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https://issues.apache.org/jira/browse/CASSANDRA-19497?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17895769#comment-17895769
]
Caleb Rackliffe commented on CASSANDRA-19497:
---------------------------------------------
Now, if we modify the test above to see what happens on the other extreme, i.e.
global queries over a dataset with single-row partitions...
{noformat}
@Test
public void test() throws Throwable
{
createTable("CREATE TABLE %s (k int, c int, val int, PRIMARY KEY (k, c))");
createIndex("CREATE INDEX ON %s(val) USING 'sai'");
for (int i = 0; i < 10000; i++)
execute("INSERT INTO %s (k, c, val) VALUES (?, ?, ?)", i, 0, i);
flush();
Histogram histogram = new Histogram(4);
for (int i = 0; i < 10000; i++)
{
long start = System.nanoTime();
execute("SELECT k, c FROM %s WHERE val > 9000");
histogram.recordValue(System.nanoTime() - start);
if (i % 1000 == 0)
{
System.err.println("50th: " + histogram.getValueAtPercentile(0.5));
System.err.println("95th: " + histogram.getValueAtPercentile(0.95));
System.err.println("99th: " + histogram.getValueAtPercentile(0.99));
}
}
}
{noformat}
...we get something like this:
|branch|p50 (nanos)|p99 (nanos)|
|trunk|3,030,015|3,064,319|
|patch w/ 100-row batches (that are actually 1-row batches)|2,934,271|2,966,911|
As expected, there's no much difference. (The thread-local might avoid some
{{NavigableSet}} creation in {{makeFilter()}} in the patch.)
> 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: 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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