()

See: TINKERPOP-914

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

All providers should be aware that Jackson is now shaded to `gremlin-shaded` and could represent breaking change if there was usage of the dependency by way of TinkerPop, a direct dependency to Jackson may be required on the provider’s side.

#### Graph System Providers

##### GraphStep Alterations

- `GraphStep` is no longer in `sideEffect`-package, but now in `map`-package as traversals support mid-traversal `V()`.

- Traversals now support mid-traversal `V()`-steps. Graph system providers should ensure that a mid-traversal `V()` can leverage any suitable index.

See link:https://issues.apache.org/jira/browse/TINKERPOP-762

##### Decomposition of AbstractTransaction

The `AbstractTransaction` class has been abstracted into two different classes supporting two different modes of operation: `AbstractThreadLocalTransaction` and `AbstractThreadedTransaction`, where the former should be used when supporting `ThreadLocal` transactions and the latter for threaded transactions. Of course, providers may still choose to build their own implementation on `AbstractTransaction` itself or simply implement the `Transaction` interface.

The `AbstractTransaction` gains the following methods to potentially implement (though default implementations are supplied in `AbstractThreadLocalTransaction` and `AbstractThreadedTransaction`):

- `doReadWrite` that should execute the read-write consumer.

- `doClose` that should execute the close consumer.

See: TINKERPOP-765, TINKERPOP-885

##### Transaction.close() Default Behavior

The default behavior for `Transaction.close()` is to rollback the transaction and is enforced by tests, which previously asserted the opposite (i.e. commit on close). These tests have been renamed to suite the new semantics:

- `shouldCommitOnCloseByDefault` became `shouldCommitOnCloseWhenConfigured`

- `shouldRollbackOnCloseWhenConfigured` became `shouldRollbackOnCloseByDefault`

If these tests were referenced in an `OptOut`, then their names should be updated.

See: TINKERPOP-805

##### Graph Traversal Updates

There were numerous changes to the `GraphTraversal` API. Nearly all changes are backwards compatible with respective "deprecated" annotations. Please review the respective updates specified in the "Graph System Users" section.

- `GraphStep` is no longer in `sideEffect` package. Now in `map` package.

- Make sure mid-traversal `GraphStep` calls are folding `HasContainers` in for index-lookups.

- Think about copying `TinkerGraphStepStrategyTest` for your implementation so you know folding is happening correctly.

##### Element Removal

`Element.Exceptions.elementAlreadyRemoved` has been deprecated and test enforcement for consistency have been removed. Providers are free to deal with deleted elements as they see fit.

See: TINKERPOP-297

##### VendorOptimizationStrategy Rename

The `VendorOptimizationStrategy` has been renamed to `ProviderOptimizationStrategy`. This renaming is consistent with revised terminology for what were formerly referred to as "vendors".

See: TINKERPOP-876

##### GraphComputer Updates

`GraphComputer.configure(String key, Object value)` is now a method (with default implementation). This allows the user to specify engine-specific parameters to the underlying OLAP system. These parameters are not intended to be cross engine supported. Moreover, if there are not parameters that can be altered (beyond the standard `GraphComputer` methods), then the provider’s `GraphComputer` implementation should simply return and do nothing.

#### Driver Providers

##### Aliases Parameter

The "rebindings" argument to the "standard" `OpProcessor` has been renamed to "aliases". While "rebindings" is still supported it is recommended that the upgrade to "aliases" be made as soon as possible as support will be removed in the future. Gremlin Server will not accept both parameters at the same time - a request must contain either one parameter or the other if either is supplied.

See: TINKERPOP-913

##### ThreadLocal Transaction Settings

If a driver configures the `Transaction.onReadWrite()` or `Transaction.onClose()` settings, note that these settings no longer apply to all future requests. If the settings are changed for a sessionless request they will only apply to that one request. If the settings are changed from an in-session request they will only apply to all future requests made in the scope of that session.

See: TINKERPOP-885

# TinkerPop 3.0.0

A Gremlin Rāga in 7/16 Time

## TinkerPop 3.0.2

Release Date: October 19, 2015

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### BulkLoaderVertexProgram (BLVP)

`BulkLoaderVertexProgram` now supports arbitrary inputs (i addition to `HadoopGraph`, which was already supported in version 3.0.1-incubating). It can now also read from any TP3 enabled graph, like `TinkerGraph` or `Neo4jGraph`.

