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https://issues.apache.org/jira/browse/PHOENIX-2940?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15310981#comment-15310981
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James Taylor commented on PHOENIX-2940:
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[~ndimiduk] - we don't use stats on the server-side, only the client-side and
FYI, [~maryannxue] comment is related to the calcite branch.
bq. I noticed this conditional {{ if (tenantId == null) {...} }} yesterday and
was rather startled.
We use stats for multi-tenant and non multi-tenant tables alike. We only cache
them on physical tables, because that's how the client uses them. A
multi-tenant table will have the same stats as any other table.
I think the proposal above will solve your issues, Nick and if you have spare
cycles, [~elserj], any effort you could put toward this would be much
appreciated.
We might end up not having space to cache the stats on the client-side either,
in which case we could query for them based on the start/stop row as Maryann
mentioned if we're ok with the extra RPC.
> 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
>
>
> 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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