Re: pgpool-II (max_pool and num_init_children)

> I'm trying to get a handle on sane values for these two parameters.  I
> assume that they should somehow correlate  to my existing
> max_connections in my postgresql.conf file.  Anyone using pgpool-II care
> to comment?
>
> I'm sure it's a balancing act between how many connections you want
> verses how many cached connections you have, but not sure how to
> properly assess this issue.
>
> (I've tried posting to the pgpool list, but it's apparently unavailable
> at this time)

Here is an recommended rule:

max_pool*num_init_children <= (max_connections - superuser_reserved_connections)

Because num_init_children defines the max concurrent connections
pgpool-II can accept, you might want to keep num_init_children as
large as possible. In this case you could lower max_pool to as low as
1, which may cause performance degration because of low effect of
connection cache if you would have more than 1 user/database
combinations. However lower max_pool will not any error or any
problems except performance.

If you want to use query cancelation frequetntly, the formula above
will become:

max_pool*num_init_children*2 <= (max_connections - superuser_reserved_connections)

because you need extra connection to use query cancelation.
--
Tatsuo Ishii
SRA OSS, Inc. Japan
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