org.apache.lucene.replicator

## Class IndexReplicationHandler

- java.lang.Object
- - org.apache.lucene.replicator.IndexReplicationHandler

- All Implemented Interfaces:
    ReplicationClient.ReplicationHandler

      public class IndexReplicationHandler
      extends Object
      implements ReplicationClient.ReplicationHandler

  A `ReplicationClient.ReplicationHandler` for replication of an index. Implements `revisionReady(java.lang.String, java.util.Map<java.lang.String, java.util.List<org.apache.lucene.replicator.RevisionFile>>, java.util.Map<java.lang.String, java.util.List<java.lang.String>>, java.util.Map<java.lang.String, org.apache.lucene.store.Directory>)` by copying the files pointed by the client resolver to the index `Directory` and then touches the index with `IndexWriter` to make sure any unused files are deleted.

  NOTE: this handler assumes that `IndexWriter` is not opened by another process on the index directory. In fact, opening an `IndexWriter` on the same directory to which files are copied can lead to undefined behavior, where some or all the files will be deleted, override other files or simply create a mess. When you replicate an index, it is best if the index is never modified by `IndexWriter`, except the one that is open on the source index, from which you replicate.

  This handler notifies the application via a provided `Callable` when an updated index commit was made available for it.

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

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static String` | `INFO_STREAM_COMPONENT` The component used to log messages to the `default` `InfoStream`.

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `IndexReplicationHandler(Directory indexDir, Callable<Boolean> callback)` Constructor with the given index directory and callback to notify when the indexes were updated.

  - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `static void` | `cleanupFilesOnFailure(Directory dir, List<String> files)` Cleanup the index directory by deleting all given files.
    `static void` | `cleanupOldIndexFiles(Directory dir, String segmentsFile, InfoStream infoStream)` Cleans up the index directory from old index files.
    `static void` | `copyFiles(Directory source, Directory target, List<String> files)` Copies the files from the source directory to the target one, if they are not the same.
    `Map<String,List<RevisionFile>>` | `currentRevisionFiles()` Returns the current revision files held by the handler.
    `String` | `currentVersion()` Returns the current revision version held by the handler.
    `static IndexCommit` | `getLastCommit(Directory dir)` Returns the last `IndexCommit` found in the `Directory`, or `null` if there are no commits.
    `static String` | `getSegmentsFile(List<String> files, boolean allowEmpty)` Verifies that the last file is segments_N and fails otherwise.
    `void` | `revisionReady(String version, Map<String,List<RevisionFile>> revisionFiles, Map<String,List<String>> copiedFiles, Map<String,Directory> sourceDirectory)` Called when a new revision was obtained and is available (i.e.
    `void` | `setInfoStream(InfoStream infoStream)` Sets the `InfoStream` to use for logging messages.

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

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

- - ### Field Detail

    - #### INFO_STREAM_COMPONENT

          public static final String INFO_STREAM_COMPONENT

      The component used to log messages to the `default` `InfoStream`.
      See Also:
        Constant Field Values

  - ### Constructor Detail

    - #### IndexReplicationHandler

          public IndexReplicationHandler(Directory indexDir,
                                         Callable<Boolean> callback)
                                  throws IOException

      Constructor with the given index directory and callback to notify when the indexes were updated.
      Throws:
        `IOException`

  - ### Method Detail

    - #### getLastCommit

          public static IndexCommit getLastCommit(Directory dir)
                                           throws IOException

      Returns the last `IndexCommit` found in the `Directory`, or `null` if there are no commits.
      Throws:
        `IOException`

    - #### getSegmentsFile

          public static String getSegmentsFile(List<String> files,
                                               boolean allowEmpty)

      Verifies that the last file is segments_N and fails otherwise. It also removes and returns the file from the list, because it needs to be handled last, after all files. This is important in order to guarantee that if a reader sees the new segments_N, all other segment files are already on stable storage.

      The reason why the code fails instead of putting segments_N file last is that this indicates an error in the Revision implementation.

    - #### cleanupFilesOnFailure

          public static void cleanupFilesOnFailure(Directory dir,
                                                   List<String> files)

      Cleanup the index directory by deleting all given files. Called when file copy or sync failed.

    - #### cleanupOldIndexFiles

          public static void cleanupOldIndexFiles(Directory dir,
                                                  String segmentsFile,
                                                  InfoStream infoStream)

      Cleans up the index directory from old index files. This method uses the last commit found by `getLastCommit(Directory)`. If it matches the expected segmentsFile, then all files not referenced by this commit point are deleted.

      NOTE: this method does a best effort attempt to clean the index directory. It suppresses any exceptions that occur, as this can be retried the next time.

    - #### copyFiles

          public static void copyFiles(Directory source,
                                       Directory target,
                                       List<String> files)
                                throws IOException

      Copies the files from the source directory to the target one, if they are not the same.
      Throws:
        `IOException`

    - #### currentVersion

          public String currentVersion()

      Description copied from interface: `ReplicationClient.ReplicationHandler`
      Returns the current revision version held by the handler.
      Specified by:
        `currentVersion` in interface `ReplicationClient.ReplicationHandler`

    - #### currentRevisionFiles

          public Map<String,List<RevisionFile>> currentRevisionFiles()

      Description copied from interface: `ReplicationClient.ReplicationHandler`
      Returns the current revision files held by the handler.
      Specified by:
        `currentRevisionFiles` in interface `ReplicationClient.ReplicationHandler`

    - #### revisionReady

          public void revisionReady(String version,
                                    Map<String,List<RevisionFile>> revisionFiles,
                                    Map<String,List<String>> copiedFiles,
                                    Map<String,Directory> sourceDirectory)
                             throws IOException

      Description copied from interface: `ReplicationClient.ReplicationHandler`
      Called when a new revision was obtained and is available (i.e. all needed files were successfully copied).
      Specified by:
        `revisionReady` in interface `ReplicationClient.ReplicationHandler`
      Parameters:
        `version` - the version of the `Revision` that was copied
        `revisionFiles` - the files contained by this `Revision`
        `copiedFiles` - the files that were actually copied
        `sourceDirectory` - a mapping from a source of files to the `Directory` they were copied into
      Throws:
        `IOException`

    - #### setInfoStream

          public void setInfoStream(InfoStream infoStream)

      Sets the `InfoStream` to use for logging messages.

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