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From "Jitendra Nath Pandey (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-3098) Memory leak from large number of FileSystem instances in FileSystem.CACHE. (Must cache UGIs.)
Date Thu, 28 Jun 2012 17:50:44 GMT

    [ https://issues.apache.org/jira/browse/HIVE-3098?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13403290#comment-13403290
] 

Jitendra Nath Pandey commented on HIVE-3098:
--------------------------------------------

bq. Problem stems from the fact that there is no expiration policy either in fs or ugi cache.
We need to design for UGI cache eviction policy. There, when we are expiring stale ugi's from
ugi-cache we can do closeAllForUGI for evicting ugi to evict cached FS objects from fs-cache.

+1. It may be more tractable to have a cache expiration policy in ugi-cache based on the semantics
of this particular use case. In FS-cache it gets trickier because of the general purpose nature
of the file system.
                
> 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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