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https://issues.apache.org/jira/browse/HBASE-6364?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13418397#comment-13418397
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nkeywal commented on HBASE-6364:
--------------------------------
That's a possible cause:
in HBaseClient#getConnection()
{noformat}
do {
synchronized (connections) {
connection = connections.get(remoteId);
if (connection == null) {
connection = new Connection(remoteId);
connections.put(remoteId, connection);
}
}
} while (!connection.addCall(call));
connection.setupIOstreams();
return connection;
}
{noformat}
Connection#addCall and Connection#setupIOstreams are synchronized. if
#setupIOstreams fails, it marks the connection as dead, remove it from the
connections list, and throws an exception. In #addCall it returns false if the
connection is marked as dead. So
case 1 -> Sometimes, we may add the call to a connection that will be marked as
dead:
Thread 1: create the connection, add it to the connections list, call addCall
Thread 2: get the connection, add it to the calls list
Thread 1: get into setupIOstreams, fails, and mark the connection as dead,
throws an exception, done
Thread 2: get into setupIOstreams, see that the connection is dead, done. The
call has been added to a dead connection
case 2 -> If we have a lot of threads on a dying connection, we will have:
Thread 1: goes until setupIOstreams
All other threads: get the connection from the list, wait on the synchronized
addCall
Thread 1: exit from setupIOstreams with an exception after 20 seconds (socket
timeout)
All other threads: call addCall, as the connection is dead, reloop
One of these threads will create a connection
One of these thread will win the race on addCall
One of them will win the race on setupIOstreams
Most of them should be waiting on addCall so reloop
So back to the case 1 or 2.
We would have the same behavior on pure hadoop client (ipc.Client), as the
implementation is similar, at least on 1.0.3.
Suraj, does this match your analysis? How many region servers and regions did
you have during your test? What's the client doing?
> 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
>
> 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 .META.
> 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 RS.
> 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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