MySQL cannot handle more than one incoming binlog at a time. The
facilities are just not in the code.
You also run into a nightmare if a database exists on BOTH masters (same
name on both systems) and the PK values of any tables (also with matching
names) overlap. If both masters update the "same" row at appx the same
time, we could run into deadlocking in the slave that didn't happen on
either master. It also means that the slave and at least one of the
masters will become out of sync (because the "other" master's changes
remain in the database) and replication is considered "broken" at that
point. It's a serious can of worms to handle multi-master replication.
Your two instances on one matching replicating to two separate masters is
not a multi-master replication (more than one master replicating with a
single slave) it's two single-master slave setups running on the same
machine. Close but not quite what the original post was looking for (I
don't think).
Shawn Green
Database Administrator
Unimin Corporation - Spruce Pine
David Griffiths <dgriffiths@stripped> wrote on 03/01/2006 04:34:26 PM:
> That's not entirely true.
>
> You can have two instances of mysql running on the slave, and dbA
> connects to one instance, and dbB connects to the other.
>
>
>
> Jeff, when you say, "different databases", do you mean that each
> master has a single mysql instance, and if you typed on M1,
>
> "show databases" you'd see (for example), "dbA"
>
> and if you did the same on M2, you'd see, "dbB"?
>
> If so, I wonder if there is another way to get around it:
>
> - create a virtual IP address that represents both masters. Use that
> virtual master in the my.cnf on the slave; each master has to
> have an identical replication account
>
> - put dbA and dbB on the slave
>
> - restrict replication from each master to their respective
> databases - "dbA" and "dbB" - ie don't replicate changes to the
> "mysql" database.
>
> The two masters appear as one (which overcomes the single-IP-address
> in the slave's my.cnf file), and each master has a different
> database inside the mysql instance, they aren't stepping on each others
toes.
>
> Just my 2 cents.
>
> David.
>
> Greg Donald wrote:
> > On 3/1/06, Jeff <jsmforum@stripped> wrote:
> >> Does anyone know if it's possible to replicate to a single slave from
> >> different databases on different masters?
> >>
> >> For instance:
> >>
> >> M1:dbA M2:dbB
> >> \ /
> >> rep rep
> >> \ /
> >> Slave
> >
> >
> > http://dev.mysql.com/doc/refman/5.1/en/replication-features.html
> >
> > <snip>MySQL only supports one master and many slaves.</snip>
> >
> >
> >
> > --
> > Greg Donald
> > Zend Certified Engineer
> > MySQL Core Certification
> > http://destiney.com/
> >
>
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