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https://issues.apache.org/jira/browse/COUCHDB-2984?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15277084#comment-15277084
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ASF subversion and git services commented on COUCHDB-2984:
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Commit 0b70afb7cc11f39e894a37211349e4444711facb in couchdb-mem3's branch
refs/heads/master from [~banjiewen]
[ https://git-wip-us.apache.org/repos/asf?p=couchdb-mem3.git;h=0b70afb ]
Add read_concurrency option to mem3_shards table
This table sees a great deal of activity from various subsystems -
turning on read_concurrency should be a win.
COUCHDB-2984
> mem3_sync event listener performance degrades with high q values
> ----------------------------------------------------------------
>
> Key: COUCHDB-2984
> URL: https://issues.apache.org/jira/browse/COUCHDB-2984
> Project: CouchDB
> Issue Type: Improvement
> Reporter: Benjamin Anderson
>
> High throughput applications on databases with high (300+) q values have a
> tendency to cause very poor performance. While I don't fully understand the
> issue at hand, one clear manifestation is in mem3_sync's event listener. With
> high q values, the shard "selection" routine (the <<"shards/",ยท_/binary>>
> head of handle_event/3) will bottleneck on calls to mem3_shards:for_db/1 due
> to the large (tens of KB) shard maps in ETS.
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