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From "Daryn Sharp (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-3098) Memory leak from large number of FileSystem instances in FileSystem.CACHE. (Must cache UGIs.)
Date Wed, 27 Jun 2012 20:16:43 GMT

    [ https://issues.apache.org/jira/browse/HIVE-3098?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13402525#comment-13402525
] 

Daryn Sharp commented on HIVE-3098:
-----------------------------------

bq. Or FIX Hadoop FileSystem caching

I wanted to "fix" the cache for the NM, but after digging around, I think the cache is working
as designed.  UGIs are mutable, so if two different requests share the same cached UGI, then
tokens from one request will be shared with another request.  This contamination may lead
to security issues and will cause bugs.
                
> 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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