[jira] [Commented] (LUCENE-7868) Use multiple threads to apply deletes and DV updates

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[jira] [Commented] (LUCENE-7868) Use multiple threads to apply deletes and DV updates

JIRA jira@apache.org

    [ https://issues.apache.org/jira/browse/LUCENE-7868?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16053746#comment-16053746 ]

Simon Willnauer commented on LUCENE-7868:
-----------------------------------------

[~mikemccand] I did a second pass.. I think we are close

> Use multiple threads to apply deletes and DV updates
> ----------------------------------------------------
>
>                 Key: LUCENE-7868
>                 URL: https://issues.apache.org/jira/browse/LUCENE-7868
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>             Fix For: master (7.0)
>
>         Attachments: cpu-after.png, cpu-before.png, LUCENE-7868.patch, LUCENE-7868.patch, LUCENE-7868.patch, LUCENE-7868.patch, LUCENE-7868.patch
>
>
> Today, when users delete documents or apply doc values updates, IndexWriter buffers them up into frozen packets and then eventually uses a single thread (BufferedUpdatesStream.applyDeletesAndUpdates) to resolve delete/update terms to docids.  This thread also holds IW's monitor lock, so it also blocks refresh, merges starting/finishing, commits, etc.
> We have heavily optimized this part of Lucene over time, e.g. LUCENE-6161, LUCENE-2897, LUCENE-2680, LUCENE-3342, but still, it's a single thread so it can't use multiple CPU cores commonly available now.
> This doesn't affect append-only usage, but for update-heavy users (me!) this can be a big bottleneck, and causes long stop-the-world hangs during indexing.
> I have an initial exploratory patch to make these lookups concurrent, without holding IW's lock, so that when a new packet of deletes is pushed, which happens when we flush a new segment, we immediately use that same indexing thread to and resolve the deletions.
> This is analogous to when we made segment flushing concurrent (LUCENE-3023), just for deletes and DV updates as well.



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