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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-7868) Use multiple threads to apply deletes and DV updates
Date Fri, 16 Jun 2017 13:24:00 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-7868?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16051880#comment-16051880
] 

Michael McCandless commented on LUCENE-7868:
--------------------------------------------

I posted the last patch in Review Board: https://reviews.apache.org/r/60154/

> 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
>
>
> 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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