Class UpgradeIndexMergePolicy

  • All Implemented Interfaces:

    public class UpgradeIndexMergePolicy
    extends FilterMergePolicy
    This MergePolicy is used for upgrading all existing segments of an index when calling IndexWriter.forceMerge(int). All other methods delegate to the base MergePolicy given to the constructor. This allows for an as-cheap-as possible upgrade of an older index by only upgrading segments that are created by previous Lucene versions. forceMerge does no longer really merge; it is just used to "forceMerge" older segment versions away.

    In general one would use IndexUpgrader, but for a fully customizeable upgrade, you can use this like any other MergePolicy and call IndexWriter.forceMerge(int):

      IndexWriterConfig iwc = new IndexWriterConfig(Version.LUCENE_XX, new KeywordAnalyzer());
      iwc.setMergePolicy(new UpgradeIndexMergePolicy(iwc.getMergePolicy()));
      IndexWriter w = new IndexWriter(dir, iwc);

    Warning: This merge policy may reorder documents if the index was partially upgraded before calling forceMerge (e.g., documents were added). If your application relies on "monotonicity" of doc IDs (which means that the order in which the documents were added to the index is preserved), do a forceMerge(1) instead. Please note, the delegate MergePolicy may also reorder documents.

    See Also:
    WARNING: This API is experimental and might change in incompatible ways in the next release.
    • Constructor Detail

      • UpgradeIndexMergePolicy

        public UpgradeIndexMergePolicy​(MergePolicy in)
        Wrap the given MergePolicy and intercept forceMerge requests to only upgrade segments written with previous Lucene versions.
    • Method Detail

      • shouldUpgradeSegment

        protected boolean shouldUpgradeSegment​(SegmentCommitInfo si)
        Returns if the given segment should be upgraded. The default implementation will return !Version.LATEST.equals(si.getVersion()), so all segments created with a different version number than this Lucene version will get upgraded.
      • 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.
        findForcedMerges in class FilterMergePolicy
        segmentInfos - the total set of segments in the index
        maxSegmentCount - requested maximum number of segments in the index
        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