[Pgpool-hackers] Promoting any node as master with SR slaves follow

[Guillaume Lelarge]

Le 20/01/2011 20:15, Gilles Darold a écrit :
> Hi,
> 
> PgPool is a very cool project, when I start to use it this was in plan
> of PostgreSQL high availability and scalability using Pg 9.0 streaming
> replication. The objective is to have one PostgreSQL master with 10 or
> more slaves where I can load balance huge read only queries.
> 
> Everything works well until a failover happens. When the PostgreSQL
> master is down for some reason, PgPool force a failover to the next node
> in the replication line. The problem is not with PgPool but with
> PostgreSQL as there's no cascading replication yet. When the failover
> occurs, the next node is promoted as master by PgPool but all other
> slaves are still trying to connect/replicate to the old master. That
> mean that all these nodes have to be reconstructed from the new master
> again.
> 
> The other point is that PgPool always takes the next backend declared in
> his configuration file but maybe an other slave node has less
> replication lags and should be promoted instead of the next one.
> 
> All this make me do some work on PgPool source code as I think it may
> handle that easily. The patch do the following:
> 
> Add a PCP command to promote any node in the pgpool line as the new
> master : pcp_promote_node
> Add a follow master configuration option to call an external command
> when the failover is over.
> 
> So that if I run :
> 
>     pcp_promote_node 10 192.168.1.11 9898 postgres postgres 3
> 
> Node 3 is promoted as master and all other nodes are degenerated.
> 
> When the failover is ended PgPool fork a child to execute the command
> given in the follow_master_command successively for each node
> degenerated. The follow master command is simply a call to the
> pcp_recovery_node.
> 
> I've played some time with that patch and it works pretty well for me.
> 
> Well before going further I need to know if this is something useful
> that can be applied to PgPool? I also need help for testing under other
> modes than streaming replication.
> 

Am I wrong or you forgot to send the patch?


-- 
Guillaume
 http://www.postgresql.fr
 http://dalibo.com