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https://issues.apache.org/jira/browse/LUCENE-845?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12520667
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Michael McCandless commented on LUCENE-845:
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Agreed. OK, I think this is a dead end: it adds complexity and won't
help in "typical" uses of Lucene.
So ... my plan of action is to assess the "actual" O(N^2) cost for
IndexWriter to keep the tail short, add a parameter to LogMergePolicy
so that it "floors" the level and always merges segments less than
this floor together, despite the O(N^2) cost. And then pick a
reasonable default for this floor.
> If you "flush by RAM usage" then IndexWriter may over-merge
> -----------------------------------------------------------
>
> Key: LUCENE-845
> URL: https://issues.apache.org/jira/browse/LUCENE-845
> Project: Lucene - Java
> Issue Type: Bug
> Components: Index
> Affects Versions: 2.1
> Reporter: Michael McCandless
> Assignee: Michael McCandless
> Priority: Minor
> Attachments: LUCENE-845.patch
>
>
> I think a good way to maximize performance of Lucene's indexing for a
> given amount of RAM is to flush (writer.flush()) the added documents
> whenever the RAM usage (writer.ramSizeInBytes()) has crossed the max
> RAM you can afford.
> But, this can confuse the merge policy and cause over-merging, unless
> you set maxBufferedDocs properly.
> This is because the merge policy looks at the current maxBufferedDocs
> to figure out which segments are level 0 (first flushed) or level 1
> (merged from <mergeFactor> level 0 segments).
> I'm not sure how to fix this. Maybe we can look at net size (bytes)
> of a segment and "infer" level from this? Still we would have to be
> resilient to the application suddenly increasing the RAM allowed.
> The good news is to workaround this bug I think you just need to
> ensure that your maxBufferedDocs is less than mergeFactor *
> typical-number-of-docs-flushed.
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