[Pgpool-hackers] Major problem in find_primary_node()

[Tatsuo Ishii]

> Hi,
> 
> I've found something critical into the way that find_primary_node()
> detect if a node is a standby host and by deduction the primary node in
> streaming replication mode.
> 
> When it call "SELECT pg_is_in_recovery() AND pgpool_walrecrunning()" it
> always return false if pg_is_in_recovery = 'true' and
> pgpool_walrecrunning = 'false'. That mean that the host can be promoted
> as master, the situation will going worse if a failover occurs and
> PgPool takes this fake host as the master.
> 
> This is not a problem that can occurs easily but let check the following:
> 
> - Master has failover to node 1.
> - Node 0 is reconstructed but the primary_conninfo host in recovery.conf
> is wrong/broken for some reason.
> 
> At this stage, both nodes are running with PgPool status 2 and currently
> the only problem is that node 0 is not replicated from the master node.

This is not what observe. In this case I see node 0 is in status
3(down). If conninfo is broken in recovery.conf, postmaster won't
start up and keeps on saying "the database system is starting
up". What did you make a mistake in recovery.conf exactly?

> Then if a failover from node 1 occurs, PgPool will try to find a new
> master by querying "SELECT pg_is_in_recovery() AND
> pgpool_walrecrunning()" to all nodes, but as node 0 will return false
> because the wal receiver is not running, PgPool will take it as the new
> master, and very bad annoying things will happen from this point.
> 
> What I suggest is to try to find the master by finding a node that is
> not in recovery mode and where wal receiver is not running. This will
> allow a simple fix by changing the SQL query :
> 
> SELECT  pg_is_in_recovery() = 'f' AND pgpool_walrecrunning() = 'f';
>   or
> SELECT not pg_is_in_recovery() AND not pgpool_walrecrunning();
> 
> What's your opinion, if every one is ok with that fix I already have a
> patch for that.
> 
> Regards,
> 
> -- 
> Gilles Darold
> http://dalibo.com - http://dalibo.org
> 
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