Re: Version Control? - Mailing list pgsql-general
From | Peter Fein |
---|---|
Subject | Re: Version Control? |
Date | |
Msg-id | 42A9B40C.20502@pobox.com Whole thread Raw |
In response to | Re: Version Control? (Russ Brown <pickscrape@gmail.com>) |
Responses |
Re: Version Control?
Re: Version Control? Re: Version Control? |
List | pgsql-general |
Russ Brown wrote: > On 6/9/05, elein <elein@varlena.com> wrote: > >>On Thu, Jun 09, 2005 at 04:16:46PM -0500, John Browne wrote: >> >>>How would you handle the migration of the data with these user >>>scripts? Dump it to a temp table? >>> >> >>If your scripts are correct, you should be able to load >>your base scripts and apply each change script in order >>and have the result be the exact same database schema. >> >>If they are not, checkpoint with a schema dump and start >>again with the change scripts. Of course getting the >>scripts wrong is against the point of the whole exercise, >>but it is not easy and requires vigilance. >> > > > The big complexity for me is that the the database schema's state > should be stored along with the code that uses it: i.e. in CVS or > Subversion or whatever with the code. That way you have a consistent > snapshot of your complete system database at any given point in time > (minus the data itself). Developers will need to re-dump the schema > whenever they make a change to the datbase and commit it along with > everything else, but that's easily scriptable. > > Writing individual 'patch' scripts is fine for linear development, but > breaks down when dealing with a development environment that involves > branching. If two branches make changes to the database, each's patch > file would be written against the original version, which may not be > the case once the other patch has been apllied. What is needed is a > tool which will compare any two revisions of the schema and generate a > patch file that performs the migration. This is interesting... You'd want to be able to generate either a bunch of CREATEs to create a schema from scratch or a 'patch' of ALTER commands to move b/w arbitrary revisions or to a working copy (ie, a live DB). This implies you need to store an intermediate (non-SQL) representation in your repository (like the output of WBDiff mentioned previously). What's unusual is that your SQL-generating tool would need to checkout *both* versions of the representations to generate the patch. I can't think of any other problems that have this requirement - usually, you're relying on your version control software to generate such diffs for you. > This would obviously have to be pretty damn clever. Amongs the > difficulties would be ensuring that the patch applies changes in the > correct order (e.g. add column before adding foreign key). It's hard, > but I don't believe it's impossible. As an uninformed, off-the-wall idea, could one compare snapshots of the system tables to generate these diffs? I know next-to-nothing about these, but it seems like they'd contain the info you'd need. This still doesn't solve the problem of identifying which tables should have their *data* included For that, I suppose one could create a table for storing such metadata, or abuse COMMENT. It'd also be nice to be able to specify the ability to exclude specified objects entirely - I'm thinking of 3rd party modules (tsearch2, say) that one would want to install by hand (to get the latest version or whatever). I recently got a script to do something similar for MySQL by parsing the output of 'show create table'. It's pretty simple & not full-featured. I need to check with the author before posting it though. If anyone is inclined to work on this, I might be able to route a few dollars their way... please contact me off list. -- Peter Fein pfein@pobox.com 773-575-0694 Basically, if you're not a utopianist, you're a schmuck. -J. Feldman
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