[Buildbot] #2590: Use Alembic instead of SQLAlchemy-Migrate

[Buildbot trac]

#2590: Use Alembic instead of SQLAlchemy-Migrate
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Reporter:  dustin        |       Owner:
    Type:  project-idea  |      Status:  new
Priority:  major         |   Milestone:  0.9.+
 Version:                |  Resolution:
Keywords:  database      |
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Comment (by dustin):

 Alembic is a new Python dependency, and can be installed anywhere Buildbot
 can -- so the new dependency isn't an issue.

 I'd like to rewrite all of the existing migration scripts, with some glue
 in place to translate migrate versions (integers) into alembic versions.

 Regarding autogeneration and SQL statements -- one of the things I *do*
 like about sqlalchemy-migrate is that it moneypatches SQLAlchemy to
 support common operations like adding and removing columns.  I don't want
 to get to the point of writing raw SQL strings -- we have SQLAlchemy to do
 that kind of work for us -- but we'll need some functionality beyond what
 SQLAlchemy provides.

 The `buildbot upgrade-master` command allows users to *explicitly* upgrade
 their master.  Imagine the mayhem if someone accidentally started a newer
 version of Buildbot in a staging environment, but with the production
 database credentials, and it automatically upgraded the database.  That
 would certainly cause downtime as all of the un-upgraded production
 masters were suddenly using a newer database.  It might also mean data
 loss.

 So, the upgrade-master command is a way to ensure that users are explicit
 about when database upgrades are performed.

 Regarding "users lose data", I meant that a *broken* migration can easily
 lose data -- so testing will be important, as you said.

--
Ticket URL: <http://trac.buildbot.net/ticket/2590#comment:6>
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