For the last year, Launchpad has been doing schema patches using a process we call ‘FDT’, short for Fast Down Time. We have applied 60 such patches, typically taking between 60 and 90 seconds each time, at 1000UTC, our scheduled daily 5 minute downtime window for DB patching.
Recently, we eliminated Slony from our environment, which has dropped the overhead of schema patches to ~6 seconds, and this gives us <10 second downtimes to apply schema patches. We’re taking advantage of this to add two new downtime windows at 0200 UTC and 1800 UTC. All three windows will be for 10 seconds. Hopefully you will never notice that we’re doing schema patches. But if Launchpad is offline for a few seconds at one of these times, you’ll know why – we’re busy rolling out a schema change to bring a new feature to life.