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From "Prakash Khemani (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-2952) HConnectionManager's shutdown hook interferes with client's operations
Date Wed, 01 Sep 2010 19:15:53 GMT
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$TableServers(903):
Cache hit for row <> in tableName .META.: location server hadoop2205.snc3.facebook.com:60020,
location region name .META.,,1.1028785192
2010-09-01 12:11:19,671 INFO  [Line Processing Thread 0] zookeeper.ZooKeeperWrapper(206):
Reconnecting to zookeeper
2010-09-01 12:11:19,671 DEBUG [Line Processing Thread 0] zookeeper.ZooKeeperWrapper(212):
<localhost:/hbase,org.apache.hadoop.hbase.client.HConnectionManager>Connected to zookeeper
2010-09-01 12:11:24,679 DEBUG [Line Processing Thread 0] client.HConnectionManager$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$TableServers(857):
locateRegionInMeta attempt 0 of 4 failed; retrying after sleep of 5000 because: The client
is stopped
2010-09-01 12:11:24,680 DEBUG [Line Processing Thread 0] zookeeper.ZooKeeperWrapper(470):
<localhost:/hbase,org.apache.hadoop.hbase.client.HConnectionManager>Trying to read /hbase/root-region-server
2010-09-01 12:11:24,681 DEBUG [Line Processing Thread 0] zookeeper.ZooKeeperWrapper(489):
<localhost:/hbase,org.apache.hadoop.hbase.client.HConnectionManager>Read ZNode /hbase/root-region-server
2010-09-01 12:11:24,681 DEBUG [Line Processing Thread 0] client.HConnectionManager$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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