org.apache.lucene.facet.taxonomy.directory

## Class DirectoryTaxonomyWriter

- java.lang.Object
- - org.apache.lucene.facet.taxonomy.directory.DirectoryTaxonomyWriter

- All Implemented Interfaces:
    Closeable, AutoCloseable, TaxonomyWriter, TwoPhaseCommit

      public class DirectoryTaxonomyWriter
      extends Object
      implements TaxonomyWriter

  `TaxonomyWriter` which uses a `Directory` to store the taxonomy information on disk, and keeps an additional in-memory cache of some or all categories.

  In addition to the permanently-stored information in the `Directory`, efficiency dictates that we also keep an in-memory cache of recently seen or all categories, so that we do not need to go back to disk for every category addition to see which ordinal this category already has, if any. A `TaxonomyWriterCache` object determines the specific caching algorithm used.

  This class offers some hooks for extending classes to control the `IndexWriter` instance that is used. See `openIndexWriter(org.apache.lucene.store.Directory, org.apache.lucene.index.IndexWriterConfig)`.

  WARNING: This API is experimental and might change in incompatible ways in the next release.

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `static class` | `DirectoryTaxonomyWriter.DiskOrdinalMap` `DirectoryTaxonomyWriter.OrdinalMap` maintained on file system
    `static class` | `DirectoryTaxonomyWriter.MemoryOrdinalMap` `DirectoryTaxonomyWriter.OrdinalMap` maintained in memory
    `static interface` | `DirectoryTaxonomyWriter.OrdinalMap` Mapping from old ordinal to new ordinals, used when merging indexes with separate taxonomies.

  - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static String` | `INDEX_EPOCH` Property name of user commit data that contains the index epoch.

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `DirectoryTaxonomyWriter(Directory d)` Create this with `OpenMode.CREATE_OR_APPEND`.
    `DirectoryTaxonomyWriter(Directory directory, IndexWriterConfig.OpenMode openMode)` Creates a new instance with a default cache as defined by `defaultTaxonomyWriterCache()`.
    `DirectoryTaxonomyWriter(Directory directory, IndexWriterConfig.OpenMode openMode, TaxonomyWriterCache cache)` Construct a Taxonomy writer.

  - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `int` | `addCategory(FacetLabel categoryPath)` addCategory() adds a category with a given path name to the taxonomy, and returns its ordinal.
    `void` | `addTaxonomy(Directory taxoDir, DirectoryTaxonomyWriter.OrdinalMap map)` Takes the categories from the given taxonomy directory, and adds the missing ones to this taxonomy.
    `void` | `close()` Frees used resources as well as closes the underlying `IndexWriter`, which commits whatever changes made to it to the underlying `Directory`.
    `protected void` | `closeResources()` A hook for extending classes to close additional resources that were used.
    `long` | `commit()`
    `protected IndexWriterConfig` | `createIndexWriterConfig(IndexWriterConfig.OpenMode openMode)` Create the `IndexWriterConfig` that would be used for opening the internal index writer.
    `static TaxonomyWriterCache` | `defaultTaxonomyWriterCache()` Defines the default `TaxonomyWriterCache` to use in constructors which do not specify one.
    `protected void` | `ensureOpen()` Verifies that this instance wasn't closed, or throws `AlreadyClosedException` if it is.
    `protected int` | `findCategory(FacetLabel categoryPath)` Look up the given category in the cache and/or the on-disk storage, returning the category's ordinal, or a negative number in case the category does not yet exist in the taxonomy.
    `TaxonomyWriterCache` | `getCache()` Returns the `TaxonomyWriterCache` in use by this writer.
    `Directory` | `getDirectory()` Returns the `Directory` of this taxonomy writer.
    `Iterable<Map.Entry<String,String>>` | `getLiveCommitData()` Returns the commit user data iterable that was set on `TaxonomyWriter.setLiveCommitData(Iterable)`.
    `int` | `getParent(int ordinal)` getParent() returns the ordinal of the parent category of the category with the given ordinal.
    `int` | `getSize()` getSize() returns the number of categories in the taxonomy.
    `long` | `getTaxonomyEpoch()` Expert: returns current index epoch, if this is a near-real-time reader.
    `protected IndexWriter` | `openIndexWriter(Directory directory, IndexWriterConfig config)` Open internal index writer, which contains the taxonomy data.
    `long` | `prepareCommit()` prepare most of the work needed for a two-phase commit.
    `void` | `replaceTaxonomy(Directory taxoDir)` Replaces the current taxonomy with the given one.
    `void` | `rollback()` Rollback changes to the taxonomy writer and closes the instance.
    `void` | `setCacheMissesUntilFill(int i)` Set the number of cache misses before an attempt is made to read the entire taxonomy into the in-memory cache.
    `void` | `setLiveCommitData(Iterable<Map.Entry<String,String>> commitUserData)` Sets the commit user data iterable.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### INDEX_EPOCH

