Re: PG on two nodes with shared disk ocfs2 & drbd

Thank you for your detailed information about HA and LB. First of all it's a
pitty that there is no built-in feature for LB+HA (both of them,
simultaneous).
In my eyes, the pgpool2/3-solution has to much disadvantages and
restrictions.
My idea was the one, that john described: DML and DDL are done on the small
box and reporting on the "big mama" with streaming replication and hot
stand-by enabled. the only problem is that we use temp tables for reporting
purposes. i hope that the query duration impact with not using temp tables
will be equalized through running dml/ddl on the small box.

I think, this will be the final configuration:
- drbd with multi primary (ocfs2) as archive location for the primary node
- streaming replication and hot stand-by

this is a good howto to get real high availability when the primary node
goes down, but for now I'm going to deploy the described configuration with
manual fail over.
http://www.howtoforge.com/how-to-set-up-an-active-passive-postgresql-cluster-with-pacemaker-corosync-and-drbd-centos-5.5

Regards,
Jasmin

2011/2/27 Andrew Sullivan <ajs(at)crankycanuck(dot)ca>

> On Sun, Feb 27, 2011 at 12:10:36PM -0800, John R Pierce wrote:
> > are made to the master server, but reads are done to either. note you
> > do NOT want to use block level replication like drbd for this as the
> > drbd slave can not be actively mounted, nor could the slave instance of
> > postgres be aware of changes to the underlying storage, rather you would
> > use the streaming replication built into postgresql 9.0.
>
> Note that with drbd, you can have a piece of hot standby hardware
> sitting there to take over the filesystem in real time, in the event
> the original master blows up or something. My experience with systems
> designed like this is that they are a foot-bazooka: the only real
> utility I ever saw in them was to increase on-call hours for sysadmins
> after they blew off their own foot (and too often, my database) doing
> something tricky with the standby server. If it were me setting it
> up, I'd think the streaming replication approach a better bet. Not
> that anything will save you when someone else has root and decides to
> play with a production server.
>
> I believe that Greenplum sells a system based on Postgres that is
> supposed to do some kind of distributed cluster thing. I don't
> understand the details and it's been a long time since I had any look
> at it. I think it's intended to compete in the scalability rather
> than the availability market. Maybe someone around here knows more.
>
> The only people I'm aware of who really do this sort of thing for
> availability are Oracle with RAC, and Oracle with some mostly-works
> clustering stuff in MySQL. I have never met a happy customer of the
> former, but I've heard some people tell me it's real impressive
> technology when it's working. (The unhappy people seemed mostly
> unhappy because, for that kind of coin, they would like it to work
> most of the time. I know at least one metronet deployment that didn't
> work even once for two years.) In the case of the MySQL stuff, there
> are some trade-offs in the design that make my heart sink. But maybe
> for the OP's application it will work.
>
> A
>
>
> --
> Andrew Sullivan
> ajs(at)crankycanuck(dot)ca
>
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