org.apache.lucene.index

## Class OneMergeWrappingMergePolicy

- java.lang.Object
- - org.apache.lucene.index.MergePolicy
  - - org.apache.lucene.index.FilterMergePolicy
    - - org.apache.lucene.index.OneMergeWrappingMergePolicy

- Direct Known Subclasses:
    SoftDeletesRetentionMergePolicy

      public class OneMergeWrappingMergePolicy
      extends FilterMergePolicy

  A wrapping merge policy that wraps the `MergePolicy.OneMerge` objects returned by the wrapped merge policy.
  WARNING: This API is experimental and might change in incompatible ways in the next release.

- - ### Nested Class Summary

    - ### Nested classes/interfaces inherited from class org.apache.lucene.index.MergePolicy

      `MergePolicy.MergeAbortedException, MergePolicy.MergeContext, MergePolicy.MergeException, MergePolicy.MergeSpecification, MergePolicy.OneMerge, MergePolicy.OneMergeProgress`

  - ### Field Summary

    - ### Fields inherited from class org.apache.lucene.index.FilterMergePolicy

      `in`

    - ### Fields inherited from class org.apache.lucene.index.MergePolicy

      `DEFAULT_MAX_CFS_SEGMENT_SIZE, DEFAULT_NO_CFS_RATIO, maxCFSSegmentSize, noCFSRatio`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `OneMergeWrappingMergePolicy(MergePolicy in, UnaryOperator<MergePolicy.OneMerge> wrapOneMerge)` Constructor

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `MergePolicy.MergeSpecification` | `findForcedDeletesMerges(SegmentInfos segmentInfos, MergePolicy.MergeContext mergeContext)` Determine what set of merge operations is necessary in order to expunge all deletes from the index.
    `MergePolicy.MergeSpecification` | `findForcedMerges(SegmentInfos segmentInfos, int maxSegmentCount, Map<SegmentCommitInfo,Boolean> segmentsToMerge, MergePolicy.MergeContext mergeContext)` Determine what set of merge operations is necessary in order to merge to `<=` the specified segment count.
    `MergePolicy.MergeSpecification` | `findFullFlushMerges(MergeTrigger mergeTrigger, SegmentInfos segmentInfos, MergePolicy.MergeContext mergeContext)` Identifies merges that we want to execute (synchronously) on commit.
    `MergePolicy.MergeSpecification` | `findMerges(MergeTrigger mergeTrigger, SegmentInfos segmentInfos, MergePolicy.MergeContext mergeContext)` Determine what set of merge operations are now necessary on the index.

    - ### Methods inherited from class org.apache.lucene.index.FilterMergePolicy

      `getMaxCFSSegmentSizeMB, getNoCFSRatio, keepFullyDeletedSegment, numDeletesToMerge, setMaxCFSSegmentSizeMB, setNoCFSRatio, size, toString, useCompoundFile`

    - ### Methods inherited from class org.apache.lucene.index.MergePolicy

      `assertDelCount, isMerged, message, segString, verbose`

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

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

- - ### Constructor Detail

    - #### OneMergeWrappingMergePolicy

          public OneMergeWrappingMergePolicy(MergePolicy in,
                                             UnaryOperator<MergePolicy.OneMerge> wrapOneMerge)

      Constructor
      Parameters:
        `in` - - the wrapped merge policy
        `wrapOneMerge` - - operator for wrapping OneMerge objects

  - ### Method Detail

    - #### findMerges

          public MergePolicy.MergeSpecification findMerges(MergeTrigger mergeTrigger,
                                                           SegmentInfos segmentInfos,
                                                           MergePolicy.MergeContext mergeContext)
                                                    throws IOException

