Re: profiling connection overhead

From: Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc>
To: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Bruce Momjian <bruce(at)momjian(dot)us>, Andres Freund <andres(at)anarazel(dot)de>, pgsql-hackers(at)postgresql(dot)org, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Subject: Re: profiling connection overhead
Date: 2010-12-05 09:47:37
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On 12/01/2010 05:32 AM, Jeff Janes wrote:
> On 11/28/10, Robert Haas<robertmhaas(at)gmail(dot)com> wrote:
>> In a close race, I don't think we should get bogged down in
>> micro-optimization here, both because micro-optimizations may not gain
>> much and because what works well on one platform may not do much at
>> all on another. The more general issue here is what to do about our
>> high backend startup costs. Beyond trying to recycle backends for new
>> connections, as I've previous proposed and with all the problems it
>> entails,
> Is there a particular discussion of that matter you could point me to?
>> the only thing that looks promising here is to try to somehow
>> cut down on the cost of populating the catcache and relcache, not that
>> I have a very clear idea how to do that. This has to be a soluble
>> problem because other people have solved it.
> Oracle's backend start up time seems to be way higher than PG's.
> Their main solution is something that is fundamentally a built in
> connection pooler with some bells and whistles built in. I'm not
> sure "other people" you had in mind--Oracle is generally the one that
> pops to my mind.
>> To some degree we're a
>> victim of our own flexible and extensible architecture here, but I
>> find it pretty unsatisfying to just say, OK, well, we're slow.
> What about "well OK, we have PGbouncer"? Are there fixable
> short-comings that it has which could make the issue less of an issue?

well I would very much like to seen an integrated pooler in postgresql -
pgbouncer is a very nice piece of software (and might even be a base for
an integrated bouncer), but being not closely tied to the backend you
are loosing a lot.
One of the more obvious examples is that now that we have no flatfile
copy of pg_authid you have to use cruel hacks like:

to get "automatic" management of roles. There are some other drawbacks
as well:

* no coordination of restarts/configuration changes between the cluster
and the pooler
* you have two pieces of config files to configure your pooling settings
(having all that available say in a catalog in pg would be awesome)
* you lose all of the advanced authentication features of pg (because
all connections need to go through the pooler) and also ip-based stuff
* no SSL support(in the case of pgbouncer)
* complexity in reseting backend state (we added some support for that
through explicit SQL level commands in recent releases but it still is a


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