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https://issues.apache.org/jira/browse/CASSANDRA-17222?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Benjamin Lerer updated CASSANDRA-17222:
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Change Category: Operability
Complexity: Low Hanging Fruit
Status: Open (was: Triage Needed)
> Add new metrics to track the number of requests performed by GROUP BY and
> Aggregation queries
> ----------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-17222
> URL: https://issues.apache.org/jira/browse/CASSANDRA-17222
> Project: Cassandra
> Issue Type: Improvement
> Components: Observability/Metrics
> Reporter: Benjamin Lerer
> Priority: Normal
>
> When a user perform a GROUP BY query or an aggregate query (e.g. {{SELECT
> count\(\*) FROM my_table}}) internally C* will send multiple internal
> requests to avoid running out of memory. The page size used for those
> internal queries is the same as the external page size.
> Having a some visibility on the number of internal requests happening for a
> group by or an aggregate query is important as it might help administrators
> to debug performance issues.
> We should add some separate metrics for GROUP BY queries and Aggregate queries
> +Additional information for newcomers:+
> * A new metric class called {{AggregationMetrics}} should be created with an
> {{Histogram}} called {{internalPagesPerGroupByQuerie}} and another called
> {{internalPagesPerAggregateQuerie}} (see {{BatchMetrics}} for an example
> * High level query paging are managed by {{AggregationQueryPager}}. The
> number of queries performed should be incremented within {{fetchSubPage}} and
> the metrics should be updated on close.
> * To test that the numbers are reliable, you need to create a new Unit Test
> {{AggregationMetricsTest}}. To have some example of how to test group by
> queries with paging, you can look into
> {{SelectGroupByTest.testGroupByWithPaging()}} to check how to clear the
> histograms between test you can look into
> {{BatchMetricsTests.clearHistogram()}}
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