[pgpool-general: 1442] Re: removing nodes from pgpool without restarting

Tatsuo Ishii ishii at postgresql.org
Thu Feb 28 09:22:59 JST 2013

> Hi,
> I have set up pgpool 3.2.3 in master/slave mode with streaming replication and it works fine.  Now I want to use autoscaling to add and remove nodes as demand fluctuates. Scaling up works with no problems, but when I scale down, I want to remove the extra nodes from pgpool wiithout restarting.  What happens now is I call pcp_detach_node(), which changes the status from 2 to 3 for that node, but leaves it in the pool.  I also remove the backend from the config file and reload it, but that has no effect unless you restart pgpool.
> 1. Is there a way to just remove a node from pgpool?

No(without restarting pgpool).

> 2. If not, is it a problem to leave a number of nodes with status 3 in the pool?  The nodes themselves will have been terminated.

Should be no problem. Leaving those unused nodes in pgpool.conf will
cause problem when you restart pgpool though (they will trigger
immediate failover).

> 3. I see that when I detach a standby node, it calls the failover command - why?

Pgpool-II handles the failover event in uniform way. In fact the
difference between failover and detach is just the former is triggered
by detection of errors, while the latter is triggered by pcp command.
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp

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