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Date: Thu, 13 Jul 2017 22:33:00 +0000 (UTC)
From: "Chen Liang (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.13086724.1499897528000.243712.1499985180077@Atlassian.JIRA>
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Subject: [jira] [Updated] (HDFS-12130) Optimizing permission check for
 getContentSummary
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archived-at: Thu, 13 Jul 2017 22:33:05 -0000


     [ https://issues.apache.org/jira/browse/HDFS-12130?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Chen Liang updated HDFS-12130:
------------------------------
    Attachment: HDFS-12130.003.patch

Post v003 patch. Thanks [~szetszwo] for the review and the offline discussions!!

> 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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