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Date: Tue, 12 Jun 2012 10:51:44 +0000 (UTC)
From: "Adrien Grand (JIRA)" <jira@apache.org>
To: dev@lucene.apache.org
Message-ID: <1266055936.6927.1339498304051.JavaMail.jiratomcat@issues-vm>
Subject: [jira] [Resolved] (LUCENE-2357) Reduce transient RAM usage while
 merging by using packed ints array for docID re-mapping
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     [ https://issues.apache.org/jira/browse/LUCENE-2357?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Adrien Grand resolved LUCENE-2357.
----------------------------------

    Resolution: Fixed
      Assignee: Adrien Grand  (was: Michael McCandless)
    
> Reduce transient RAM usage while merging by using packed ints array for docID re-mapping
> ----------------------------------------------------------------------------------------
>
>                 Key: LUCENE-2357
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2357
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: core/index
>            Reporter: Michael McCandless
>            Assignee: Adrien Grand
>            Priority: Minor
>             Fix For: 4.0, 5.0
>
>         Attachments: LUCENE-2357.patch, LUCENE-2357.patch, LUCENE-2357.patch, LUCENE-2357.patch, LUCENE-2357.patch
>
>
> We allocate this int[] to remap docIDs due to compaction of deleted ones.
> This uses alot of RAM for large segment merges, and can fail to allocate due to fragmentation on 32 bit JREs.
> Now that we have packed ints, a simple fix would be to use a packed int array... and maybe instead of storing abs docID in the mapping, we could store the number of del docs seen so far (so the remap would do a lookup then a subtract).  This may add some CPU cost to merging but should bring down transient RAM usage quite a bit.

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