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From "Lars Hofhansl (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5569) Do not collect deleted KVs when they are still in use by a scanner.
Date Sun, 18 Mar 2012 19:38:42 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5569?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13232341#comment-13232341
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Lars Hofhansl commented on HBASE-5569:
--------------------------------------

I spent a lot of more time looking at this. I thought it might be due to the flushes being
executed in parallel by multiple threads, but synchronizing this part made the failure more
likely!
Doing this and increasing the frequency of flushes reproduces the problem multiple times on
every test run now, which it good.

But... My initial hunch was correct. When I enable KEEP_DELETED_CELLS on the store the problem
goes away!
Hence this definitely has to do with collection of deletes and delete markers.
                
> 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.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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