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Chen Liang commented on HDFS-12130:
-----------------------------------
The failed tests are unrelated and all passed in my local run. The checkstyle warning is due
to the existing style issue in {{BlockCollection}} that actually all the {{public}} modifier
are redundant, will file a separate jira to fix it. The findbug warnings are also unrelated.
> Optimizing permission check for getContentSummary
> -------------------------------------------------
>
> Key: HDFS-12130
> URL: https://issues.apache.org/jira/browse/HDFS-12130
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode
> Reporter: Chen Liang
> Assignee: Chen Liang
> Attachments: HDFS-12130.001.patch, HDFS-12130.002.patch
>
>
> Currently, {{getContentSummary}} takes two phases to complete:
> - phase1. check the permission of the entire subtree. If any subdirectory does not have
{{READ_EXECUTE}}, an access control exception is thrown and {{getContentSummary}} terminates
here (unless it's super user).
> - phase2. If phase1 passed, it will then traverse the entire tree recursively to get
the actual content summary.
> An issue is, both phases currently hold the fs lock.
> Phase 2 has already been written that, it will yield the fs lock over time, such that
it does not block other operations for too long. However phase 1 does not yield. Meaning it's
possible that the permission check phase still blocks things for long time.
> One fix is to add lock yield to phase 1. But a simpler fix is to merge phase 1 into phase
2. Namely, instead of doing a full traversal for permission check first, we start with phase
2 directly, but for each directory, before obtaining its summary, check its permission first.
This way we take advantage of existing lock yield in phase 2 code and still able to check
permission and terminate on access exception.
> Thanks [~szetszwo] for the offline discussions!
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