[pgpool-general: 4519] Worker Processes Exit and Are Not Re-spawned

Mike Neir mike at liquidweb.com
Sat Mar 5 09:43:55 JST 2016

Greetings pgpool devs and users,

I am attempting to re-create a postgres 9.2 + pgpool setup that a former
co-worker created so that I may become more familiar with the setup process
and so it can be properly documented. I am configuring a two-node test lab
using streaming replication, where the postgres WAL sender handles writes,
and both the WAL sender and receiver can handle reads.

I believe I have everything configured properly except for one vexing
issue. When running queries through pgpool, even simple status queries, the
workers will eventually die, having reached their internal connection
limit. This is expected, but pgpool does not seem to be forking another
worker to replace it, and that behavior eventually results in pgpool not
being able to handle queries due to a lack of workers. This manifests in
the logs as follows:

2016-03-04 18:27:50: pid 8754: FATAL:  child exiting, 500 connections
2016-03-04 18:27:50: pid 8303: LOG:  child process with pid: 8754 exits
with status 512
2016-03-04 18:27:50: pid 8303: LOG:  child process with pid: 8754 exited
with success and will not be restarted

I have not yet got to the point of importing data into postgres. I can
manifest this condition with repeated execution of the following command:
 $ psql -h localhost -U monitor postgres -c "SHOW pool_nodes;"

The behavior is the same on both nodes, regardless of whether it is a WAL
sender or recevier.

I've attempted to dig through the sources to find the scenario that would
tell pgpool that not forking a replacement worker is proper behavior, but
my C is *very* rusty, and I ran out of patience long before I understood
what leads to that condition.

In short, I'm looking for insight on what configuration directives could
lead to that behavior, and how to correct it.

Environment Details:
- Each node is a VM running CentOS 6.7, 64-bit
- Each node is running postgres 9.2.15 (latest version available),
installed via pgdg92 yum repository
- Each node is running pgpool-II-92 3.5.0-1 (latest version available),
installed via pgdg92 yum repository
- I can provide the pgpool or postgres configurations if need be, but since
they are lengthy, I will wait until they're requested.

Mike Neir
Infrastructure Administrator
Liquid Web, Inc.
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