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Re: Advice on running two database clusters on one server machine

From: "Peter Koczan" <pjkoczan(at)gmail(dot)com>
To: "Andreas Philipp" <andreas(dot)philipp(at)clinicauniversitariateleton(dot)edu(dot)co>
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: Advice on running two database clusters on one server machine
Date: 2008-06-19 07:16:54
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Lists: pgsql-admin
On Sun, Jun 15, 2008 at 12:11 PM, Andreas Philipp
<andreas(dot)philipp(at)clinicauniversitariateleton(dot)edu(dot)co> wrote:
> Hi all,
> We are implementing a hospital information system and a human
> resources/payroll processing system on two identical dedicated servers with
> two Xeon Quad Core processors and 32 GB RAM each, both servers being attached
> via FC to a SAN, and both applications running on PostgreSQL 8.3 / CentOS 51.
> We are wondering about the advisability to distribute the databases between
> the two server machines, both machines acting as active production systems
> for one application each, and as warm standby servers for the other, using
> WAL shipping to a second database cluster running on another port on each of
> the two server machines.
> What would be the performance cost of doing so, rather than running all
> databases on one database cluster on one machine, and using the second
> machine as a warm standby server for all databases of the two applications?
> What other considerations should we take into account? We have no prior
> experience with PostgeSQL administration, having run our previous systems on
> Windows Servers and MS SQL Server.
> Thanks to all for your input!

I've experimented a bit with this. Probably the biggest thing to keep
in mind is that different clusters don't play nice with resources,
especially shared memory. You're ostensibly cutting your available
memory in half by running two clusters on one machine.

Other things to keep in mind...they can't use the same user and group
data (so roles and passwords may be different and it's a bit of work
to keep them sync'd up if you would want that). You also have to
maintain two different sets of configs, have data located at two
different places, and listen to data on two different ports. It's
about double the basic administration.

I would recommend one cluster per machine for production machines, if
it works well for you, that is.


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