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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1574) PooledSegmentReader, pools SegmentReader underlying byte arrays
Date Sat, 22 Jan 2011 11:17:44 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1574?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12985091#action_12985091
] 

Michael McCandless commented on LUCENE-1574:
--------------------------------------------

I'm working on an initial patch for this...

bq. I think the only open question is how we'll shrink the pool, most likely there'd be an
expiration on the pooled objects.

I think we can simply have a "max pooled free bit vectors"... or we may want to expire by
time/staleness as well.

bq. With RT, the parallel arrays will grow, so the pool will need to be size based, eg, when
the arrays are grown, all of the previous arrays may be forcefully evicted, or they may simply
expire.

True... but, like the other per-doc arrays, the BV can be overallocated (ArrayUtil.oversize)
to accommodate further added docs.

> PooledSegmentReader, pools SegmentReader underlying byte arrays
> ---------------------------------------------------------------
>
>                 Key: LUCENE-1574
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1574
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: contrib/*
>    Affects Versions: 2.4.1
>            Reporter: Jason Rutherglen
>            Priority: Minor
>             Fix For: 4.0
>
>   Original Estimate: 168h
>  Remaining Estimate: 168h
>
> PooledSegmentReader pools the underlying byte arrays of deleted docs and norms for realtime
search.  It is designed for use with IndexReader.clone which can create many copies of byte
arrays, which are of the same length for a given segment.  When pooled they can be reused
which could save on memory.  
> Do we want to benchmark the memory usage comparison of PooledSegmentReader vs GC?  Many
times GC is enough for these smaller objects.

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