[Pgpool-general] Several questions about pgpool

[Taiki Yamaguchi]

Hi,

Michael Ulitskiy wrote:
> Hello,
> 
> I'm using pgpool 3.1 and recently discovered several things that
> I'm not sure whether they're bugs or intended. I'd appreciate if someone
> can enlighten me on that.
> 1. Will pgpool fork additional children when the number of available children exhausted? 
> I was under impression it will, but the testing shows otherwise. Connecting clients just block
> until another client disconnects and pgpool process becomes available.

No. pgpool only forks children up to num_init_children. If there is no 
available child left, other connections will be queued until one of 
children will be available.

> 2. I thought that each pgpool process can serve "max_pool" number of usernames, multiplexing
> queries from different usernames. My testing shows it doesn't work. I set 
> num_init_children=4
> max_pool=4
> So i expect to be able to connect 16 clients using 4 different usernames, but after 4 clients
> connected (with different usernames) the 5th blocks waiting for available pgpool process.
> Is my understanding wrong? What is the purpose of max_pool parameter then?

pgpool child process *pools* up to max_pool number of connections (based 
on username, database, and protocol version). In your case, pgpool will 
pool at most 16 connections, but only 4 clients can connect concurrently.

> 3. I'm using load-balancing mode with replication done by slony-I. It seems when a client
> is connected, pgpool child opens connections to both primary and secondary backend
> which means that the number of concurrently served clients do not depend on the number
> of backends, right? In other words if I have num_init_children=32 then I won't be able to
> connect more than 32 clients regardless of number of backends I'm using?

As I answered in question 1, pgpool only serves connections up to 
num_init_children. The number of backends has nothing to do with it.

> 4. This is more a feature request. Have no idea how hard it is to do and whether it's possible
> in pgpool architecture. I'm expecting to have hundreds of clients connecting through pgpool
> to database cluster behind it. Some connections will be short-lived - several seconds, 
> while others will be relatively long-lived - minutes-to-hours, while others will be permanent - daemons.
> It would be really nice if pgpool children could process more than one connection multiplexing
> queries from different connection. Is it possible?

I am not sure why you need this feature. pgpool can handle hundreds of 
clients if you set your num_init_children to suit your application. If a 
short-lived client disconnects, child process which was serving that 
client will be available for the next incoming connection.


--
Taiki Yamaguchi

> 
> Thanks,
> Michael 
> _______________________________________________
> Pgpool-general mailing list
> Pgpool-general at pgfoundry.org
> http://pgfoundry.org/mailman/listinfo/pgpool-general
> 
> 
>