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https://issues.apache.org/jira/browse/CASSANDRA-16436?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17467696#comment-17467696
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Paulo Motta commented on CASSANDRA-16436:
-----------------------------------------
Thanks. I added some minor follow-up review changes on [this
PR|https://github.com/subkanthi/cassandra/pull/1/files] to your branch. Let me
know what do you think.
I tested the patch locally on a docker image and got the expected message when
there is a high read_ahead_kb setting:
{noformat}
WARN [main] 2022-01-02 19:54:25,030 StartupChecks.java:358 - Detected high
'/sys/block/vda/queue/read_ahead_kb' setting of 4096 for device '/dev/vda1' of
data directory '/opt/cassandra/data/data'. It is recommended to set this value
to 8(KB) on SSDs or 64(KB) on HDDs to prevent excessive IO usage and page cache
churn on read-intensive workloads.
{noformat}
I checked the warning is not print when the read_ahead_kb setting is below
128KB.
Final patch and CI:
|[trunk|https://github.com/apache/cassandra/compare/trunk...pauloricardomg:subkanthi/16436-trunk-rebased]|[tests|https://ci-cassandra.apache.org/view/patches/job/Cassandra-devbranch/1342/]|
> Add startup check for large read_ahead_kb setting
> -------------------------------------------------
>
> Key: CASSANDRA-16436
> URL: https://issues.apache.org/jira/browse/CASSANDRA-16436
> Project: Cassandra
> Issue Type: Improvement
> Components: Local/Startup and Shutdown
> Reporter: Paulo Motta
> Assignee: Kanthi Subramanian
> Priority: Normal
> Labels: AdventCalendar2021, lhf
>
> A well known production tuning recommendation is to dial back the
> {{read_ahead_kb}} Linux setting from the default of 4096 in most
> distributions as this can cause high IO usage and cache churn on
> read-intensive workloads.
> We should add a startup warning to detect when a high {{read_ahead_kb}} is
> used and recommend the user to dial back to a reasonable value, which varies
> according to the workload but a general guideline is to tune this to 8kb.
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