Re: Replication

Well, AFAICT this kind of replication in postgres is not be named "out
of the box". Setting up the whole thing to work, and test it to really
work reliably is not exactly trivial, and you could have a number of
surprises (like when there's little activity, the last WAL stays at the
server and so the stand-by can be off by a considerable amount of time,
even if in terms of data quantity the difference is not that big). You
must master well scripting to write reliable scripts to handle the
process, though I think there are some examples around, but you still
need to customize them for sure.

What is missing is an easy way to set up the hot stand-by, without
requiring the user to do too much side-work.

I wonder if there is a way to set up a direct link between the standby
and the server and instead of copying files just send directly the WAL
data over by some background process ? The overhead of sending the data
directly should be similar with copying the files. Then the easiest way
to set up a standby would be to start up the stand-by server with some
standby options and giving the server's connection params, and then the
standby should make a special connection to the server requesting a data
dump + WAL from the data dump start on. Would this be reasonably simple
to implement ? I'm not at all familiar with postgres code or the C
language, so this is just wishful thinking.

Cheers,
Csaba.



On Tue, 2005-09-13 at 17:45, Russ Brown wrote:
> Simon Riggs wrote:
> > Barry,
> >
> > You can use PITR to archive transaction logs to a second server that is
> > kept in standby mode.
> >
> > This will cope with any number of tables and cope with dynamic changes
> > to tables.
> >
> > This is fairly straightforward and very low overhead.
> > Set archive_command to a program that transfers xlog files to second
> > server.
> > Then set restore_command on the second server to a program that loops
> > until the next file is available.
> > Switchover time is low.
> >
>
> Apologies for going slighly off topic, but isn't this basically how
> MySQL does replication? I ask because one of the arguments against
> moving to PostgreSQL in my organisation is 'no replication out of the
> box'. But if the above is true it seems that all that is required are a
> couple of scripts to handle log transfer and you have a form of
> replication out of the box right there.
>
> Or am I missing something?