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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-2357) Reduce transient RAM usage while merging by using packed ints array for docID re-mapping
Date Mon, 29 Mar 2010 14:03:27 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2357?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12850914#action_12850914
] 

Michael McCandless commented on LUCENE-2357:
--------------------------------------------

I won't have any time to take this any time soon :)  So if anyone has the itch, jump!

> 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: Index
>            Reporter: Michael McCandless
>            Priority: Minor
>             Fix For: 3.1
>
>
> 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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