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From "Robert Muir (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-6383) MemoryPostings fst encoding can be surprisingly inefficient (especially in tests, with payloads)
Date Wed, 01 Apr 2015 04:38:53 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-6383?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14389982#comment-14389982
] 

Robert Muir commented on LUCENE-6383:
-------------------------------------

We should also look into why [~jpountz]'s test for "things getting bigger on merge" (BaseIndexFileFormatTestCase.testMergeStability)
doesnt find this. 

Maybe the problems are specific to payloads? BasePostingsFormat.addRandomFields iterates through
all the possible index options, but never adds any payloads. Could be a tricky thing to do
in tests in general, because of optimizations when payloads have the same length.

There is a TODO in TestMemoryPostingsFormat to randomize pack=true/false. Maybe its related
too, TestMemoryPF never tests that, but RandomCodec randomizes the option.


> MemoryPostings fst encoding can be surprisingly inefficient (especially in tests, with
payloads)
> ------------------------------------------------------------------------------------------------
>
>                 Key: LUCENE-6383
>                 URL: https://issues.apache.org/jira/browse/LUCENE-6383
>             Project: Lucene - Core
>          Issue Type: Bug
>            Reporter: Robert Muir
>
> I just worked around this in 2 nightly OOM fails.
> One was TestDuelingCodecs, the other was TestIndexWriterForceMerge's space usage test.
> In general the trend is the same, it seems the more documents you merge, you just get
bigger and bigger FST outputs and the size of this PF in ram and on disk grows in a way you
don't expect. E.g. merging 300KB of segments resulted in 450KB single segment, and memory
usage gets absurdly high.
> The issue seems especially aggravated in tests, when MockAnalyzer adds lots of payloads.
> Maybe it should encode the postings data in a more efficient way? Can it just use a Long
output pointing into a RAMFile or something? Or maybe there is just a crazy bug?



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