[Pgcluster-general] Question about setting up PGCluster

[Holger Lehmann]

Am Donnerstag, 1. November 2007 15:40:00 schrieb Sean Brown:
> On Nov 1, 2007, at 10:24 AM, Holger Lehmann wrote:
> > Hi Sean,
> >
> > Am Donnerstag, 1. November 2007 15:13:24 schrieb Sean Brown:
> >> I am working on setting up a PostgreSQL cluster using PGCluster. I
> >> have one question about the replication server.
> >>
> >> Is the replication server supposed to run on another system or is it
> >> a daemon that runs on each Node? If it is supposed to run on a
> >
> > only one pgreplicate instance is needed, although you can run more
> > than one if
> > you want to be failsafe. Where you start them is completely up to
> > you. You
> > can start them on the same machine where your postgresql runs or on
> > another
> > machine.
> >
> >> separate system can anyone provide pointers on sizing the system?
> >
> > Gee, for pgreplicate, make some space for the logfile, you need
> > some good I/O
> > troughput, make shure memory is not too tight. It all depends on
> > how many
> > data must be replicated in what time ... I guess you might want to
> > play
> > around with pgcbench (several times in a loop) and see what happens.
>
> Ok, so if the idea is that we don't loose any data in the event that
> one node goes down, and when it comes back it can be restored to

That depends on how you "write" data to your databases.

> where it should be and I don't want (currently) a separate machine to
> run pgreplicate I would choose to run pgreplicate on each node in the
> cluster.

on the crashed node do:
pg_ctl .... -o "-i -R" 
(or instead of -R use -r or -u, whateever you like). This will resync your 
formerly crashed cluster server like this:
- crashed node talks to pgreplicate: "Hi, I am back, please resync me"
- pgreplicate talks to a working node to now become the "master" for the time 
being and to the crashed node to become the salve
- nodes sync the filesystem files directly using rsync over ssh, so make sure 
you have that one setup perfectly (BTW: I used ssh -2 instead of ssh -1) and 
no password or hosts prompts happen between any of the nodes anymore (logging 
in spree ...)
- After a successful 2-stage sync, your crashed node is back up again and 
working

>
> Do I understand and have that straight?
>
> >> I'm planning on setting up a Master/Slave Cluster so I won't be using
> >> the load balancer.
> >
> > Um, sorry, Master-Slave Replications are this way:
> > http://pgfoundry.org/projects/slony1/ (Slony-I), just kidding.
> > PGReplicate is
> > a full Multi-Master Replicator and cannot be configured to be a
> > Master-Slave
> > Replicator. You can force you applications to behave so, but you do
> > not need
> > to :-)
>
> There were other reasons why Slony wasn't going to work out for us so
> yes, while we could set up multimaster, we will be choosing not to
> right now.

:-)

>
>
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Mit freundlichen Gruessen,
- H. Lehmann

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