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Date: Wed, 18 Jun 2014 22:24:24 +0000 (UTC)
From: "churro morales (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
Message-ID: <JIRA.12720469.1402439816539.3936.1403130264924@arcas>
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Subject: [jira] [Commented] (HBASE-11322) SnapshotHFileCleaner makes the
 wrong check for lastModified time thus causing too many cache refreshes
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    [ https://issues.apache.org/jira/browse/HBASE-11322?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14036545#comment-14036545 ] 

churro morales commented on HBASE-11322:
----------------------------------------

No worries, 

If you have 2 different timestamps HBASE-11360 is still a problem.  The cache refresh works but the modified timestamp is still incorrect as it will only get the TS of the time the snapshot was started not the time it completed (I believe)

> SnapshotHFileCleaner makes the wrong check for lastModified time thus causing too many cache refreshes
> ------------------------------------------------------------------------------------------------------
>
>                 Key: HBASE-11322
>                 URL: https://issues.apache.org/jira/browse/HBASE-11322
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 0.94.19
>            Reporter: churro morales
>            Assignee: churro morales
>            Priority: Critical
>             Fix For: 0.94.21
>
>         Attachments: 11322.94.txt, HBASE-11322.patch
>
>
> The SnapshotHFileCleaner calls the SnapshotFileCache if a particular HFile in question is part of a snapshot.
> If the HFile is not in the cache, we then refresh the cache and check again.
> But the cache refresh checks to see if anything has been modified since the last cache refresh but this logic is incorrect in certain scenarios.
> The last modified time is done via this operation:
> {code}
> this.lastModifiedTime = Math.min(dirStatus.getModificationTime(),
>                                      tempStatus.getModificationTime());
> {code}
> and the check to see if the snapshot directories have been modified:
> {code}
> // if the snapshot directory wasn't modified since we last check, we are done
>     if (dirStatus.getModificationTime() <= lastModifiedTime &&
>         tempStatus.getModificationTime() <= lastModifiedTime) {
>       return;
>     }
> {code}
> Suppose the following happens:
> dirStatus modified 6-1-2014
> tempStatus modified 6-2-2014
> lastModifiedTime = 6-1-2014
> provided these two directories don't get modified again all subsequent checks wont exit early, like they should.
> In our cluster, this was a huge performance hit.  The cleaner chain fell behind, thus almost filling up dfs and our namenode heap.
> Its a simple fix, instead of Math.min we use Math.max for the lastModified, I believe that will be correct.
> I'll apply a patch for you guys.


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