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Posted to hdfs-dev@hadoop.apache.org by "Chen Liang (JIRA)" <ji...@apache.org> on 2017/07/12 22:13:00 UTC
[jira] [Created] (HDFS-12130) Optimizing permission check for
getContentSummary
Chen Liang created HDFS-12130:
---------------------------------
Summary: 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
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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