Per their post about their MySQL backup solution[1], it sounds like they sort of do this? Although it's not a slave that's ready to be promoted to master, but somehow a cold standby that is not far off from being a hot standby based on how recent the binlogs are?
The wording is a bit cryptic, but it does seem that they definitely have hot standby-esque capabilities in place, in addition to long-term storage of their incremental/full backups.
The wording is a bit cryptic, but it does seem that they definitely have hot standby-esque capabilities in place, in addition to long-term storage of their incremental/full backups.
[1] - https://www.facebook.com/notes/facebook-engineering/under-th...