[jira] [Resolved] (HBASE-11322) SnapshotHFileCleaner makes the wrong check for lastModified time thus causing too many cache refreshes

["Lars Hofhansl (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HBASE-11322?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Lars Hofhansl resolved HBASE-11322.
-----------------------------------

       Resolution: Duplicate
    Fix Version/s:     (was: 0.94.22)
                       (was: 0.98.5)
                       (was: 0.99.0)

Marking as dup of HBASE-11360, which would this issue as well.

> 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
>         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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