Re: [Skytools-users] WAL Shipping + checkpoint

On 26/08/2009 04:46, Mark Kirkwood wrote:
> Sébastien Lardière wrote:
>> Hi All,
>>
>> I've a cluster ( Pg 8.3.7 ) with WAL Shipping, and a few hours ago,
>> the master had to restart.
>>
>> I use walmgr from Skytools, which works very well.
>>
>> I have already restart the master without any problem, but today, the
>> slave doesn't work like I want. The field "Time of latest checkpoint"
>> from the pg_controldata on the slave keep the same values, but WAL
>> File are processed correctly.
>>
>> I try to restart the slave, but, after processed again all the WAL
>> between "Time of latest checkpoint" and, it does nothing else, latest
>> checkpoint stay at the same value.
>>
>> I don't know if it's important ( i think so ), and I can't fix it.
>>
> It is normal for it to lag behind somewhat on the slave (depending on
> what your checkpoint timeout etc settings are).
>
> However, I've noticed what you are seeing as well - particularly when
> there are no actual data changes coming through in the logs - the
> slave checkpoint time does not change even tho there have been
> checkpoints on the master (I may have a look in the code to see what
> the story really is...if I have time).
>

Yes, but the delay between the last checkpoint on the master and the
slave is very high, now ( 100 000 sec ), because the last checkpoint on
the slave was yesterday ( as far as pg_controldata is right )

Here a graph from our munin plugin :
http://seb.ouvaton.org/tmp/bdd-pg_walmgr-week.png

The blue line represent an average between two WAL processed on the
slave, and the green line, the delai between last checkpoint on the
master and the slave.

Maybe it's not some good indicator, but the green line let me think
there is problem.

Thanks,

--
Sébastien Lardière