On Wed, 2011-10-05 at 12:22 +0200, Guillaume Lelarge wrote: > On Wed, 2011-10-05 at 10:13 +0100, Thom Brown wrote: > > On 5 October 2011 10:05, Guillaume Lelarge <[email protected]> wrote: > > > On Wed, 2011-10-05 at 09:38 +0100, Thom Brown wrote: > > >[...] > > >> This seems like it should be a very common setup, so does pgPool have > > >> provisioning for this, like having a 3rd pgPool to manage them > > >> somehow? > > >> > > > > > > No, it's not possible right now, and there's no discussion between > > > developers to do something like this (at least on pgpool-hackers). > > > > So no-one has ever configured pgPool to have true HA? Isn't there any > > kind of black magick trickery one can do with the existing config > > options to achieve this? > > > > I guess true HA really depends on your context. > > Say we have two data centers (DC1 and DC2), two PostgreSQL servers (PG1 > and PG2), and two pgpool servers (PGP1 and PGP2). I would have all users > access to the database through PGP1. Say that DC1 isn't available > anymore, what I would do is change the IPVS so that all users go through > PGP2, change PGP2 configuration so that it cannot access to PG1, and > make sure that PG2 is the new master. Which of course is not automatic, > there are a few steps that need manual work. > > But actually, what you are asking for is quite hard to have. > > > >> Also, if there was a primary and 2 standbys, and the primary goes > > >> down, which promotes standby1, how does standby2 then subscribe to > > >> standby1 automatically? And how does pgPool then know how to trigger > > >> failover on the next standby if the new primary fails? > > >> > > > > > > pgpool doesn't know which one to promote. It just calls a script when a > > > failover is needed. Now, you can have a "smart" script that will try to > > > understand which slave is the most uptodate, and promote only this one. > > > Keep in mind that the script is really executed when a node is detached, > > > meaning every node, even slaves one. So your script needs to check if > > > the detached node is the master one. > > > > > > In your example, for standby2 to follow standby1 (if standby1 is the new > > > master), pgpool executes a script (see follow_master_command option). > > > > Ah okay, I'll look into that. > > > > I'm interested in knowing any issues you can found while working on > this. > > > >> And when I set up pgPool today with a primary and standby using > > >> streaming replication, queries only seemed to hit the primary. Any > > >> idea what I could have missed? > > > > > > Setting load balancing? and having enough clients hitting your database? > > > > > >> Aren't SELECT queries supposed to be > > >> randomly sent to one of the servers? I ran queries several times and > > >> never did any hit the standby. > > >> > > > > > > You almost surely did this with one or two clients only, which won't > > > work. Use pgbench with 10 or more clients. > > > > Yes, you're right. I had 3 clients connecting, mainly calling > > pg_sleep so I could monitor it in pg_stat_activity on both servers. > > > > >> Just to note, the config changes were something like this: > > >> > > >> failover_command = '<command to put trigger file on 1st standby' > > >> backend_* = <these ones are all commented out as I'm only using pgPool > > >> for load balancing> > > >> replication_mode = false > > >> load_balance_mode = true > > >> replicate_select = false > > >> backend_hostname0/port0... = <this was set to the primary> > > >> backend_hostname1/port1... = <this was set to the first standby> > > >> > > > > > > So you set the load balancing mode. I guess you didn't have enough > > > clients. > > > > At least you didn't spot anything horribly wrong with these options. > > > > Nope, seems good to me. > > > So in load balancing mode, is backend_*0 regarded by pgPool to be the > > primary, or is pgPool clever and polls the servers to figure this out? > > > > You mean, in master_slave mode. AFAIR, yes, it is. But I'll check. >
And I was wrong. At least when you first start pgpool. -- Guillaume http://blog.guillaume.lelarge.info http://www.dalibo.com _______________________________________________ Pgpool-general mailing list [email protected] http://pgfoundry.org/mailman/listinfo/pgpool-general
