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Date: Tue, 18 Sep 2012 04:59:08 +1100 (NCT)
From: "Tim Smith (JIRA)" <jira@apache.org>
To: dev@lucene.apache.org
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Subject: [jira] [Commented] (LUCENE-4398) "Memory Leak" in TermsHashPerField
 memory tracking
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    [ https://issues.apache.org/jira/browse/LUCENE-4398?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13457196#comment-13457196 ] 

Tim Smith commented on LUCENE-4398:
-----------------------------------

Looks like the culprit is DocFieldProcessorPerThread.trimFields()

this method "releases" fields that were not seen recently
for each field, this leaks 16 bytes from DocumentsWriter.bytesUsed's memory accounting
                
> "Memory Leak" in TermsHashPerField memory tracking
> --------------------------------------------------
>
>                 Key: LUCENE-4398
>                 URL: https://issues.apache.org/jira/browse/LUCENE-4398
>             Project: Lucene - Core
>          Issue Type: Bug
>    Affects Versions: 3.4
>            Reporter: Tim Smith
>
> I am witnessing an apparent leak in the memory tracking used to determine when a flush is necessary.
> Over time, this will result in every single document being flushed into its own segment as the memUsage will remain above the configured buffer size, causing a flush to be triggered after every add/update.
> Best I can figure, this is being caused by TermsHashPerField's tracking of memory usage for postingsHash and/or postingsArray combined with multi-threaded feeding.
> I suspect that the TermsHashPerField's postingsHash is growing in one thread, then, when a segment is flushed, a single, different thread will merge all TermsHashPerFields in FreqProxTermsWriter and then call shrinkHash(). I suspect this call of shrinkHash() is seeing an old postingsHash array, and subsequently not releasing all the memory that was allocated.
> If this is the case, I am also concerned that FreqProxTermsWriter will not write the correct terms into the index, although I have not confirmed that any indexing problem occurs as of yet.
> NOTE: i am witnessing this growth in a test by subtracting the amount or memory allocated (but in a "free" state) by perDocAllocator/byteBlockAllocator/charBlocks/intBlocks from DocumentsWriter.memUsage.get() in IndexWriter.doAfterFlush()
> I will see this stay at a stable point for a while, then on some flushes, i will see this grow by a couple of bytes, and all subsequent flushes will never go back down the the previous state
> I will continue to investigate and post any additional findings

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