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https://issues.apache.org/jira/browse/LUCENE-2075?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12782035#action_12782035
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Michael McCandless commented on LUCENE-2075:
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{quote}
bq. I am quite sure that also Robert's test is random (as he explained).
It's not random - it's the specified pattern, parsed to
WildcardQuery, run 10 times, then take best or avg time.
{quote}
Woops -- I was wrong here -- Robert's test is random: on each iteration, it
replaces any N's in the pattern w/ a random number 0-9.
Still baffled on why the linear scan shows gains w/ the cache... digging.
> 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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