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Subject Poor performance "race condition" in FieldSortedHitQueue
Date Tue, 08 Aug 2006 06:05:36 GMT
Hey all, just want to run an issue that I've recently identified while
looking at some performance issues we are having with our larger
indexes past you all.

Basically what we are seeing is that when there are a number of
concurrent searches being executed over a new IndexSearcher, the quite
expensive ScoreDocComparator generation that is done in the
FieldSortedHitQueue#getCachedComparator method ends up executing
multiple times rather the ideal case of once. This issue does not
effect the correctness of the searches only performance.

For my relatively weak understanding of the code the core of this
issue appears to lie with the FieldCacheImpl#getStringIndex method
which allows multiple concurrent requests to each generate their own
StringIndex rather than allowing the first request to do the
generation and then blocking subsequent requests until the first
request has finished.

Is this a know problem? Should I raise this as an issue or is this
"expected" behaviour. A solution would naturally require more
synchronization than is currently used but nothing particularly



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