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https://issues.apache.org/jira/browse/HBASE-16721?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15530523#comment-15530523
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Enis Soztutar commented on HBASE-16721:
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bq. It turned out that the two regions were opened and hosted on other region
servers, not on this region server.
Do you know that whether these regions were opened before on this host, then
closed. If it is, it maybe the same issue. At the time of the log roller and
log file cleanup, the region to force flush is already closed some time ago,
but WAL still thinks that there is unflushed entries from this region.
> Concurrency issue in WAL unflushed seqId tracking
> -------------------------------------------------
>
> Key: HBASE-16721
> URL: https://issues.apache.org/jira/browse/HBASE-16721
> Project: HBase
> Issue Type: Bug
> Reporter: Enis Soztutar
> Assignee: Enis Soztutar
> Fix For: 2.0.0, 1.3.0, 1.4.0, 1.1.7, 1.2.4
>
>
> I'm inspecting an interesting case where in a production cluster, some
> regionservers ends up accumulating hundreds of WAL files, even with force
> flushes going on due to max logs. This happened multiple times on the
> cluster, but not on other clusters. The cluster has periodic memstore flusher
> disabled, however, this still does not explain why the force flush of regions
> due to max limit is not working. I think the periodic memstore flusher just
> masks the underlying problem, which is why we do not see this in other
> clusters.
> The problem starts like this:
> {code}
> 2016-09-21 17:49:18,272 INFO [regionserver//10.2.0.55:16020.logRoller]
> wal.FSHLog: Too many wals: logs=33, maxlogs=32; forcing flush of 1
> regions(s): d4cf39dc40ea79f5da4d0cf66d03cb1f
> 2016-09-21 17:49:18,273 WARN [regionserver//10.2.0.55:16020.logRoller]
> regionserver.LogRoller: Failed to schedule flush of
> d4cf39dc40ea79f5da4d0cf66d03cb1f, region=null, requester=null
> {code}
> then, it continues until the RS is restarted:
> {code}
> 2016-09-23 17:43:49,356 INFO [regionserver//10.2.0.55:16020.logRoller]
> wal.FSHLog: Too many wals: logs=721, maxlogs=32; forcing flush of 1
> regions(s): d4cf39dc40ea79f5da4d0cf66d03cb1f
> 2016-09-23 17:43:49,357 WARN [regionserver//10.2.0.55:16020.logRoller]
> regionserver.LogRoller: Failed to schedule flush of
> d4cf39dc40ea79f5da4d0cf66d03cb1f, region=null, requester=null
> {code}
> The problem is that region {{d4cf39dc40ea79f5da4d0cf66d03cb1f}} is already
> split some time ago, and was able to flush its data and split without any
> problems. However, the FSHLog still thinks that there is some unflushed data
> for this region.
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