Simetrical wrote:
On Mon, Jul 7, 2008 at 8:55 AM, demon@svn.wikimedia.org wrote:
Log Message:
Cache the SVN version so we're not doing a filesystem read every time Special:Version (or APIQuerySiteInfo) asks for it.
This appears to mean that the version will be inaccurate for up to an hour after svn upping. This is a regression which could be potentially significant; it's fairly important to know the exact revision if an error is spotted right after an svn up. Is there any reason to think that the benefit is worth it? Operating systems do have disk caches, which are a lot faster than a memcached call if they get hit, and we're only talking about a vanishingly small minority of page views here anyway. I would suggest this be backed out unless this is causing a demonstrable performance problem.
We do a fair few filesystem reads on each request in the Wikimedia cluster, served from kernel cache, they're quite a bit faster than memcached. Obviously if you have your script directory on NFS, it's going to be slow, but still comparable to memcached. Maybe if the NFS server was overloaded or underpowered, then there would be an argument for it.
-- Tim Starling