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https://issues.apache.org/jira/browse/HBASE-24779?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17165815#comment-17165815
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Josh Elser commented on HBASE-24779:
------------------------------------
{noformat}
"regionserver/my-regionserver:16020.replicationSource.my-regionserver.domain.com%2C16020%2C1595762757628,<peerId>.replicationSource.wal-reader.my-regionserver.domain.com%2C16020%2C1595762757628,<peerId>"
#531 daemon prio=5 os_prio=0 tid=0x00007f0680d21000 nid=0x2c0eb
sleeping[0x00007ef3bf827000]
java.lang.Thread.State: TIMED_WAITING (sleeping)
at java.lang.Thread.sleep(Native Method)
at org.apache.hadoop.hbase.util.Threads.sleep(Threads.java:148)
at
org.apache.hadoop.hbase.replication.regionserver.ReplicationSourceWALReader.checkQuota(ReplicationSourceWALReader.java:227)
at
org.apache.hadoop.hbase.replication.regionserver.ReplicationSourceWALReader.run(ReplicationSourceWALReader.java:130)
Locked ownable synchronizers:
- None
{noformat}
For example, this is one of the {{wal-reader}} threads which is "hung" in a
loop, never actually reading entries off of the WALs. You may see one to many
of these (many, if this RS is also reading recovered queues in addition to its
active WAL)
> Improve insight into replication WAL readers hung on checkQuota
> ---------------------------------------------------------------
>
> Key: HBASE-24779
> URL: https://issues.apache.org/jira/browse/HBASE-24779
> Project: HBase
> Issue Type: Task
> Reporter: Josh Elser
> Assignee: Josh Elser
> Priority: Minor
>
> Helped a customer this past weekend who, with a large number of
> RegionServers, has some RegionServers which replicated data to a peer without
> issues while other RegionServers did not.
> The number of queue logs varied over the past 24hrs in the same manner. Some
> spikes in queued logs into 100's of logs, but other times, only 1's-10's of
> logs were queued.
> We were able to validate that there were "good" and "bad" RegionServers by
> creating a test table, assigning it to a regionserver, enabling replication
> on that table, and validating if the local puts were replicated to a peer. On
> a good RS, data was replicated immediately. On a bad RS, data was never
> replicated (at least, on the order of 10's of minutes which we waited).
> On the "bad RS", we were able to observe that the \{{wal-reader}} thread(s)
> on that RS were spending time in a Thread.sleep() in a different location
> than the other. Specifically it was sitting in the
> {{ReplicationSourceWALReader#checkQuota()}}'s sleep call, _not_ the
> {{handleEmptyWALBatch()}} method on the same class.
> My only assumption is that, somehow, these RegionServers got into a situation
> where they "allocated" memory from the quota but never freed it. Then,
> because the WAL reader thinks it has no free memory, it blocks indefinitely
> and there are no pending edits to ship and (thus) free that memory. A cursory
> glance at the code gives me a _lot_ of anxiety around places where we don't
> properly clean it up (e.g. batches that fail to ship, dropping a peer). As a
> first stab, let me add some more debugging so we can actually track this
> state properly for the operators and their sanity.
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