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https://issues.apache.org/jira/browse/HDFS-12130?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16087652#comment-16087652
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Chen Liang commented on HDFS-12130:
-----------------------------------
Thanks [~szetszwo] for the review! The failed tests are unrelated, and passed
locally.
> 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,
> HDFS-12130.003.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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