[Mediawiki-l] Mediawiki clusters

[Brion Vibber]

Daniel J McDonald wrote:
> Ok, I get it.  The master is listed in the wgDBServer variable, and the
> slaves in the wgDBServers array of arrays.  Upon failure of the master,
> it's a manual process to get writes working again,

Yes; we're not losing sales if the site's partially broken for a few minutes, so
it hasn't yet been worth it to invest time and money in setting up automatic
transparent failover for something that's very rare.

> but reads should function fine.

Likely not; because reads need to function properly even when slaves are
slightly lagged, some items will check the master. For instance, on a page view
the tiny 'page' record is read from the master, then revision metadata, text,
and link-coloring information are pulled from a slave. Otherwise you can edit a
page and have it serve you back the previous version -- which we don't want then
stuck in a cache!

-- brion vibber (brion @ pobox.com)

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