Use parallel arrays instead of PostingList objects
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Key: LUCENE-2329
URL: https://issues.apache.org/jira/browse/LUCENE-2329
Project: Lucene - Java
Issue Type: Improvement
Components: Index
Reporter: Michael Busch
Assignee: Michael Busch
Priority: Minor
Fix For: 3.1
This is Mike's idea that was discussed in LUCENE-2293 and LUCENE-2324.
In order to avoid having very many long-living PostingList objects in
TermsHashPerField we want to switch to parallel arrays. The termsHash will
simply be a int[] which maps each term to dense termIDs.
All data that the PostingList classes currently hold will then we placed in
parallel arrays, where the termID is the index into the arrays. This will
avoid the need for object pooling, will remove the overhead of object
initialization and garbage collection. Especially garbage collection should
benefit significantly when the JVM runs out of memory, because in such a
situation the gc mark times can get very long if there is a big number of
long-living objects in memory.
Another benefit could be to build more efficient TermVectors. We could avoid
the need of having to store the term string per document in the TermVector.
Instead we could just store the segment-wide termIDs. This would reduce the
size and also make it easier to implement efficient algorithms that use
TermVectors, because no term mapping across documents in a segment would be
necessary. Though this improvement we can make with a separate jira issue.
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