[Mediawiki-l] is there any benefit from having multiple wikis on the same server run on different mysql daemons?

Brion Vibber brion at pobox.com
Tue Jan 11 20:41:09 UTC 2011

On Tue, Jan 11, 2011 at 2:27 PM, Jim Hu <jimhu at tamu.edu> wrote:

> As the number of wikis we host increases, I worry about our single mysql
> server becoming a bottleneck.  I assume that by modifying $wgDBserver  in
> the different copies of LocalSettings.php, I can point each wiki to a
> different port that is running a different instance of mysql.
> But is this worth doing?  My concern is that when we do db intensive stuff
> on wiki A, wikis B...X will underperform.

In most cases, the only reason to run multiple MySQL instances is because
they're running on separate machines.

It'll almost certainly be much better to run only a single MySQL daemon
instance per host. Multiple instances on the same host would be doing the
same work *plus* additional work, as they'd each individually be maintaining
their own in-memory data caches, file access, etc. If your memory sizes are
too large, you'll hit swap and performance will be completely destroyed; if
your memory sizes are too small, you won't be using the full capacity of the

A single instance will generally be able to much more reasonably partition
resources according to usage. (A database that is never used need not take
up any memory; a database that is hugely used can use as much key cache
memory etc as it needs -- but must negotiate for that space with the other
things being done.)

-- brion

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