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https://issues.apache.org/jira/browse/LUCENE-7258?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15265590#comment-15265590
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David Smiley commented on LUCENE-7258:
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It appears to me that caching bitsets is a much easier task than most any other
caches I've seen -- there is no key and most (half on average?) bitsets in the
cache will be long enough to be re-used by some subsequent lookup. RE knowing
when an instance can be recycled -- if it were in conjunction with the
QueryCache, then on eviction the bitset can be put into a bitset cache. RE
knowing when bitsets should be evicted, especially for a library -- make that
configurable/disable? _My_ main concern with such a cache is its overall code
impact -- how many places would be touched by it. Perhaps a lot but maybe not
too bad? And of course for what measurable benefit? I imagine some of the GC
cost of the current situation can be addressed with GC tuning -- say raising
the young gen via {{-Xmn}}.
> Tune DocIdSetBuilder allocation rate
> ------------------------------------
>
> Key: LUCENE-7258
> URL: https://issues.apache.org/jira/browse/LUCENE-7258
> Project: Lucene - Core
> Issue Type: Improvement
> Components: modules/spatial
> Reporter: Jeff Wartes
> Attachments:
> LUCENE-7258-Tune-memory-allocation-rate-for-Intersec.patch,
> LUCENE-7258-Tune-memory-allocation-rate-for-Intersec.patch,
> allocation_plot.jpg
>
>
> LUCENE-7211 converted IntersectsPrefixTreeQuery to use DocIdSetBuilder, but
> didn't actually reduce garbage generation for my Solr index.
> Since something like 40% of my garbage (by space) is now attributed to
> DocIdSetBuilder.growBuffer, I charted a few different allocation strategies
> to see if I could tune things more.
> See here: http://i.imgur.com/7sXLAYv.jpg
> The jump-then-flatline at the right would be where DocIdSetBuilder gives up
> and allocates a FixedBitSet for a 100M-doc index. (The 1M-doc index
> curve/cutoff looked similar)
> Perhaps unsurprisingly, the 1/8th growth factor in ArrayUtil.oversize is
> terrible from an allocation standpoint if you're doing a lot of expansions,
> and is especially terrible when used to build a short-lived data structure
> like this one.
> By the time it goes with the FBS, it's allocated around twice as much memory
> for the buffer as it would have needed for just the FBS.
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