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From colonelx <>
Subject Re: JDBC Master Slave Question
Date Tue, 30 Jun 2009 15:01:44 GMT

I got to try out the scenario I described above (ie) physically remove the
network cable from the Master.

Basically the database did not realize that the client had disconnected
and there was still a lock on the database table, (which was now an invalid
stale lock), and would 
never get released.

After some further digging I realised that there was an issue raised about
and also explains the exact behaviour I experienced. 

I know that there's nothing that can be done really at the ActiveMQ level,
its more of a DB issue really. 
I did look into maybe setting the tcp_keepalive to a low value which might
force the (invalid)connection
to close quicker at a TCP level, but I didn't want to mess around with stuff
like that at such a low level.

Any lock options at the DB level were specific to the amount of time you
wait until you get a lock, 
not the amount of time you can hold onto it.

In the end I wrote a DB specific script which basically kills any sessions
for a particular IP, which in 
turn releases the lock and the slave can kick in.

If anyone knows of a different (perhaps better) way of implementing this
please let us know.

Gary Tully wrote:
> You have got to ask the JDBC driver or database documentation. I imagine
> there is a lock expiry option that can be tweaked.
> 2009/6/29 colonelx <>
>> Hi,
>> I have 2 brokers setup in a JDBC Master Slave Configuration.
>> Each broker is on a different machine. BoxA and BoxB
>> The database is also on a different machine BoxC. (mysql 5.1)
>> The failover is working fine when I manually kill any instance of
>> ActiveMQ
>> on BoxA or BoxB. (Ctrl-C)
>> However, can anyone tell me what will happen if the if the Master
>> instance
>> looses its network connection ?
>> Will its lock on the database get dropped immediately ? or will it still
>> hold a (now invalid) lock on the database ?
>> I ask this, because if this happens , there could possibly be a condition
>> where the slave won't ever be able to get a lock on the database because
>> the
>> master has lock which did not get correctly released and manual
>> intervention
>> would be needed in order to fix up the problem.
>> I know that I could test this by plugging in and out the physical network
>> connections, but I'm not really in a position to do this on any of the
>> above
>> boxes.
>> Thanks.
>> --
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