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https://issues.apache.org/jira/browse/HBASE-15871?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15861055#comment-15861055
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ramkrishna.s.vasudevan commented on HBASE-15871:
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In which branch are you expecting this [~Suh, Sunghan]? Already the patch is in
master and in 1.4 branch?
> Memstore flush doesn't finish because of backwardseek() in memstore scanner.
> ----------------------------------------------------------------------------
>
> Key: HBASE-15871
> URL: https://issues.apache.org/jira/browse/HBASE-15871
> Project: HBase
> Issue Type: Bug
> Components: Scanners
> Affects Versions: 1.1.2
> Reporter: Jeongdae Kim
> Assignee: ramkrishna.s.vasudevan
> Fix For: 2.0.0, 1.4.0
>
> Attachments: HBASE-15871_1.patch, HBASE-15871_1.patch,
> HBASE-15871_2.patch, HBASE-15871_3.patch, HBASE-15871_4.patch,
> HBASE-15871_6.patch, HBASE-15871.branch-1.1.001.patch,
> HBASE-15871.branch-1.1.002.patch, HBASE-15871.branch-1.1.003.patch,
> HBASE-15871-branch-1.patch, HBASE-15871.patch, memstore_backwardSeek().PNG
>
>
> Sometimes in our production hbase cluster, it takes a long time to finish
> memstore flush.( for about more than 30 minutes)
> the reason is that a memstore flusher thread calls
> StoreScanner.updateReaders(), waits for acquiring a lock that store scanner
> holds in StoreScanner.next() and backwardseek() in memstore scanner runs for
> a long time.
> I think that this condition could occur in reverse scan by the following
> process.
> 1) create a reversed store scanner by requesting a reverse scan.
> 2) flush a memstore in the same HStore.
> 3) puts a lot of cells in memstore and memstore is almost full.
> 4) call the reverse scanner.next() and re-create all scanners in this store
> because all scanners was already closed by 2)'s flush() and backwardseek()
> with store's lastTop for all new scanners.
> 5) in this status, memstore is almost full by 2) and all cells in memstore
> have sequenceID greater than this scanner's readPoint because of 2)'s
> flush(). this condition causes searching all cells in memstore, and
> seekToPreviousRow() repeatly seach cells that are already searched if a row
> has one column. (described this in more detail in a attached file.)
> 6) flush a memstore again in the same HStore, and wait until 4-5) process
> finished, to update store files in the same HStore after flusing.
> I searched HBase jira. and found a similar issue. (HBASE-14497) but,
> HBASE-14497's fix can't solve this issue because that fix just changed
> recursive call to loop.(and already applied to our HBase version)
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