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From Joshua Cohen <jco...@apache.org>
Subject Re: Review Request 45467: [PROTOTYPE] Add support for DB migrations and rollbacks.
Date Wed, 30 Mar 2016 18:14:14 GMT


> On March 30, 2016, 5:59 p.m., Bill Farner wrote:
> > src/main/java/org/apache/aurora/scheduler/storage/log/SnapshotStoreImpl.java, line
180
> > <https://reviews.apache.org/r/45467/diff/1/?file=1318681#file1318681line180>
> >
> >     As i read this, i found myself wishing for something that appears to be [`FileMigrationLoader`](https://github.com/mybatis/migrations/blob/master/src/main/java/org/apache/ibatis/migration/FileMigrationLoader.java)
but with the ability to load resources from the classpath.
> >     
> >     Have you given any thought to using that instead?

Are you saying you'd prefer migrations be stored as sql scripts rather than classes? It think
it would be possible to write something on top of `FileMigrationLoader` that did that, but
I actually kind of prefer the class-based representation since we want to define both up and
down scripts. I don't love the way the file-based scripts represent both in the same file
with an `@UNDO` annotation; this seems like it could potentially be brittle.


- Joshua


-----------------------------------------------------------
This is an automatically generated e-mail. To reply, visit:
https://reviews.apache.org/r/45467/#review126151
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On March 30, 2016, 3:41 a.m., Joshua Cohen wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/45467/
> -----------------------------------------------------------
> 
> (Updated March 30, 2016, 3:41 a.m.)
> 
> 
> Review request for Aurora, Maxim Khutornenko and Bill Farner.
> 
> 
> Repository: aurora
> 
> 
> Description
> -------
> 
> THIS CODE IS NOT INTENDED TO BE COMMITTED.
> 
> This is just a spike to show a proof of concept for how we can effect automatic migrations
and rollbacks of the H2 schema. The code is very sloppy, please use this to further the discussion
on the mailing list about migrations. If we agree this methodology is acceptable, I'll clean
this up and send out an actual review.
> 
> That said...
> 
> The general gist here is:
> 
> 1. Use MyBatis Migrations which has built in support for specifying an up and a down
script for db changes and also makes it easy to locate all existing migrations on the classpath.
> 2. When applying a migration, write the downgrade script to the changelog table in the
database.
> 3. Before actually applying migrations, check all changes in the changelog table. If
the corresponding migration does not exist on the classpath, we assume this is a rollback
and run the downgrade script from the changelog table and delete the corresponding changelog
row.
> 
> 
> Diffs
> -----
> 
>   build.gradle ad5ec5c4afe4dd5c2189d0680692a7409f0417a9 
>   examples/vagrant/upstart/aurora-scheduler.conf 120b89a1dc10a259940cb9527eb2517f19d04471

>   src/main/java/org/apache/aurora/scheduler/http/api/security/HttpSecurityModule.java
e32862034a1ad47dae8fff89cb04deb34ccd90e2 
>   src/main/java/org/apache/aurora/scheduler/storage/db/DbModule.java baf460e987d0a6ba2810507695fe118b6b502f87

>   src/main/java/org/apache/aurora/scheduler/storage/db/migration/V001_CreateUnifiedContainerTables.java
PRE-CREATION 
>   src/main/java/org/apache/aurora/scheduler/storage/log/SnapshotStoreImpl.java 6fee2510d044515e0704cf20ec0ba77231050ec4

> 
> Diff: https://reviews.apache.org/r/45467/diff/
> 
> 
> Testing
> -------
> 
> I manually verified in vagrant that this works as expected for upgrades with migrations,
upgrades without migrations and rollbacks.
> 
> 
> Thanks,
> 
> Joshua Cohen
> 
>


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