[
https://issues.apache.org/jira/browse/LUCENE-2357?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13290477#comment-13290477
]
Adrien Grand commented on LUCENE-2357:
--------------------------------------
I ran a quick test that indexes a few millions of documents with only one field
(index, not stored, not analyzed, no terms vectors, ...) with different ratios
of deleted documents, ram buffer sizes (between 1 and 50 MB) and merge factors
(between 3 and 20). The global speedup with {{PackedInts.FAST}} was between
0.2% and 1.7% compared to {{PackedInts.COMPACT}} (although I ran this test on a
low-end computer, other people might have slightly better results with the
{{FAST}} version on a better machine). This is probably not worth the potential
memory overhead. Would someone disagree to replace {{FAST}} with {{COMPACT}}
for the docmaps instantiation?
> 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: Michael McCandless
> Priority: Minor
> Fix For: 4.0
>
> 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.
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators:
https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
