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Subject: Re: anyone with pgpool experience?
From: Perrin Harkins <perrin@elem.com>
To: David Nicol <davidnicol@gmail.com>
Cc: Jonathan Vanasco <modperl-list@2xlp.com>,
 modperl List <modperl@perl.apache.org>
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Date: Fri, 07 Apr 2006 22:51:28 -0400
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On Fri, 2006-04-07 at 21:16 -0500, David Nicol wrote:
> When I was trying to multiplex a single database connection to a
> room ful of clients that combination was reccommended to me by people
> on the DBI list.

I suspect most of them have never tried it.  It's a solution for
accessing a database that has no client available on your platform, but
it's not efficient.  It doesn't even keep the connections to the
database persistent, and every client connection still needs a separate
process.

Writing a pooling server that works as a proxy for all DBD's is pretty
hard, since they all have different client libraries and protocols.  A
non-blocking I/O approach would probably work great, but you'd need
non-blocking client libraries for all the databases.

> If I was to write a DBI multiplexer that simply serialized requests in order
> I would hope I was working against a database that could have multiple
> open result streams at once

I'm not sure where the idea of serializing requests came from, but
that's not going to be a viable solution for anyone with significant
traffic.  All of the popular databases handle parallel requests very
well.

If you run a proxy server in front of mod_perl, there's typically no
need to worry about pooling.  Apache does a good job of managing how
many mod_perl processes are running, and ones that don't hit mod_perl
will not tie up database connections.  The only exception is when you
have mod_perl handlers that do a lot of work but don't need a database
connection.  Those could be isolated on a separate mod_perl server if
necessary.

- Perrin