          public static final String INDEX_EPOCH

      Property name of user commit data that contains the index epoch. The epoch changes whenever the taxonomy is recreated (i.e. opened with `IndexWriterConfig.OpenMode.CREATE`.

      Applications should not use this property in their commit data because it will be overridden by this taxonomy writer.

      See Also:
        Constant Field Values

  - ### Constructor Detail

    - #### DirectoryTaxonomyWriter

          public DirectoryTaxonomyWriter(Directory directory,
                                         IndexWriterConfig.OpenMode openMode,
                                         TaxonomyWriterCache cache)
                                  throws IOException

      Construct a Taxonomy writer.
      Parameters:
        `directory` - The `Directory` in which to store the taxonomy. Note that the taxonomy is written directly to that directory (not to a subdirectory of it).
        `openMode` - Specifies how to open a taxonomy for writing: `APPEND` means open an existing index for append (failing if the index does not yet exist). `CREATE` means create a new index (first deleting the old one if it already existed). `APPEND_OR_CREATE` appends to an existing index if there is one, otherwise it creates a new index.
        `cache` - A `TaxonomyWriterCache` implementation which determines the in-memory caching policy. See for example `LruTaxonomyWriterCache` and `UTF8TaxonomyWriterCache`. If null or missing, `defaultTaxonomyWriterCache()` is used.
      Throws:
        `CorruptIndexException` - if the taxonomy is corrupted.
        `LockObtainFailedException` - if the taxonomy is locked by another writer.
        `IOException` - if another error occurred.

    - #### DirectoryTaxonomyWriter

          public DirectoryTaxonomyWriter(Directory directory,
                                         IndexWriterConfig.OpenMode openMode)
                                  throws IOException

      Creates a new instance with a default cache as defined by `defaultTaxonomyWriterCache()`.
      Throws:
        `IOException`

    - #### DirectoryTaxonomyWriter

          public DirectoryTaxonomyWriter(Directory d)
                                  throws IOException

      Create this with `OpenMode.CREATE_OR_APPEND`.
      Throws:
        `IOException`

  - ### Method Detail

    - #### getCache

          public TaxonomyWriterCache getCache()

      Returns the `TaxonomyWriterCache` in use by this writer.

    - #### openIndexWriter

          protected IndexWriter openIndexWriter(Directory directory,
                                                IndexWriterConfig config)
                                         throws IOException

      Open internal index writer, which contains the taxonomy data.

      Extensions may provide their own `IndexWriter` implementation or instance.
      NOTE: the instance this method returns will be closed upon calling to `close()`.
      NOTE: the merge policy in effect must not merge none adjacent segments. See comment in `createIndexWriterConfig(IndexWriterConfig.OpenMode)` for the logic behind this.

