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https://issues.apache.org/jira/browse/LUCENE-2075?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12781621#action_12781621
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Uwe Schindler commented on LUCENE-2075:
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I changed my benchmark to better show the seek caching effect. For NRQ the
overall improvement has no neglectible effect.
I chenged the rewrite mode of the NRQ to SCORING_BOOLEAN_QUEY and then just
rewrote the queries to BQ and measured time. So no TermDocs/Collecting was in
effect:
trunk: avg number of terms: 68.537; avg seeks=28.838; best time=1.022756 ms;
worst time=17.036802 ms; avg=1.8388833272 ms
patch: avg number of terms: 68.537; avg seeks=28.838; best time=1.066616 ms;
worst time=12.80917 ms; avg=1.6932529156 ms
You see the effect of the caching. The code ran 5000 rewrites with each query
repeated 20 times.
> Share the Term -> TermInfo cache across threads
> -----------------------------------------------
>
> Key: LUCENE-2075
> URL: https://issues.apache.org/jira/browse/LUCENE-2075
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Reporter: Michael McCandless
> Assignee: Michael McCandless
> Priority: Minor
> Fix For: 3.1
>
> Attachments: ConcurrentLRUCache.java, LUCENE-2075.patch,
> LUCENE-2075.patch, LUCENE-2075.patch, LUCENE-2075.patch, LUCENE-2075.patch,
> LUCENE-2075.patch, LUCENE-2075.patch, LUCENE-2075.patch, LUCENE-2075.patch,
> LUCENE-2075.patch
>
>
> Right now each thread creates its own (thread private) SimpleLRUCache,
> holding up to 1024 terms.
> This is rather wasteful, since if there are a high number of threads
> that come through Lucene, you're multiplying the RAM usage. You're
> also cutting way back on likelihood of a cache hit (except the known
> multiple times we lookup a term within-query, which uses one thread).
> In NRT search we open new SegmentReaders (on tiny segments) often
> which each thread must then spend CPU/RAM creating & populating.
> Now that we are on 1.5 we can use java.util.concurrent.*, eg
> ConcurrentHashMap. One simple approach could be a double-barrel LRU
> cache, using 2 maps (primary, secondary). You check the cache by
> first checking primary; if that's a miss, you check secondary and if
> you get a hit you promote it to primary. Once primary is full you
> clear secondary and swap them.
> Or... any other suggested approach?
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