UpgradeIndexMergePolicy
This MergePolicy is used for upgrading all existing segments of an index when calling IndexWriter.forceMerge. 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:
IndexWriterConfig iwc = new IndexWriterConfig(Version.LUCENE_XX, new KeywordAnalyzer()); iwc.setMergePolicy(new UpgradeIndexMergePolicy(iwc.getMergePolicy())); IndexWriter w = new IndexWriter(dir, iwc); w.forceMerge(1); w.close();*
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
Functions
Determine what set of merge operations is necessary in order to expunge all deletes from the index.
Determine what set of merge operations is necessary in order to merge to <= the specified segment count. IndexWriter calls this when its IndexWriter.forceMerge method is called. This call is always synchronized on the IndexWriter instance so only one thread at a time will call this method.
Identifies merges that we want to execute (synchronously) on commit. By default, this will return .findMerges whose segments are all less than the .maxFullFlushMergeSize.
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.
Returns true if the segment represented by the given CodecReader should be kept even if it's fully deleted. This is useful for testing of for instance if the merge policy implements retention policies for soft deletes.
Return the maximum size of segments to be included in full-flush merges by the default implementation of .findFullFlushMerges.
Returns the number of deletes that a merge would claim on the given segment. This method will by default return the sum of the del count on disk and the pending delete count. Yet, subclasses that wrap merge readers might modify this to reflect deletes that are carried over to the target segment in the case of soft deletes.
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.
Return the byte size of the provided SegmentCommitInfo, prorated by percentage of non-deleted documents.
Unwraps this instance
Returns true if a new segment (regardless of its origin) should use the compound file format. The default implementation returns true iff the size of the given mergedInfo is less or equal to .getMaxCFSSegmentSizeMB and the size is less or equal to the TotalIndexSize * .getNoCFSRatio otherwise false.