[jira] [Commented] (CASSANDRA-17222) Add new metrics to track the number of requests performed by GROUP BY and Aggregation queries

["Venkata Harikrishna Nukala (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-17222?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17480661#comment-17480661 ] 

Venkata Harikrishna Nukala commented on CASSANDRA-17222:
--------------------------------------------------------

Can I pick it?

> 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
>              Labels: AdventCalendar2021, lhf
>             Fix For: 4.x
>
>
> 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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