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From "Ted Yu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-18099) FlushSnapshotSubprocedure should check the return value from Region#flush()
Date Wed, 24 May 2017 23:43:04 GMT

    [ https://issues.apache.org/jira/browse/HBASE-18099?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16023894#comment-16023894
] 

Ted Yu commented on HBASE-18099:
--------------------------------

bq. Either there is nothing to flush
If there is nothing to flush, FlushResult.Result.CANNOT_FLUSH wouldn't have been returned
- CANNOT_FLUSH_MEMSTORE_EMPTY would be returned.

This check acts as safety guard. Normally waitForFlushes() would get into loop and return
non-zero value.

> FlushSnapshotSubprocedure should check the return value from Region#flush()
> ---------------------------------------------------------------------------
>
>                 Key: HBASE-18099
>                 URL: https://issues.apache.org/jira/browse/HBASE-18099
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Ted Yu
>         Attachments: 18099.v1.txt, 18099.v2.txt
>
>
> In the following thread:
> http://search-hadoop.com/m/HBase/YGbbMXkeHlI9zo
> Jacob described the scenario where data from certain region were missing in the snapshot.
> Here was related region server log:
> https://pastebin.com/1ECXjhRp
> He pointed out that concurrent flush from MemStoreFlusher.1 thread was not initiated
from the thread pool for snapshot.
> In RegionSnapshotTask#call() method there is this:
> {code}
>           region.flush(true);
> {code}
> The return value is not checked.
> In HRegion#flushcache(), Result.CANNOT_FLUSH may be returned due to:
> {code}
>           String msg = "Not flushing since "
>               + (writestate.flushing ? "already flushing"
>               : "writes not enabled");
> {code}
> This implies that FlushSnapshotSubprocedure may incorrectly skip waiting for the concurrent
flush to complete.



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