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https://issues.apache.org/jira/browse/CASSANDRA-19497?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17896093#comment-17896093
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Caleb Rackliffe commented on CASSANDRA-19497:
---------------------------------------------
Alright, so I went back and created a thing I'm calling
{{InsertionOrderedNavigableSet}}. It's a very limited implementation of
{{NavigableSet}} that assumes elements are added in-order and explodes if they
aren't. This means insertion is constant time, and we avoid the {{TreeSet}}
building overhead from the first cut of the patch. Did a final run of my little
test:
|branch|p50 (nanos)|p99 (nanos)|
|trunk|9,031,679|9,058,303|
|patch w/ TreeSet|1,302,847|1,320,255|
|patch w/ InsertionOrderedNavigableSet |955,423|971,231|
So we're approaching a 10x improvement in latency for the CPU-bound part of a
partition-restricted query with 1000 results on a partition of 10,000 rows.
> 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-batch-100-19497.png,
> cpu-trunk-19497.png, cpu-trunk.html, heap-flamegraph.html,
> wall-no-parked-threads.html
>
> Time Spent: 50m
> 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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