Squash the havana migration scripts

[Kanagaraj Manickam]

Once heat is installed, admin runs "heat-manage db_sync" command, which will run all migration scripts (in ./heat/db/sqlalchemy/migrate_repo/versions) upto HEAD version. This is very much suitable for the upgrades/downgrades of heat versions.
But on the fresh installation, the db schema can be created directly in sqlalchemy way, instead of running through these migration scripts, which will speedup the operation and schema will be generated in single run.

This bug is filed to address it.

To fix, we could use following snippet of the code:

from sqlalchemy.ext.declarative import declarative_base
#engine = <create the engine here>
declarative_base().metadata.create_all(engine).
#stamp with head version

[Angus Salkeld (asalkeld)]

How much time does that really save?
It seems like an unnecessary optimisation to me
Also don't the migrations save the current migration in the db?
So doing what you suggest will break that?

[Kanagaraj Manickam (kanagaraj-manickam)]

As you have suggested over IRC, we could go with squash concept here to reduce the number of migrations to be within the range of versions from 'icehouse' as sated in https://wiki.openstack.org/wiki/Releases.

 we could use this bug to squash.

[Angus Salkeld (asalkeld)]

Let's find out what the process is for this.

1. how many can we do? havana/icehouse...
2. we probably need to leave placeholder scripts in place.
3. etc... - let's learn from other people/project's experience.

[Sergey Kraynev (skraynev)]

FYI: I have it with guys from nova. As feedback:
- it does not get huge benefit for us in performance
- we can get some errors/mistakes due to it's manual work (there is no any automatic script)
- it makes migrate history less clear (honestly, it's not big deal)
So I agree with Low status, and it can be done by anybody, who wants contribute to Heat.
Some advises can be gotten from dprince (he did the same thing in nova).
btw glance and cinder do not worry about this work.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/186291

[Kanagaraj Manickam (kanagaraj-manickam)]

Hi Qming, I was working on this as it got scheduled for Liberty-1 and i mentioned it in etherpad (https://etherpad.openstack.org/p/YVR-heat-contributor-meetup) as well.

Now, you have submitted an patch for it.
So, I'm concerned here that I lost the effort I had spent on this defect. And I would have been happy
if you have tried to let me know, before you start to work on it, which would effectively saved your effort as well !

[Qiming Teng (tengqim)]

Oh, Kanagaraj Manickam, I didn't realize that you were working on it when I signed up for this back in Vancouver.
Sorry for the conflicts caused.