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https://issues.apache.org/jira/browse/HBASE-2952?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12905171#action_12905171
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Jonathan Gray commented on HBASE-2952:
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One issue with relying on HTables to be closed is that this would introduce a
kind of incompatible API change. Previously, we have not required (or
encouraged) users to close() their HTables unless they are using the write
buffer. Those using HTablePool never really call HTable.close().
Could we add something into HCM that would allow you to attach shutdown
handlers to HCM that would be called before running its own logic? Like
HCM.registerShutdownHook(Thread) or whatever the interface is.
> HConnectionManager's shutdown hook interferes with client's operations
> ----------------------------------------------------------------------
>
> Key: HBASE-2952
> URL: https://issues.apache.org/jira/browse/HBASE-2952
> Project: HBase
> Issue Type: Improvement
> Components: client
> Affects Versions: 0.20.0
> Reporter: Prakash Khemani
>
> My HBase client calls incrementColValue() in pairs. If someone kills the
> client (SIGINT or SIGTERM) I want my client's increment threads to gracefully
> exit. If a thread has already done one of the incrementColValue() then I want
> that thread to complete the other incrementColValue() and then exit.
> For this purpose I installed my own shutdownHook(). My shitdownHook() thread
> 'sugnals' all the threads in my process that it is time to exit and then
> waits for them to complete.
> The problem is that HConnectionManager's shutdownHook thread also runs and
> shuts down all connections and IPC threads.
> My increment thread keeps waiting to increment and then times out after 240s.
> Two problems with this - the incrementColValiue() didn't go through which
> will increase the chances of inconsistency in my HBase data. And it too 240s
> to exit. I am pasting some of the messages that the client thread outputs
> while it tries contact the HBase server.
> Signalled. Exiting ...
> 2010-09-01 12:11:14,769 DEBUG [HCM.shutdownHook]
> zookeeper.ZooKeeperWrapper(787):
> <localhost:/hbase,org.apache.hadoop.hbase.client.HConnectionManager>Closed
> connection with ZooKeeper; /hbase/root-region-server
> flushing after 7899
> 2010-09-01 12:11:19,669 DEBUG [Line Processing Thread 0]
> client.HConnectionManager$TableServers(903): Cache hit for row <> in
> tableName .META.: location server hadoop2205.snc3.facebook.com:60020,
> location region name .META.,,1.1028785192
> 2010-09-01 12:11:19,671 INFO [Line Processing Thread 0]
> zookeeper.ZooKeeperWrapper(206): Reconnecting to zookeeper
> 2010-09-01 12:11:19,671 DEBUG [Line Processing Thread 0]
> zookeeper.ZooKeeperWrapper(212):
> <localhost:/hbase,org.apache.hadoop.hbase.client.HConnectionManager>Connected
> to zookeeper again
> 2010-09-01 12:11:24,679 DEBUG [Line Processing Thread 0]
> client.HConnectionManager$TableServers(964): Removed .META.,,1.1028785192 for
> tableName=.META. from cache because of content_action_url_metrics,\x080r&
> B\xF7\x81_T\x07\x08\x16uOrcom.gigya 429934274290948,99999999999999
> 2010-09-01 12:11:24,680 DEBUG [Line Processing Thread 0]
> client.HConnectionManager$TableServers(857): locateRegionInMeta attempt 0 of
> 4 failed; retrying after sleep of 5000 because: The client is stopped
> 2010-09-01 12:11:24,680 DEBUG [Line Processing Thread 0]
> zookeeper.ZooKeeperWrapper(470):
> <localhost:/hbase,org.apache.hadoop.hbase.client.HConnectionManager>Trying to
> read /hbase/root-region-server
> 2010-09-01 12:11:24,681 DEBUG [Line Processing Thread 0]
> zookeeper.ZooKeeperWrapper(489):
> <localhost:/hbase,org.apache.hadoop.hbase.client.HConnectionManager>Read
> ZNode /hbase/root-region-server got 10.26.119.190:60020
> 2010-09-01 12:11:24,681 DEBUG [Line Processing Thread 0]
> client.HConnectionManager$TableServers(1116): Root region location changed.
> Sleeping.
> ===
> It might be a good idea to only run the HCM shutdown code when all the
> HTables referring to it have been closed. That way the client can control
> when the shutdown actually happens.
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