Gary Tully uttered:
the keepAlive kicks in after the start() has successfully obtained the
lock, so a slave should just block, but a master should check the lock
status every period. By default it does an update using the connection
that has a pending transaction.
Ah, right, the keepAlive is for extant locks, not for keeping-alive connections
that are waiting for a lock. Which is, in hindsight, exactly what the name suggests.
It may be that that update has no need to hit the server till a
commit... not sure. May depend on the driver. But it should be
sufficient to validate the jdbc connection.
I cannot see a way to validate the jdbc connection while the slave is blocked
waiting for a response to its SELECT FOR UPDATE as the validation can only be
done on idle connections and the connection is not idle, it is actively waiting
for a response to its query. Even removeAbandoned won't touch it, as . . . it
hasn't been abandoned.
Have peek at the source:
http://svn.apache.org/viewvc/activemq/trunk/activemq-core/src/main/java/org/apache/activemq/store/jdbc/DefaultDatabaseLocker.java?view=markup
Yes, sorry -- I should have done this earlier. But it's so long since I've coded
Java that I assumed finding the right bit would take me a geological age.
Looking at that nice while loop, it occurs to me that another approach that
would work, would be to alter the SQL used to grab the lock to so that it won't
wait indefinitely, eg:
SELECT * FROM ACTIVEMQ_LOCK FOR UPDATE WAIT 300
From looking at http://activemq.apache.org/schema/core/activemq-core-5.5.0.xsd,
I cannot see a way to supply this SQL in config. Do you happen to know whether
this is possible?
Meanwhile, I shall get onto our hosting company about the half-open connection.
Thanks again fro your help,
Alex.
On 25 May 2012 13:36, Alex Hooper <ahoo...@bmjgroup.com> wrote:
Gary Tully uttered:
[snip]
In your setup, it is odd that the dropped connection does not cause
the lock keepAlive to fail and the broker to terminate. It should,
unless there are tcp level options that need to kick in to see the
half close. Or some connection pool config that can pick up on the
failure, there are some validate options on commons jdbc pool that
could help there.
[snip]
Hopefully the above will help, but start with determining why in your
current setup, the lock keepalive is not triggering for you when the
connection is dropped because that is a little odd. unless you have
the
org.apache.activemq.store.jdbc.JDBCPersistenceAdapter#setLockKeepAlivePeriod
= 0.
How exactly does the lock keepalive mechanism work? I'm explicitly set it in
the xml config now:
<jdbcPersistenceAdapter brokerName="prod-s01"
dataDirectory="${activemq.base}/data" dataSource="#oracle-ds"
useDatabaseLock="true" lockKeepAlivePeriod="10">
<statements>
<statements stringIdDataType="VARCHAR(128)" />
</statements>
</jdbcPersistenceAdapter>
But once the instance has started and issued its initial lock-requesting
query, there is no further TCP activity at all. Maybe I've misunderstood the
intent of this function; that's far from unlikely.
Alex.
On 24 May 2012 11:45, Alex Hooper <ahoo...@bmjgroup.com> wrote:
Hi,
We are running activemq 5.5.1 in an active/passive failover configuration
with JDBC Persistence to an Oracle backend. The default strategy for
determining whether the current master has failed is for the secondary
server to attempt to get a lock on the database table, waiting
indefinitely
for the lock to be granted.
This is not working (at least in our context) as, after a relatively
short
time in operation (a handful of hours at most) the connection to Oracle
is
dropped. Activemq doesn't notice this, so the secondary sits there
happily
waiting for a lock it can now never get and, in the event of a failure,
won't serve any clients as it is not a master.
Is there some way to change the decision mechanism to, eg, a polling
strategy? Or can anyone suggest another resolution to this problem?
Alex.
--
Alex Hooper
Operations Team Leader, BMJ Group, BMA House, London WC1H 9JR
Tel: +44 (0) 20 7383 6049
http://group.bmj.com/
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Alex Hooper
Operations Team Leader, BMJ Group, BMA House, London WC1H 9JR
Tel: +44 (0) 20 7383 6049
http://group.bmj.com/
_______________________________________________________________________
The BMJ Group is one of the world's most trusted providers of medical
information for doctors, researchers, health care workers and patients
group.bmj.com. This email and any attachments are confidential. If you
have received this email in error, please delete it and kindly notify us.
If the email contains personal views then the BMJ Group accepts no
responsibility for these statements. The recipient should check this email
and attachments for viruses because the BMJ Group accepts no liability for
any damage caused by viruses. Emails sent or received by the BMJ Group may
be monitored for size, traffic, distribution and content. BMJ Publishing
Group Limited trading as BMJ Group. A private limited company, registered
in England and Wales under registration number 03102371. Registered office:
BMA House, Tavistock Square, London WC1H 9JR, UK.
_______________________________________________________________________
--
Alex Hooper
Operations Team Leader, BMJ Group, BMA House, London WC1H 9JR
Tel: +44 (0) 20 7383 6049
http://group.bmj.com/
_______________________________________________________________________
The BMJ Group is one of the world's most trusted providers of medical
information for doctors, researchers, health care workers and patients
group.bmj.com. This email and any attachments are confidential. If you have
received this email in error, please delete it and kindly notify us. If the
email contains personal views then the BMJ Group accepts no responsibility for
these statements. The recipient should check this email and attachments for
viruses because the BMJ Group accepts no liability for any damage caused by
viruses. Emails sent or received by the BMJ Group may be monitored for size,
traffic, distribution and content. BMJ Publishing Group Limited trading as BMJ
Group. A private limited company, registered in England and Wales under
registration number 03102371. Registered office: BMA House, Tavistock Square,
London WC1H 9JR, UK.
_______________________________________________________________________
