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https://issues.apache.org/jira/browse/HADOOP-19847?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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yue.wang updated HADOOP-19847:
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Attachment: logAllocatedBlock takes lots of time.png
Description:
The {{logAllocatedBlock}} method in {{FSNamesystem.getAdditionalBlock}} is
currently called while holding {{{}fsLock{}}}. Flame graph analysis shows this
logging path (via SLF4J/Log4j appenders) contributes non-trivial latency,
blocking other NameNode operations.
Since {{logAllocatedBlock}} is only for audit/diagnostic logging and does not
modify shared state, we can safely move it after releasing {{fsLock}} to reduce
lock hold time and improve write throughput.
This change preserves all existing logging behavior while eliminating
unnecessary lock contention from I/O-bound logging operations.
Flame graph:
!logAllocatedBlock takes lots of time.png|width=1083,height=378!
> Move logAllocatedBlock out of lock in FSNamesystem.getAdditionalBlock to
> reduce latency
> ---------------------------------------------------------------------------------------
>
> Key: HADOOP-19847
> URL: https://issues.apache.org/jira/browse/HADOOP-19847
> Project: Hadoop Common
> Issue Type: Improvement
> Components: hdfs
> Affects Versions: 3.3.6
> Reporter: yue.wang
> Priority: Major
> Labels: HDFS
> Attachments: logAllocatedBlock takes lots of time.png
>
>
> The {{logAllocatedBlock}} method in {{FSNamesystem.getAdditionalBlock}} is
> currently called while holding {{{}fsLock{}}}. Flame graph analysis shows
> this logging path (via SLF4J/Log4j appenders) contributes non-trivial
> latency, blocking other NameNode operations.
>
> Since {{logAllocatedBlock}} is only for audit/diagnostic logging and does not
> modify shared state, we can safely move it after releasing {{fsLock}} to
> reduce lock hold time and improve write throughput.
>
> This change preserves all existing logging behavior while eliminating
> unnecessary lock contention from I/O-bound logging operations.
>
> Flame graph:
> !logAllocatedBlock takes lots of time.png|width=1083,height=378!
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