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https://issues.apache.org/jira/browse/LUCENE-2773?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12935319#action_12935319
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Michael McCandless commented on LUCENE-2773:
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bq. But, lets say you have a 100gb size index, you will end up with 50
segments, no?
So, in the "worst" case, yes... but in the "best" case you could end up with 5
segments. This threshold applies to segments-to-be-merged, so if you have a
bunch of segments just under 2 GB, they will get merged and make a nearly 20 GB
segment, which would then be merged.
So basically this setting is terribly coarse. I think this can be improved (eg
something the lines of BalancedSegmentMergePolicy), perhaps by merging (much)
fewer than mergeFactor segments at a time to keep the immense merges
"smallish". But until we cutover to a better merge policy, we're stuck with
this coarse setting...
So... maybe 5 GB?
But, on the deletes... in 2.9.x and 3.0.x we do NOT in fact take deletions into
account by default; I think, along with this change, we should also fix 2.9.x
and 3.0.x to take deletions into account.
> Don't create compound file for large segments by default
> --------------------------------------------------------
>
> Key: LUCENE-2773
> URL: https://issues.apache.org/jira/browse/LUCENE-2773
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Reporter: Michael McCandless
> Assignee: Michael McCandless
> Fix For: 2.9.4, 3.0.3, 3.1, 4.0
>
> Attachments: LUCENE-2773.patch
>
>
> Spinoff from LUCENE-2762.
> CFS is useful for keeping the open file count down. But, it costs
> some added time during indexing to build, and also ties up temporary
> disk space, causing eg a large spike on the final merge of an
> optimize.
> Since MergePolicy dictates which segments should be CFS, we can
> change it to only build CFS for "smallish" merges.
> I think we should also set a maxMergeMB by default so that very large
> merges aren't done.
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