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From cobrien <>
Subject Re: Noob Questions - Fail-over / Redundancy Help.
Date Sun, 04 Jul 2010 00:23:21 GMT

For Oracle, the  master instance of ActiveMQ obtains a lock the database
using a "select for update"  SQL statement. 
It appears that when you pull the plug, the data store does not detect the
stale connection in a  timely enough  fashion for your requirements. 
You can shorten the time needed to detect the stale connection by tuning the 
keepAlive TCP parameters ( OS specific) to meet your uptime requirements. 
When using oracle, setting  'ENABLE=BROKEN' in the TNS  ora  will enable 
use of the keepAlive packets.
Oracle also allows you to ping the client at regular intervals set by
sqlnet.expire_time (in minutes!). 

As always, do your testing in  an environment that   mimics your production
environment first. You may have to use trial and error  to find the right
settings for your OS and data store.

Happy Coding
ActiveMQ reference guide at

ejosterberg wrote:
> I'm having a hell of a time with setting up fail-over / redundancy with
> activemq 5.3.0
> I've tried using Oracle as a shared backend and fail-over works fine if I
> shutdown the activemq process on the active or hot host. But if I yank the
> power cord from the host that's the active or hot host a database lock
> remains blocking any of the slave or backup hosts from taking over as a
> primary or hot host.
> I've tried nfsv4 on linux redhat 5.5 and the timeouts are taking forever.
> I'm using the following for mounting options:
> nfs4
> rw,vers=4,rsize=32768,wsize=32768,hard,intr,proto=tcp,timeo=150,retrans=3,sec=sys
> nfs seems to be the best option so far. However when I was testing
> yesterday, killing the host power again, I didn't see the failover after
> waiting 25 minutes and gave up hope and left the building for lunch only
> to return an hour later and finding we were back up and processing on a
> slave/backup instance.  I assume I need to either tune tcp or nfs to get
> faster results.
> Any advice?
> What's the best option for prompt fail-over for my mission critical
> application. Downtime not exceeding 6 minutes a year is the expectation to
> meet.
> Thanks!

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