On 2011-07-15 00:27, Robert Collins wrote:
As prep for https://dev.launchpad.net/LEP/FastDowntime the db schema
I appreciate that between now and the deployment side of this going
live we're going to be doing a little more work around each schema
patch with no immediate payoff - but it means we'll be able to go
straight into the fastdowntime process once its ready.
Thank you so much for pushing this through!
There _is_ an immediate payoff: your db patch gets deployed much faster.
We've been aching for this kind of flexibility.
I ran some numbers a few years back when I proposed weekly rollouts of
devel plus "live" DB patches. For a medium-sized change, live patches
took more work but the worst-case time to useful deployment was about
the same as the best-case time for our current scheme. Typical cases
were massively better. And that was with a limitation of one phase per
week; we're getting something much faster.
We'll learn how to write incremental patches. Meeting the 15s goal on a
cold database will be hard though, since we can't easily reproduce
results or try out tweaks. It might help if we could break a slave out
of replication to time a DB patch against a realistic cache.
Jeroen
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