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From "Andy Isaacson (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-3828) Block Scanner rescans blocks too frequently
Date Thu, 23 Aug 2012 00:13:42 GMT

     [ https://issues.apache.org/jira/browse/HDFS-3828?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Andy Isaacson updated HDFS-3828:
--------------------------------

    Description: 
BlockPoolSliceScanner#scan}} calls cleanUp every time it's invoked from {{DataBlockScanner#run}}
via {{scanBlockPoolSlice}}.  But cleanUp unconditionally {{roll()}}s the verificationLogs,
so after two iterations we have lost the first iteration of block verification times.  As
a result a cluster with just one block repeatedly rescans it every 10 seconds:
{noformat}
2012-08-16 15:59:57,884 INFO  datanode.BlockPoolSliceScanner (BlockPoolSliceScanner.java:verifyBlock(391))
- Verification succeeded for BP-2101131164-172.29.122.91-1337906886255:blk_7919273167187535506_4915
2012-08-16 16:00:07,904 INFO  datanode.BlockPoolSliceScanner (BlockPoolSliceScanner.java:verifyBlock(391))
- Verification succeeded for BP-2101131164-172.29.122.91-1337906886255:blk_7919273167187535506_4915
2012-08-16 16:00:17,925 INFO  datanode.BlockPoolSliceScanner (BlockPoolSliceScanner.java:verifyBlock(391))
- Verification succeeded for BP-2101131164-172.29.122.91-1337906886255:blk_7919273167187535506_4915
{noformat}
{quote}

To fix this, we need to avoid roll()ing the logs multiple times per period.


  was:
Branching off from HDFS-3194:

Andy said:
{quote}
There is still an issue here even with the patch from hdfs-3194-1.txt. Running on a cluster
with just one block we now see
{noformat}
2012-08-16 15:59:57,884 INFO  datanode.BlockPoolSliceScanner (BlockPoolSliceScanner.java:verifyBlock(391))
- Verification succeeded for BP-2101131164-172.29.122.91-1337906886255:blk_7919273167187535506_4915
2012-08-16 16:00:07,904 INFO  datanode.BlockPoolSliceScanner (BlockPoolSliceScanner.java:verifyBlock(391))
- Verification succeeded for BP-2101131164-172.29.122.91-1337906886255:blk_7919273167187535506_4915
2012-08-16 16:00:17,925 INFO  datanode.BlockPoolSliceScanner (BlockPoolSliceScanner.java:verifyBlock(391))
- Verification succeeded for BP-2101131164-172.29.122.91-1337906886255:blk_7919273167187535506_4915
{noformat}
{quote}
Uma said:
bq. Latest patch from Amith should address this issue. 

    
> Block Scanner rescans blocks too frequently
> -------------------------------------------
>
>                 Key: HDFS-3828
>                 URL: https://issues.apache.org/jira/browse/HDFS-3828
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 0.23.0, 2.0.0-alpha
>            Reporter: Andy Isaacson
>            Assignee: Andy Isaacson
>         Attachments: hdfs-3828-1.txt, hdfs3828.txt
>
>
> BlockPoolSliceScanner#scan}} calls cleanUp every time it's invoked from {{DataBlockScanner#run}}
via {{scanBlockPoolSlice}}.  But cleanUp unconditionally {{roll()}}s the verificationLogs,
so after two iterations we have lost the first iteration of block verification times.  As
a result a cluster with just one block repeatedly rescans it every 10 seconds:
> {noformat}
> 2012-08-16 15:59:57,884 INFO  datanode.BlockPoolSliceScanner (BlockPoolSliceScanner.java:verifyBlock(391))
- Verification succeeded for BP-2101131164-172.29.122.91-1337906886255:blk_7919273167187535506_4915
> 2012-08-16 16:00:07,904 INFO  datanode.BlockPoolSliceScanner (BlockPoolSliceScanner.java:verifyBlock(391))
- Verification succeeded for BP-2101131164-172.29.122.91-1337906886255:blk_7919273167187535506_4915
> 2012-08-16 16:00:17,925 INFO  datanode.BlockPoolSliceScanner (BlockPoolSliceScanner.java:verifyBlock(391))
- Verification succeeded for BP-2101131164-172.29.122.91-1337906886255:blk_7919273167187535506_4915
> {noformat}
> {quote}
> To fix this, we need to avoid roll()ing the logs multiple times per period.

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