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From "Rohini Palaniswamy (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, 21 Jun 2012 18:31:45 GMT

    [ https://issues.apache.org/jira/browse/HIVE-3098?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13398711#comment-13398711
] 

Rohini Palaniswamy commented on HIVE-3098:
------------------------------------------

@Ashutosh,
   We would not hit the wrong token issue mentioned by Daryn, because hive metastore proxies
as the user requesting the operation. The actual ugi with which the operation would be done
is "user via metastoreuser". The metastoreuser UGI is the RealUser and the kerberos TGT of
it is used so there is never a issue of expired or wrong tokens. We have had the same fix
in hdfsproxy and Oozie for 2 years now in production and we have not had issues with it. Hdfsproxy/Oozie
UGI cache is slightly more advanced and they close unused filesystem objects from the cache
after 30 mins or some configured time. Closing the FileSystem object immediately and not taking
advantage of the cache is a bad thing as the fs init operation is costly. Not closing the
filesystem and retaining it in the cache with this fix is not going to cause memory leak unless
you have 10000s of users accessing the hivemetastore. Oozie was doing it for sometime before
the cache expiry logic was added.
                
> 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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