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From "nkeywal (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-6364) Powering down the server host holding the .META. table causes HBase Client to take excessively long to recover and connect to reassigned .META. table
Date Sat, 28 Jul 2012 09:42:35 GMT

    [ https://issues.apache.org/jira/browse/HBASE-6364?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13424308#comment-13424308

nkeywal commented on HBASE-6364:

Thanks Suraj. So it seems that we have the root cause. You're right, on ipc.Client it's less
likely to occur. Only the NN could have the issue I think, and as the hot failover is not
yet deployed in production, it has not been an issue so far. I will ping Todd on this to see
what he thinks.

The only strange thing is that when tested on the 0.96 + minicluster, I have the issue but
many threads seem to be able to 'escape', i.e. manage to do the 'addCall' between two blocking
calls to setupIOstreams. But it could be a pure multithreading hazard. And I haven't been
able to find a better cause than this.

I will propose a patch, likely end of next week. Suraj, If you have some time available to
validate it on your env, it would be great.
> Powering down the server host holding the .META. table causes HBase Client to take excessively
long to recover and connect to reassigned .META. table
> -----------------------------------------------------------------------------------------------------------------------------------------------------
>                 Key: HBASE-6364
>                 URL: https://issues.apache.org/jira/browse/HBASE-6364
>             Project: HBase
>          Issue Type: Bug
>          Components: client
>    Affects Versions: 0.90.6, 0.92.1, 0.94.0
>            Reporter: Suraj Varma
>            Assignee: nkeywal
>              Labels: client
>         Attachments: stacktrace.txt
> When a server host with a Region Server holding the .META. table is powered down on a
live cluster, while the HBase cluster itself detects and reassigns the .META. table, connected
HBase Client's take an excessively long time to detect this and re-discover the reassigned
> Workaround: Decrease the ipc.socket.timeout on HBase Client side to a low  value (default
is 20s leading to 35 minute recovery time; we were able to get acceptable results with 100ms
getting a 3 minute recovery) 
> This was found during some hardware failure testing scenarios. 
> Test Case:
> 1) Apply load via client app on HBase cluster for several minutes
> 2) Power down the region server holding the .META. server (i.e. power off ... and keep
it off)
> 3) Measure how long it takes for cluster to reassign META table and for client threads
to re-lookup and re-orient to the lesser cluster (minus the RS and DN on that host).
> Observation:
> 1) Client threads spike up to maxThreads size ... and take over 35 mins to recover (i.e.
for the thread count to go back to normal) - no client calls are serviced - they just back
up on a synchronized method (see #2 below)
> 2) All the client app threads queue up behind the oahh.ipc.HBaseClient#setupIOStreams
method http://tinyurl.com/7js53dj
> After taking several thread dumps we found that the thread within this synchronized method
was blocked on  NetUtils.connect(this.socket, remoteId.getAddress(), getSocketTimeout(conf));
> The client thread that gets the synchronized lock would try to connect to the dead RS
(till socket times out after 20s), retries, and then the next thread gets in and so forth
in a serial manner.
> Workaround:
> -------------------
> Default ipc.socket.timeout is set to 20s. We dropped this to a low number (1000 ms, 
100 ms, etc) on the client side hbase-site.xml. With this setting, the client threads recovered
in a couple of minutes by failing fast and re-discovering the .META. table on a reassigned
> Assumption: This ipc.socket.timeout is only ever used during the initial "HConnection"
setup via the NetUtils.connect and should only ever be used when connectivity to a region
server is lost and needs to be re-established. i.e it does not affect the normal "RPC" actiivity
as this is just the connect timeout.
> During RS GC periods, any _new_ clients trying to connect will fail and will require
.META. table re-lookups.
> This above timeout workaround is only for the HBase client side.

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