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https://issues.apache.org/jira/browse/HBASE-810?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12621469#action_12621469
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Sebastien Rainville commented on HBASE-810:
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What's the most problematic about this issue is that if we're in the context of
a map/reduce job and that a map task fails when a split occurs then when the
task is restarted it will only scan the rows in the resulting first region...
simply because the input of a hbase map/reduce job is split based on the
regions. Actually, is it a bigger problem that could be the consequence of
other *normal* failures in a map task?
> Prevent temporary deadlocks when, during a scan with write operations, the
> region splits
> ----------------------------------------------------------------------------------------
>
> Key: HBASE-810
> URL: https://issues.apache.org/jira/browse/HBASE-810
> Project: Hadoop HBase
> Issue Type: Bug
> Affects Versions: 0.2.0
> Reporter: Jean-Daniel Cryans
> Priority: Minor
> Fix For: 0.2.1, 0.3.0
>
>
> HBASE-804 was not about the good problem, this one is. Anyone that iterates
> through the results of a scanner and that rewrites data back into the row at
> each iteration will hit a UnknownScannerException if a split occurs. See the
> stack in the referred jira. Timeline :
> Split occurs, acquires a write lock and waits for scanners to finish
> The scanner in the custom code iterates and writes data until the write is
> blocked by the lock
> deadlock
> The scanner timeouts thus the region splits but the USE will be thrown when
> next() is called
> Inside a Map, the task will simply be retried when the first one fails.
> Elsewhere, it becomes more complicated.
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