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https://issues.apache.org/jira/browse/HBASE-5569?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13233734#comment-13233734
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stack commented on HBASE-5569:
------------------------------
Your 'being extra clear' note needs to become the release note.
What does this mean?
bq. This patch will prevent any deleted KVs from being collected upon flush or
compaction if there is a scanner open with a readpoint smaller than the KV's
memstoreTS (HBASE-2856 does the same for expired KVs).
They stay in memstore or in the snapshot or rather, they are attached to the
outstanding scanners or rather, we still 'see' them in files or memstores if
outstanding scanners and delete is newer than the scanner read point.
Patch looks fine -- makes sense even -- but I'm not up on subtleties that
abound in this code.
We didn't output ts in toString KV? Thats odd.
+1
> Do not collect deleted KVs when they are still in use by a scanner.
> -------------------------------------------------------------------
>
> Key: HBASE-5569
> URL: https://issues.apache.org/jira/browse/HBASE-5569
> Project: HBase
> Issue Type: Bug
> Reporter: Lars Hofhansl
> Assignee: Lars Hofhansl
> Fix For: 0.94.0, 0.96.0
>
> Attachments: 5569-v2.txt, 5569-v3.txt, 5569-v4.txt, 5569.txt,
> TestAtomicOperation-output.trunk_120313.rar
>
>
> I noticed this because TestAtomicOperation.testMultiRowMutationMultiThreads
> fails rarely.
> The solution is similar to HBASE-2856, where expired KVs are not collected
> when in use by a scanner.
> ---
> What I pieced together so far is that it is the *scanning* side that has
> problems sometimes.
> Every time I see a assertion failure in the log I see this before:
> {quote}
> 2012-03-12 21:48:49,523 DEBUG [Thread-211] regionserver.StoreScanner(499):
> Storescanner.peek() is changed where before =
> rowB/colfamily11:qual1/75366/Put/vlen=6,and after =
> rowB/colfamily11:qual1/75203/DeleteColumn/vlen=0
> {quote}
> The order of if the Put and Delete is sometimes reversed.
> The test threads should always see exactly one KV, if the "before" was the
> Put the thread see 0 KVs, if the "before" was the Delete the threads see 2
> KVs.
> This debug message comes from StoreScanner to checkReseek. It seems we still
> some consistency issue with scanning sometimes :(
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