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https://issues.apache.org/jira/browse/HDFS-16209?focusedWorklogId=646691&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-646691
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ASF GitHub Bot logged work on HDFS-16209:
-----------------------------------------
Author: ASF GitHub Bot
Created on: 05/Sep/21 11:23
Start Date: 05/Sep/21 11:23
Worklog Time Spent: 10m
Work Description: virajjasani commented on pull request #3378:
URL: https://github.com/apache/hadoop/pull/3378#issuecomment-913134902
Thanks for the reference and find @tomscut !
I agree to the general opinion of not making incompatible change until
absolutely required, and on the other hand, this change looks quite obvious
given that write lock overhead is redundant for non-Cache use-cases. If we want
to use the feature, enable the config, that sounds right.
However, I believe, as of now, we should provide one fat warning log at
appropriate place stating that "please disable this config unless you are using
Cache feature and we are going to disable this config by default in 4.0.0 and
above releases". And we might also want to reference this Jira for perf
degradation case. Thoughts?
Overall, perhaps we might want to wait at least one more major release
before disabling this by default rather than making incompatible change on 3.x
releases.
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Issue Time Tracking
-------------------
Worklog Id: (was: 646691)
Time Spent: 1.5h (was: 1h 20m)
> Set dfs.namenode.caching.enabled to false as default
> ----------------------------------------------------
>
> Key: HDFS-16209
> URL: https://issues.apache.org/jira/browse/HDFS-16209
> Project: Hadoop HDFS
> Issue Type: Improvement
> Affects Versions: 3.1.0
> Reporter: tomscut
> Assignee: tomscut
> Priority: Major
> Labels: pull-request-available
> Time Spent: 1.5h
> Remaining Estimate: 0h
>
> Namenode config:
> dfs.namenode.write-lock-reporting-threshold-ms=50ms
> dfs.namenode.caching.enabled=true (default)
>
> In fact, the caching feature is not used in our cluster, but this switch is
> turned on by default(dfs.namenode.caching.enabled=true), incurring some
> additional write lock overhead. We count the number of write lock warnings in
> a log file, and find that the number of rescan cache warnings reaches about
> 32%, which greatly affects the performance of Namenode.
> !namenode-write-lock.jpg!
>
> We should set 'dfs.namenode.caching.enabled' to false by default and turn it
> on when we wants to use it.
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