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