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https://issues.apache.org/jira/browse/SOLR-14923?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17226436#comment-17226436
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Mark Robert Miller commented on SOLR-14923:
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I’ll have to look to see. It doesn’t sound like my area at the time, i would
assume Yonik and maybe somehow came through me. If I recall right, I thought
that open is for RTG in general and not just child docs. There are a variety of
other reasons child and atomic docs are slow though. I’ve done a lot on that
path On the ref branch, would be interesting to see how much better it is, but
it doesn’t change the fact that those kind of docs do synchronous instead of
asynchronous updates. Things will also depend how you are sending updates -
streaming, batching, or singles.
> Indexing performance is unacceptable when child documents are involved
> ----------------------------------------------------------------------
>
> Key: SOLR-14923
> URL: https://issues.apache.org/jira/browse/SOLR-14923
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Components: update, UpdateRequestProcessors
> Affects Versions: master (9.0), 8.3, 8.4, 8.5, 8.6
> Reporter: Thomas Wöckinger
> Priority: Critical
> Labels: performance
>
> Parallel indexing does not make sense at moment when child documents are used.
> The org.apache.solr.update.processor.DistributedUpdateProcessor checks at the
> end of the method doVersionAdd if Ulog caches should be refreshed.
> This check will return true if any child document is included in the
> AddUpdateCommand.
> If so ulog.openRealtimeSearcher(); is called, this call is very expensive,
> and executed in a synchronized block of the UpdateLog instance, therefore all
> other operations on the UpdateLog are blocked too.
> Because every important UpdateLog method (add, delete, ...) is done using a
> synchronized block almost each operation is blocked.
> This reduces multi threaded index update to a single thread behavior.
> The described behavior is not depending on any option of the UpdateRequest,
> so it does not make any difference if 'waitFlush', 'waitSearcher' or
> 'softCommit' is true or false.
> The described behavior makes the usage of ChildDocuments useless, because the
> performance is unacceptable.
>
>
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