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https://issues.apache.org/jira/browse/CASSANDRA-14466?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16502584#comment-16502584
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Mulugeta Mammo commented on CASSANDRA-14466:
--------------------------------------------
The results we posted are based on a read_ahead_kb value of 8, a chunk size of
64KB and a uniform distribution invocation:
{{cassandra-stress user
profile=$CASSANDRA_TOOLS/cqlstress-insanity-example.yaml ops\(simple1=1\)
no-warmup cl=ONE duration=300s -mode native cql3 -pop
dist=uniform\(1..1200000000\) -node server_ip -rate threads=288}}
And no we don’t see any significant difference if we set the read_ahead_kb to
0. For a buffered run with read_ahead_kb set to 0 vs 8, we observed just a 5%
increase in throughput for the 0.
Also, for all of our runs, the Cassandra caches (row cache, key cache, etc.)
were disabled. For a cacheable data, we believe a better solution is to have
the caches enabled and tuned instead of relying on the page cache. Generally,
we believe relying on the page cache is not a good strategy as the application
has no control over the caching. The problem also gets worse if other
applications, e.g. a Spark analytics workload, are running on the same node.
You may download and test it, git clone -b direct_io
[https://github.com/mulugetam/cassandra.git] (requires JDK 10)
> Enable Direct I/O
> ------------------
>
> Key: CASSANDRA-14466
> URL: https://issues.apache.org/jira/browse/CASSANDRA-14466
> Project: Cassandra
> Issue Type: New Feature
> Components: Local Write-Read Paths
> Reporter: Mulugeta Mammo
> Priority: Major
> Attachments: direct_io.patch
>
>
> Hi,
> JDK 10 introduced a new API for Direct IO that enables applications to bypass
> the file system cache and potentially improve performance. Details of this
> feature can be found at [https://bugs.openjdk.java.net/browse/JDK-8164900].
> This patch uses the JDK 10 API to enable Direct IO for the Cassandra read
> path. By default, we have disabled this feature; but it can be enabled using
> a new configuration parameter, enable_direct_io_for_read_path. We have
> conducted a Cassandra read-only stress test and measured a throughput gain of
> up to 60% on flash drives.
> The patch requires JDK 10 Cassandra Support -
> https://issues.apache.org/jira/browse/CASSANDRA-9608
> Please review the patch and let us know your feedback.
> Thanks,
> [^direct_io.patch]
>
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