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From "Jeongdae Kim (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-15871) Memstore flush doesn't finish because of backwardseek() in memstore scanner.
Date Wed, 01 Jun 2016 08:03:59 GMT

    [ https://issues.apache.org/jira/browse/HBASE-15871?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15309894#comment-15309894

Jeongdae Kim commented on HBASE-15871:

No, not applied yet.
I tested several times with this patch, and the issue didn't reproduce.

> 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
>             Fix For: 1.1.2
>         Attachments: HBASE-15871.branch-1.1.001.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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