      Parameters:
        `directory` - the `Directory` on top of which an `IndexWriter` should be opened.
        `config` - configuration for the internal index writer.
      Throws:
        `IOException`
      See Also:
        `createIndexWriterConfig(IndexWriterConfig.OpenMode)`

    - #### createIndexWriterConfig

          protected IndexWriterConfig createIndexWriterConfig(IndexWriterConfig.OpenMode openMode)

      Create the `IndexWriterConfig` that would be used for opening the internal index writer.
      Extensions can configure the `IndexWriter` as they see fit, including setting a `merge-scheduler`, or `deletion-policy`, different RAM size etc.
      NOTE: internal docids of the configured index must not be altered. For that, categories are never deleted from the taxonomy index. In addition, merge policy in effect must not merge none adjacent segments.
      Parameters:
        `openMode` - see `IndexWriterConfig.OpenMode`
      See Also:
        `openIndexWriter(Directory, IndexWriterConfig)`

    - #### defaultTaxonomyWriterCache

          public static TaxonomyWriterCache defaultTaxonomyWriterCache()

      Defines the default `TaxonomyWriterCache` to use in constructors which do not specify one.

      The current default is `UTF8TaxonomyWriterCache`, i.e., the entire taxonomy is cached in memory while building it.

    - #### close

          public void close()
                     throws IOException

      Frees used resources as well as closes the underlying `IndexWriter`, which commits whatever changes made to it to the underlying `Directory`.
      Specified by:
        `close` in interface `Closeable`
      Specified by:
        `close` in interface `AutoCloseable`
      Throws:
        `IOException`

    - #### closeResources

          protected void closeResources()
                                 throws IOException

      A hook for extending classes to close additional resources that were used. The default implementation closes the `IndexReader` as well as the `TaxonomyWriterCache` instances that were used.
      NOTE: if you override this method, you should include a `super.closeResources()` call in your implementation.
      Throws:
        `IOException`

    - #### findCategory

          protected int findCategory(FacetLabel categoryPath)
                              throws IOException

      Look up the given category in the cache and/or the on-disk storage, returning the category's ordinal, or a negative number in case the category does not yet exist in the taxonomy.
      Throws:
        `IOException`

    - #### addCategory

          public int addCategory(FacetLabel categoryPath)
                          throws IOException

      Description copied from interface: `TaxonomyWriter`
      addCategory() adds a category with a given path name to the taxonomy, and returns its ordinal. If the category was already present in the taxonomy, its existing ordinal is returned.

      Before adding a category, addCategory() makes sure that all its ancestor categories exist in the taxonomy as well. As result, the ordinal of a category is guaranteed to be smaller then the ordinal of any of its descendants.

      Specified by:
        `addCategory` in interface `TaxonomyWriter`
      Throws:
        `IOException`

    - #### ensureOpen

          protected final void ensureOpen()

      Verifies that this instance wasn't closed, or throws `AlreadyClosedException` if it is.

    - #### commit

          public long commit()
                      throws IOException

      Specified by:
        `commit` in interface `TwoPhaseCommit`
      Throws:
        `IOException`

    - #### setLiveCommitData

          public void setLiveCommitData(Iterable<Map.Entry<String,String>> commitUserData)

      Description copied from interface: `TaxonomyWriter`
      Sets the commit user data iterable. See `IndexWriter.setLiveCommitData(java.lang.Iterable<java.util.Map.Entry<java.lang.String, java.lang.String>>)`.
      Specified by:
        `setLiveCommitData` in interface `TaxonomyWriter`

    - #### getLiveCommitData

          public Iterable<Map.Entry<String,String>> getLiveCommitData()

      Description copied from interface: `TaxonomyWriter`
      Returns the commit user data iterable that was set on `TaxonomyWriter.setLiveCommitData(Iterable)`.
      Specified by:
        `getLiveCommitData` in interface `TaxonomyWriter`

    - #### prepareCommit

          public long prepareCommit()
                             throws IOException

      prepare most of the work needed for a two-phase commit. See `IndexWriter.prepareCommit()`.
      Specified by:
        `prepareCommit` in interface `TwoPhaseCommit`
      Throws:
        `IOException`

    - #### getSize

          public int getSize()

      Description copied from interface: `TaxonomyWriter`
      getSize() returns the number of categories in the taxonomy.

