[jira] [Commented] (CASSANDRA-19497) ResultRetriever should batch clusterings/rows during SAI post-filtering reads

["Caleb Rackliffe (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-19497?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17894922#comment-17894922 ] 

Caleb Rackliffe commented on CASSANDRA-19497:
---------------------------------------------

Attached two more flamegraphs to document the overhead of all the non-batched single-partition reads: [^cpu-trunk.html] [^alloc-trunk.html]

> ResultRetriever should batch clusterings/rows during SAI post-filtering reads
> -----------------------------------------------------------------------------
>
>                 Key: CASSANDRA-19497
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-19497
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Feature/SAI
>            Reporter: Caleb Rackliffe
>            Assignee: Caleb Rackliffe
>            Priority: Normal
>             Fix For: 5.0.x, 5.x
>
>         Attachments: alloc-trunk.html, cpu-trunk.html, heap-flamegraph.html, wall-no-parked-threads.html
>
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> SAI currently creates and executes a {{SinglePartitionReadCommand}} for every {{PrimaryKey}} the index produces to read the corresponding row for post-filtering. Informed by the limits present in the read command itself, it should be possible to batch those reads w/ a {{ClusteringIndexNamesFilter}} in many fewer {{SinglePartitionReadCommands}}. When we have a handful of matches in a large partition, this seems like would involve many fewer seeks, less unnecessary object creation, etc.



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