Change defaults in IndexWriter to maximize "out of the box" performance
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Key: LUCENE-994
URL: https://issues.apache.org/jira/browse/LUCENE-994
Project: Lucene - Java
Issue Type: Improvement
Components: Index
Affects Versions: 2.3
Reporter: Michael McCandless
Assignee: Michael McCandless
Priority: Minor
Fix For: 2.3
This is follow-through from LUCENE-845, LUCENE-847 and LUCENE-870;
I'll commit this once those three are committed.
Out of the box performance of IndexWriter is maximized when flushing
by RAM instead of a fixed document count (the default today) because
documents can vary greatly in size.
Likewise, merging performance should be faster when merging by net
segment size since, to minimize the net IO cost of merging segments
over time, you want to merge segments of equal byte size.
Finally, ConcurrentMergeScheduler improves indexing speed
substantially (25% in a simple initial test in LUCENE-870) because it
runs the merges in the backround and doesn't block
add/update/deleteDocument calls. Most machines have concurrency
between CPU and IO and so it makes sense to default to this
MergeScheduler.
Note that these changes will break users of ParallelReader because the
parallel indices will no longer have matching docIDs. Such users need
to switch IndexWriter back to flushing by doc count, and switch the
MergePolicy back to LogDocMergePolicy. It's likely also necessary to
switch the MergeScheduler back to SerialMergeScheduler to ensure
deterministic docID assignment.
I think the combination of these three default changes, plus other
performance improvements for indexing (LUCENE-966, LUCENE-843,
LUCENE-963, LUCENE-969, LUCENE-871, etc.) should make for some sizable
performance gains Lucene 2.3!
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