Some improvements to CMS
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Key: LUCENE-2755
URL: https://issues.apache.org/jira/browse/LUCENE-2755
Project: Lucene - Java
Issue Type: Improvement
Components: Index
Reporter: Shai Erera
Assignee: Shai Erera
Priority: Minor
Fix For: 3.1, 4.0
While running optimize on a large index, I've noticed several things that got
me to read CMS code more carefully, and find these issues:
* CMS may hold onto a merge if maxMergeCount is hit. That results in the
MergeThreads taking merges from the IndexWriter until they are exhausted, and
only then that blocked merge will run. I think it's unnecessary that that merge
will be blocked.
* CMS sorts merges by segments size, doc-based and not bytes-based. Since the
default MP is LogByteSizeMP, and I hardly believe people care about doc-based
size segments anymore, I think we should switch the default impl. There are two
ways to make it extensible, if we want:
** Have an overridable member/method in CMS that you can extend and override -
easy.
** Have OneMerge be comparable and let the MP determine the order (e.g. by
bytes, docs, calibrate deletes etc.). Better, but will need to tap into several
places in the code, so more risky and complicated.
On the go, I'd like to add some documentation to CMS - it's not very easy to
read and follow.
I'll work on a patch.
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