[Pgpool-general] Feedback on production system in master / slave mode

[Darcy Buskermolen]

On Friday 28 October 2005 10:03, Brad Nicholson wrote:
> Philippe MOREAU wrote:
> >Anyone having a feedback on pgpool being used in such a production
> >environment ?
> >
> >. slony-I used for database replication
> >. pgpool in master / slave configuration
> >. READ operations load-balanced two both servers
> >. WRITE operations only on primary node
>
> A couple of potential issues of the top of my head.
>
> First, consider this scenario
>
> 1)write to the slony master
> 2)read, pgpool balancer sends read to subscriber.
> 3)Event from 1) propagates via slony to subscriber
>
> This could be a very bad situation, depending on your application.  The
> data from step 1 has been written to the db, but the read in step 2 will
> not find it.

If you did your insert + select all within transaction blocks, then the query 
will only happen on the master.

>
> The other scenario, if you master database fails, pgpool will direct all
> the transactions to the subscriber.  All write transacations will fail
> (slony puts triggers on all subscribers to deny writes).
>
> This automatic failover may be good or bad, depending on your perspective.

-- 
Darcy Buskermolen
Wavefire Technologies Corp.

http://www.wavefire.com
ph: 250.717.0200
fx: 250.763.1759