Facebook's Fred Emmott works on benchmarking HHVM's performance when running various open-source PHP frameworks. This puts him in contact with MediaWiki's codebase. He wrote in to suggest that we experiment with using plain PHP files instead of CDB for the l10n cache. We should try that and see whether it improves performance.
- Enable array format on testwiki on Beta Cluster. (We used test2wiki in 2015, but I recommend we use testwiki this time, so that Beta Cluster gets it as well) – Similar to 7237148affb4 / https://gerrit.wikimedia.org/r/217702.
- Have Scap include testwiki as extra element in its loop over "pick a wiki per wiki version" for its invoking of _call_rebuildLocalisationCache. See also T105683, and https://gerrit.wikimedia.org/r/#/c/mediawiki/tools/scap/+/224520/5/scap/tasks.py for related changes that might be needed.
- Confirm it works in Beta Cluster.
- Enable array format for all wikis in Beta, except testwiki (inverse of before), and run that for a week or two to confirm there's no major issues with HHVM (or PHP 7).
- Enable array format for testwiki in production.
- (Temporary) Add magic switch to wmf-config to use array on any wiki, if and only if the array cache file is locally found. This is for during the transition. See also c9ff83c234f53 / https://gerrit.wikimedia.org/r/224562.
- Enable array for all wikis.
- Remove temporary switch.
- Remove extra element from Scap loop for rebuildLocalisationCache.