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https://issues.apache.org/jira/browse/IMPALA-11409?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Quanlong Huang resolved IMPALA-11409.
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Resolution: Won't Do
Won't do this since after IMPALA-8675, the call on UpdateCatalogMetrics won't
trigger external RPCs so is pretty lightweight now.
> Skip UpdateCatalogMetrics if another thead is on-going in it
> ------------------------------------------------------------
>
> Key: IMPALA-11409
> URL: https://issues.apache.org/jira/browse/IMPALA-11409
> Project: IMPALA
> Issue Type: Improvement
> Components: Backend
> Reporter: Quanlong Huang
> Assignee: Quanlong Huang
> Priority: Critical
> Attachments: jstack-1.txt
>
>
> Impala coordinator tracks local metrics of the catalog, e.g. number of
> dbs/tables. When use_local_catalog is enabled, it also tracks the cache
> metrics, e.g. cache hit/miss count/rate.
> These metrics are updated at the end of each statement, even for simple
> statements like "USE <db>", "SET var=xxx", "SELECT 1". The catalog update
> thread will also update the metrics in the end.
> [https://github.com/apache/impala/blob/bb610dee09a8069bb993b4c668f7e481c1774b70/be/src/service/impala-server.cc#L1272]
> [https://github.com/apache/impala/blob/bb610dee09a8069bb993b4c668f7e481c1774b70/be/src/service/impala-server.cc#L2065]
> These metrics are global metrics of the local catalog cache. They are not
> specifit to a single statement. It's a waste to update the metrics
> concurrently.
> [https://github.com/apache/impala/blob/bb610dee09a8069bb993b4c668f7e481c1774b70/be/src/service/impala-server.cc#L1526-L1559]
> We've seen "hanging issues" that all statements, including the catalog update
> thread, are slowly executing the UpdateCatalogMetrics() function. See details
> in the attached jstack dump.
> Indeed, if one thread is running the UpdateCatalogMetrics() function, the
> other threads can skip it and move forward.
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