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From "Jean-Daniel Cryans (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-810) Prevent temporary deadlocks when, during a scan with write operations, the region splits
Date Sat, 09 Aug 2008 01:16:44 GMT
Prevent temporary deadlocks when, during a scan with write operations, the region splits
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                 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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