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Posted to dev@lucene.apache.org by "Iulius Curt (Commented) (JIRA)" <ji...@apache.org> on 2012/03/29 23:15:29 UTC
[jira] [Commented] (LUCENE-2357) Reduce transient RAM usage while
merging by using packed ints array for docID re-mapping
[ https://issues.apache.org/jira/browse/LUCENE-2357?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13241776#comment-13241776 ]
Iulius Curt commented on LUCENE-2357:
-------------------------------------
Could I have some of your time for a few more details, to help a new commer be able to dig into this, please?
> 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
> Priority: Minor
> Labels: gsoc2012, lucene-gsoc-12
> Fix For: 4.0
>
>
> 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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