Re: Replication

On Mon, 4 Feb 2002, mlw wrote:

> I re-wrote RServ.pm to C, and wrote a replication daemon. It works, but it
> works like the whole rserv project. I don't like it.
> 
> OK, what the hell do we need to do to get PostgreSQL replicating?

The trigger model is not a very sophisticated one. I think I have a better
-- though more complicated -- one. This model would be able to handle
multiple masters and master->slave.

First of all, all machines in the cluster would have to be aware all the
machines in the cluster. This would have to be stored in a new system
table.

The FE/BE protocol would need to be modified to accepted parsed node trees
generated by pg_analyze_and_rewrite(). These could then be dispatched by 
the executing server, inside of pg_exec_query_string, to all other servers
in the cluster (excluding itself). Naturally, this dispatch would need to
be non-blocking.

pg_exec_query_string() would need to check that nodetags to make sure
selects and perhaps some commands are not dispatched.

Before the executing server runs finish_xact_command(), it would check
that the query was successfully executed on all machines otherwise
abort. Such a system would need a few configuration options: whether or
not you abort on failed replication to slaves, the ability to replicate
only certain tables, etc.

Naturally, this would slow down writes to the system (possibly a lot
depending on the performance difference between the executing machine and
the least powerful machine in the cluster), but most usages of postgresql
are read intensive, not write.

Any reason this model would not work?

Gavin