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Posted to dev@lucene.apache.org by "Michael McCandless (JIRA)" <ji...@apache.org> on 2012/05/28 16:53:23 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=13284423#comment-13284423 ]
Michael McCandless commented on LUCENE-2357:
--------------------------------------------
Patch looks great!
Do we really need to impl DocMap.equals/hashCode? Costly equals methods scare me... can we simply throw UOE from these methods? Nobody should be calling them, I think.
Instead of looping through numDocs summing up the del count, I think you should be able to set numDeletes = reader.numDeletedDocs()? And maybe just consolidate those two build methods...
> 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
> Fix For: 4.1
>
> Attachments: 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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