So we've got a script for this but it needs some tidying up. Would be nice to have this info somewhere so we can tell when the numbers diverge.

I've rolled Cirrus out to more wikis so the script is more useful than before. I've also fixed some math problems so we can get better data.

Maybe alert when we're > 40%? That's almost always a problem on our end. Less than that and you could very easily hit a wiki with a high redirect:page ratio and alert pointlessly.

Bleh, this script isn't all that useful. See for example:

demon@terbium:~$ mwscript extensions/CirrusSearch/maintenance/checkCounts.php zhwikibooks
SiteStats=12273
Elasticsearch=7258
Percentage=51%

But I just finished a force reindexing of this entire wiki to prove my point...this is hard to measure :(