Paul J Stevens wrote:
I've probably asked this before however can someone remind me why mysql
master-master (innodb) replication is not recommend with dbmail?
It's not "recommended" with anything. By the very nature of it, there is
a potential very nasty race condition inherent in multi-master MySQL
replication. In practice you'd have to be extremely unlucky to encounter
it, but since there is no cluster-wide locking available in this setup,
it is a possibility. FWIW, I use it with multi-master replication. YMMV.
These conditions will not be very rare at all once you start putting
pressure on it.
But there is another reason in the imap requirements: UID values must be
strictly ascending within a mailbox.
Since these UID values are the autoincremented primary key on the
mailboxes table the only way to avoid collisions in the first place is
by stepping them differently on the separate masters, but doing that
will collide with the imap requirement I mentioned.
Hmm... I'll have to think about that case and try a few tests. Unless
there is a serious race condition encountered (which will only happen if
the same user has multiple simultaneous connections to separate
servers), I think the staggered auto-increments will still resolve
correctly (there will just be holes in the key-space, which I don't
think would cause problems).
I'm not saying it's a good idea, but I think the scope for a damaging
race condition is reasonably limited.
Gordan
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