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https://issues.apache.org/jira/browse/HBASE-810?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12624137#action_12624137
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Jim Kellerman commented on HBASE-810:
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I have attached two screenshots to this issue.
locking-compatibility shows what operations are compatible and how they are
protected from each other
lock-sequencing shows how locking should work. There are a couple of changes
from the current state of affairs:
- StoreFileScanner constructor takes out a read lock on the HStore. This is not
necessary as a read lock is already held in HStore.
- HRegion.get(byte [] row, byte [] column, long timestamp, int numVersions)
(which all the other variants of get call) and HRegion.compactStores() should
take out splitsAndClosesLock.readLock().lock() at the start of the method, and
release it at the end, using try - finally
> 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: Blocker
> Fix For: 0.2.1, 0.3.0
>
> Attachments: lock-sequencing.jpg, locking-compatibility.jpg
>
>
> 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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