      Description copied from class: `MergePolicy`
      Determine what set of merge operations are now necessary on the index. `IndexWriter` calls this whenever there is a change to the segments. This call is always synchronized on the `IndexWriter` instance so only one thread at a time will call this method.
      Overrides:
        `findMerges` in class `FilterMergePolicy`
      Parameters:
        `mergeTrigger` - the event that triggered the merge
        `segmentInfos` - the total set of segments in the index
        `mergeContext` - the IndexWriter to find the merges on
      Throws:
        `IOException`

    - #### findForcedMerges

          public MergePolicy.MergeSpecification findForcedMerges(SegmentInfos segmentInfos,
                                                                 int maxSegmentCount,
                                                                 Map<SegmentCommitInfo,Boolean> segmentsToMerge,
                                                                 MergePolicy.MergeContext mergeContext)
                                                          throws IOException

      Description copied from class: `MergePolicy`
      Determine what set of merge operations is necessary in order to merge to `<=` the specified segment count. `IndexWriter` calls this when its `IndexWriter.forceMerge(int)` method is called. This call is always synchronized on the `IndexWriter` instance so only one thread at a time will call this method.
      Overrides:
        `findForcedMerges` in class `FilterMergePolicy`
      Parameters:
        `segmentInfos` - the total set of segments in the index
        `maxSegmentCount` - requested maximum number of segments in the index (currently this is always 1)
        `segmentsToMerge` - contains the specific SegmentInfo instances that must be merged away. This may be a subset of all SegmentInfos. If the value is True for a given SegmentInfo, that means this segment was an original segment present in the to-be-merged index; else, it was a segment produced by a cascaded merge.
        `mergeContext` - the MergeContext to find the merges on
      Throws:
        `IOException`

    - #### findForcedDeletesMerges

          public MergePolicy.MergeSpecification findForcedDeletesMerges(SegmentInfos segmentInfos,
                                                                        MergePolicy.MergeContext mergeContext)
                                                                 throws IOException

      Description copied from class: `MergePolicy`
      Determine what set of merge operations is necessary in order to expunge all deletes from the index.
      Overrides:
        `findForcedDeletesMerges` in class `FilterMergePolicy`
      Parameters:
        `segmentInfos` - the total set of segments in the index
        `mergeContext` - the MergeContext to find the merges on
      Throws:
        `IOException`

    - #### findFullFlushMerges

          public MergePolicy.MergeSpecification findFullFlushMerges(MergeTrigger mergeTrigger,
                                                                    SegmentInfos segmentInfos,
                                                                    MergePolicy.MergeContext mergeContext)
                                                             throws IOException

      Description copied from class: `MergePolicy`
      Identifies merges that we want to execute (synchronously) on commit. By default, this will do no merging on commit. If you implement this method in your `MergePolicy` you must also set a non-zero timeout using `IndexWriterConfig.setMaxCommitMergeWaitMillis(long)`. Any merges returned here will make `IndexWriter.commit()` or `IndexWriter.prepareCommit()` block until the merges complete or until `LiveIndexWriterConfig.getMaxCommitMergeWaitMillis()` has elapsed. This may be used to merge small segments that have just been flushed as part of the commit, reducing the number of segments in the commit. If a merge does not complete in the allotted time, it will continue to execute, and eventually finish and apply to future commits, but will not be reflected in the current commit. If a `MergePolicy.OneMerge` in the returned `MergePolicy.MergeSpecification` includes a segment already included in a registered merge, then `IndexWriter.commit()` or `IndexWriter.prepareCommit()` will throw a `IllegalStateException`. Use `MergePolicy.MergeContext.getMergingSegments()` to determine which segments are currently registered to merge.
      Overrides:
        `findFullFlushMerges` in class `FilterMergePolicy`
      Parameters:
        `mergeTrigger` - the event that triggered the merge (COMMIT or FULL_FLUSH).
        `segmentInfos` - the total set of segments in the index (while preparing the commit)
        `mergeContext` - the MergeContext to find the merges on, which should be used to determine which segments are already in a registered merge (see `MergePolicy.MergeContext.getMergingSegments()`).
      Throws:
        `IOException`

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