See: TINKERPOP-319, Reference Documentation - BLVP

#### TinkerGraph

TinkerGraph can now be configured to support persistence, where TinkerGraph will try to load a graph from a specified location and calls to `close()` will save the graph data to that location.

See: TINKERPOP-828, Reference Documentation - TinkerGraph

#### Gremlin Driver and Server

There were a number of fixes to `gremlin-driver` that prevent protocol desynchronization when talking to Gremlin Server.

On the Gremlin Server side, Websocket sub-protocol introduces a new "close" operation to explicitly close sessions. Prior to this change, sessions were closed in a more passive fashion (i.e. session timeout). There were also so bug fixes around the protocol as it pertained to third-party drivers (e.g. python) using JSON for authentication.

See: TINKERPOP-814, TINKERPOP-816, TINKERPOP-817, TINKERPOP-855, TINKERPOP-870, TINKERPOP-877

### Upgrading for Providers

#### Graph Driver Providers

##### Gremlin Server close Operation

It is important to note that this feature of the sub-protocol applies to the `SessionOpProcessor` (i.e. for session-based requests). Prior to this change, there was no way to explicitly close a session. Sessions would get closed by the server after timeout of activity. This new "op" gives drivers the ability to close the session explicitly and as needed.

See: TINKERPOP-849, Reference Documentation - OpProcessor

## TinkerPop 3.0.1

Release Date: September 2, 2015

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Gremlin Server

Gremlin Server now supports a SASL-based (Simple Authentication and Security Layer) authentication model and a default `SimpleAuthenticator` which implements the `PLAIN` SASL mechanism (i.e. plain text) to authenticate requests. This gives Gremlin Server some basic security capabilities, especially when combined with its built-in SSL feature.

There have also been changes in how global variable bindings in Gremlin Server are established via initialization scripts. The initialization scripts now allow for a `Map` of values that can be returned from those scripts. That `Map` will be used to set global bindings for the server. See this sample script for an example.

See: TINKERPOP-576

#### Neo4j

Problems related to using `:install` to get the Neo4j plugin operating in Gremlin Console on Windows have been resolved.

See: TINKERPOP-804

### Upgrading for Providers

#### Graph System Providers

##### GraphFactoryClass Annotation

Providers can consider the use of the new `GraphFactoryClass` annotation to specify the factory class that `GraphFactory` will use to open a new `Graph` instance. This is an optional feature and will generally help implementations that have an interface extending `Graph`. If that is the case, then this annotation can be used in the following fashion:

    @GraphFactory(MyGraphFactory.class)
    public interface MyGraph extends Graph{
    }

`MyGraphFactory` must contain the static `open` method that is normally expected by `GraphFactory`.

See: TINKERPOP-778

##### GraphProvider.Descriptor Annotation

There was a change that affected providers who implemented `GraphComputer` related tests such as the `ProcessComputerSuite`. If the provider runs those tests, then edit the `GraphProvider` implementation for those suites to include the `GraphProvider.Descriptor` annotation as follows:

    @GraphProvider.Descriptor(computer = GiraphGraphComputer.class)
    public final class HadoopGiraphGraphProvider extends HadoopGraphProvider {

        public GraphTraversalSource traversal(final Graph graph) {
            return GraphTraversalSource.build().engine(ComputerTraversalEngine.build().computer(GiraphGraphComputer.class)).create(graph);
        }
    }

See: TINKERPOP-690 for more information.

##### Semantics of Transaction.close()

There were some adjustments to the test suite with respect to how `Transaction.close()` was being validated. For most providers, this will generally mean checking `OptOut` annotations for test renaming problems. The error that occurs when running the test suite should make it apparent that a test name is incorrect in an `OptOut` if there are issues there.

See: TINKERPOP-764 for more information.

#### Graph Driver Providers

##### Authentication

Gremlin Server now supports SASL-based authentication. By default, Gremlin Server is not configured with authentication turned on and authentication is not required, so existing drivers should still work without any additional change. Drivers should however consider implementing this feature as it is likely that many users will want the security capabilities that it provides.

See: Reference Documentation - Gremlin Server Authentication