launchpad-dev team mailing list archive

[Danilo Šegan <danilo@xxxxxxxxxxxxx>]

У пет, 02. 07 2010. у 06:09 +1000, Robert Collins пише:
> 
> Separately there is the whole strange {db-}devel thing, but that is
> also related to how rollouts are done. I understand that its that way
> because writing schema-migration-safe code is perceived to be too
> hard: has any team done it? I'd _love_ to see a lightning talk on that
> at the Epic.

We did our message sharing migration by extending a schema in a way that
allows us to develop new features while keeping the old ones that we are
deprecating.  For a few months, code had to support both schemas.  And
migration to the new model is not yet complete, even if it's been
running since the start of the year (ok, we're cross-analyzing a 100M
row table and reducing it to something like ~60M table).

Arguably, our change was too heavy a change and it's not reflective of
our day-to-day schema changes (we were changing the semantics and
referential relationships in the model), but I'd definitely say it was
very complex (not to mention that it's not fully done yet).  We'd still
do it for any other change, simply because, well, we have no other
option ("'scuse me, can we take LP offline for a week to do a bunch of
migrations please?").

I can imagine it being much easier for simpler schema extensions, but I
ain't gonna go through the effort while there is db-devel around. :)

Cheers,
Danilo