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https://issues.apache.org/jira/browse/HIVE-3098?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13403592#comment-13403592
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Alejandro Abdelnur commented on HIVE-3098:
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Hi Owen, yeah, I do understand we are already hosed on how UGI works and we
cannot change things. Not sure how you suggestion of doAsAndCleanup() would
work as the usecase is a server based system that does not keep state for a
user, not even the UGI but wants to benefit from an ExpirationCache of FS
instances for performance. If the system creates a new UGI for the same user
every time it needs to do something, then there will be a new FS instance every
time and the doAsAndCleanup() will miss all the FS instances created before. In
the case Oozie and HttpFS we need a cache based on the username, we don't
playaround adding/removing credentials to the Subject.
> Memory leak from large number of FileSystem instances in FileSystem.CACHE.
> (Must cache UGIs.)
> ---------------------------------------------------------------------------------------------
>
> Key: HIVE-3098
> URL: https://issues.apache.org/jira/browse/HIVE-3098
> Project: Hive
> Issue Type: Bug
> Components: Shims
> Affects Versions: 0.9.0
> Environment: Running with Hadoop 20.205.0.3+ / 1.0.x with security
> turned on.
> Reporter: Mithun Radhakrishnan
> Assignee: Mithun Radhakrishnan
> Attachments: HIVE-3098.patch
>
>
> The problem manifested from stress-testing HCatalog 0.4.1 (as part of testing
> the Oracle backend).
> The HCatalog server ran out of memory (-Xmx2048m) when pounded by 60-threads,
> in under 24 hours. The heap-dump indicates that hadoop::FileSystem.CACHE had
> 1000000 instances of FileSystem, whose combined retained-mem consumed the
> entire heap.
> It boiled down to hadoop::UserGroupInformation::equals() being implemented
> such that the "Subject" member is compared for equality ("=="), and not
> equivalence (".equals()"). This causes equivalent UGI instances to compare as
> unequal, and causes a new FileSystem instance to be created and cached.
> The UGI.equals() is so implemented, incidentally, as a fix for yet another
> problem (HADOOP-6670); so it is unlikely that that implementation can be
> modified.
> The solution for this is to check for UGI equivalence in HCatalog (i.e. in
> the Hive metastore), using an cache for UGI instances in the shims.
> I have a patch to fix this. I'll upload it shortly. I just ran an overnight
> test to confirm that the memory-leak has been arrested.
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