      Because categories are numbered consecutively starting with 0, it means the taxonomy contains ordinals 0 through getSize()-1.

      Note that the number returned by getSize() is often slightly higher than the number of categories inserted into the taxonomy; This is because when a category is added to the taxonomy, its ancestors are also added automatically (including the root, which always get ordinal 0).

      Specified by:
        `getSize` in interface `TaxonomyWriter`

    - #### setCacheMissesUntilFill

          public void setCacheMissesUntilFill(int i)

      Set the number of cache misses before an attempt is made to read the entire taxonomy into the in-memory cache.

      This taxonomy writer holds an in-memory cache of recently seen categories to speed up operation. On each cache-miss, the on-disk index needs to be consulted. When an existing taxonomy is opened, a lot of slow disk reads like that are needed until the cache is filled, so it is more efficient to read the entire taxonomy into memory at once. We do this complete read after a certain number (defined by this method) of cache misses.

      If the number is set to `0`, the entire taxonomy is read into the cache on first use, without fetching individual categories first.

      NOTE: it is assumed that this method is called immediately after the taxonomy writer has been created.

    - #### getParent

          public int getParent(int ordinal)
                        throws IOException

      Description copied from interface: `TaxonomyWriter`
      getParent() returns the ordinal of the parent category of the category with the given ordinal.

      When a category is specified as a path name, finding the path of its parent is as trivial as dropping the last component of the path. getParent() is functionally equivalent to calling getPath() on the given ordinal, dropping the last component of the path, and then calling getOrdinal() to get an ordinal back.

      If the given ordinal is the ROOT_ORDINAL, an INVALID_ORDINAL is returned. If the given ordinal is a top-level category, the ROOT_ORDINAL is returned. If an invalid ordinal is given (negative or beyond the last available ordinal), an IndexOutOfBoundsException is thrown. However, it is expected that getParent will only be called for ordinals which are already known to be in the taxonomy. TODO (Facet): instead of a getParent(ordinal) method, consider having a

      getCategory(categorypath, prefixlen) which is similar to addCategory except it doesn't add new categories; This method can be used to get the ordinals of all prefixes of the given category, and it can use exactly the same code and cache used by addCategory() so it means less code.

      Specified by:
        `getParent` in interface `TaxonomyWriter`
      Throws:
        `IOException`

    - #### addTaxonomy

          public void addTaxonomy(Directory taxoDir,
                                  DirectoryTaxonomyWriter.OrdinalMap map)
                           throws IOException

      Takes the categories from the given taxonomy directory, and adds the missing ones to this taxonomy. Additionally, it fills the given `DirectoryTaxonomyWriter.OrdinalMap` with a mapping from the original ordinal to the new ordinal.
      Throws:
        `IOException`

    - #### rollback

          public void rollback()
                        throws IOException

      Rollback changes to the taxonomy writer and closes the instance. Following this method the instance becomes unusable (calling any of its API methods will yield an `AlreadyClosedException`).
      Specified by:
        `rollback` in interface `TwoPhaseCommit`
      Throws:
        `IOException`

    - #### replaceTaxonomy

          public void replaceTaxonomy(Directory taxoDir)
                               throws IOException

      Replaces the current taxonomy with the given one. This method should generally be called in conjunction with `IndexWriter.addIndexes(Directory...)` to replace both the taxonomy as well as the search index content.
      Throws:
        `IOException`

    - #### getDirectory

          public Directory getDirectory()

      Returns the `Directory` of this taxonomy writer.

    - #### getTaxonomyEpoch

          public final long getTaxonomyEpoch()

      Expert: returns current index epoch, if this is a near-real-time reader. Used by `DirectoryTaxonomyReader` to support NRT.
      NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

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