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https://issues.apache.org/jira/browse/PHOENIX-2940?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15330197#comment-15330197
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Josh Elser commented on PHOENIX-2940:
-------------------------------------
Figures, once I step back, I figure it out.
There is a difference in the assertion of priority for the priority. When the
client is doing the stats lookup, it's setting the priority based on
PayloadCarryingRpcController. When this call happens in the server, it must be
reaching out to the PhoenixRpcScheduler somehow.
> Remove STATS RPCs from rowlock
> ------------------------------
>
> Key: PHOENIX-2940
> URL: https://issues.apache.org/jira/browse/PHOENIX-2940
> Project: Phoenix
> Issue Type: Improvement
> Environment: HDP 2.3 + Apache Phoenix 4.6.0
> Reporter: Nick Dimiduk
> Assignee: Josh Elser
> Fix For: 4.9.0
>
> Attachments: PHOENIX-2940.001.patch, PHOENIX-2940.002.patch
>
>
> We have an unfortunate situation wherein we potentially execute many RPCs
> while holding a row lock. This is problem is discussed in detail on the user
> list thread ["Write path blocked by MetaDataEndpoint acquiring region
> lock"|http://search-hadoop.com/m/9UY0h2qRaBt6Tnaz1&subj=Write+path+blocked+by+MetaDataEndpoint+acquiring+region+lock].
> During some situations, the
> [MetaDataEndpoint|https://github.com/apache/phoenix/blob/10909ae502095bac775d98e6d92288c5cad9b9a6/phoenix-core/src/main/java/org/apache/phoenix/coprocessor/MetaDataEndpointImpl.java#L492]
> coprocessor will attempt to refresh it's view of the schema definitions and
> statistics. This involves [taking a
> rowlock|https://github.com/apache/phoenix/blob/10909ae502095bac775d98e6d92288c5cad9b9a6/phoenix-core/src/main/java/org/apache/phoenix/coprocessor/MetaDataEndpointImpl.java#L2862],
> executing a scan against the [local
> region|https://github.com/apache/phoenix/blob/10909ae502095bac775d98e6d92288c5cad9b9a6/phoenix-core/src/main/java/org/apache/phoenix/coprocessor/MetaDataEndpointImpl.java#L542],
> and then a scan against a [potentially
> remote|https://github.com/apache/phoenix/blob/10909ae502095bac775d98e6d92288c5cad9b9a6/phoenix-core/src/main/java/org/apache/phoenix/coprocessor/MetaDataEndpointImpl.java#L964]
> statistics table.
> This issue is apparently exacerbated by the use of user-provided timestamps
> (in my case, the use of the ROW_TIMESTAMP feature, or perhaps as in
> PHOENIX-2607). When combined with other issues (PHOENIX-2939), we end up with
> total gridlock in our handler threads -- everyone queued behind the rowlock,
> scanning and rescanning SYSTEM.STATS. Because this happens in the
> MetaDataEndpoint, the means by which all clients refresh their knowledge of
> schema, gridlock in that RS can effectively stop all forward progress on the
> cluster.
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