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https://issues.apache.org/jira/browse/HDFS-8315?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14529178#comment-14529178
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Gopal V commented on HDFS-8315:
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[~kihwal]: the HDFS in-memory layer is IOPS bound on logging stream - because
log4j uses a single sync block around each appender to maintain ordering of
logs.
I was under the impression that you can always turn on DEBUG logging for a
ClientTraceLog using {{hadoop daemonlog}} command?
> Datanode does not log reads
> ---------------------------
>
> Key: HDFS-8315
> URL: https://issues.apache.org/jira/browse/HDFS-8315
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: Kihwal Lee
> Assignee: Kihwal Lee
> Priority: Critical
> Attachments: HDFS-8315.patch
>
>
> HDFS-6836 made datanode read request logging DEBUG. There is a good reason
> why it was at INFO for so many years. This is very useful in debugging load
> issues. This jira will revert HDFS-6836.
> We haven't seen it being a bottleneck on busy hbase clusters, but if someone
> thinks it is a serious overhead, please make it configurable in a separate
> jira.
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