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From:Rick James Date:December 7 2010 11:52pm
Subject:Re: Limits to Multi-master replication?
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3+ Masters in a ring has virtually no practical use.
* No Performance gain...  All writes are done on all machines.
* Unreliable...  If one Master goes down, it is quite messy to fix the 
replication.

Can you do "sharding"?  That is, send different users to different 
Masters?  And make the affinity essentially permanent.  For BCP, etc, 
you could use Dual-master-single-writer for fast failover.

On 12/7/10 2:26 AM, Matt Wallace wrote:
> Hi Johan,
>
> On Tuesday 07 Dec 2010 10:14:38 you wrote:
>> I've had very bad experiences with multiple high-traffic drupal sites on a
>> single database; it behaves very badly. I can't comment on the other CMSes
>> you mention.
> Is that a single database or a single MySQL instance?  Each domain that we
> host has it's own database (and many have more than that!), so the table names
> are unique to that DB/CMS install.
>
>> The main thing you're going to be running into, I suspect, is the number of
>> writes - you can't scale that short of cross-machine partitioning, be it
>> horizontal or vertical. Maybe it's possible to use MMM or MySQL Proxy on
>> top of such a setup to give the appearance of a single host again, but I
>> imagine there would be complexities.
> We have dedicated Load Balancers to spread the traffic across multiple MySQL
> instances, hence the thinking behind multi-master replication - or have I mis-
> understood your point? :)
>
>> We have since shifted to heavy-duty machines running separate Xen VMs for
>> every site. Just beginnin with that, but hopes are that will give us the
>> independence we need to keep an overloaded site from pulling all the others
>> down with it.
> Hmmm, that's an interesting concept, I'll have a think about whether that's a
> possible solution here as well (although I don't much fancy running 24000 Xen
> instances!).
>
> Thanks,
>
> Matt
>

-- 
Rick James - MySQL Geek

Thread
Limits to Multi-master replication?Matt Wallace7 Dec
  • Re: Limits to Multi-master replication?Johan De Meersman7 Dec
    • Re: Limits to Multi-master replication?Matt Wallace7 Dec
      • Re: Limits to Multi-master replication?Johan De Meersman7 Dec
      • Re: Limits to Multi-master replication?Rick James8 Dec