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Re: mysqldiff-like utility for PG?

From: Kevin Brannen <kevinb(at)nurseamerica(dot)net>
To: pgsql-admin(at)postgresql(dot)org
Subject: Re: mysqldiff-like utility for PG?
Date: 2002-08-22 20:16:31
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-admin
Robert Treat wrote:
> On Thu, 2002-08-22 at 14:08, Kevin Brannen wrote:
>>I think you're missing the point of his request.  Upgrading applications 
>>(or anything binary) is trivial compared to upgrading a working 
>>database, IMHO.  (but maybe you just picked a bad analogy :-)
> <snip>
>>I don't see how you can keep a production DB running in any other way. 
>>If you can, please let us know!  But once a schema is being used in 
>>production, and has a data in it, you can't just drop it and stuff a new 
>>schema in; it needs to be transformed. 
> Assuming you have maintenance windows for when you would be upgrading
> your database, there's no reason you have to rule out a full drop/reload
> of the database system.

Fair enough--some people have circumstances which allow this, I don't. 
:-/   My maintanance windows are very small, and one day I will hit the 
multi-million row size, creating a physical impossibility to drop/reload 
in the time I have.  And I suspect this is not an uncommon problem. :-)

>>And that's what the diff tool 
>>does, helps to transform.
>>So he's not alone in his problem.  Hope that helps you to understand 
>>what he was asking for.
> Either method of upgrading is definitely valid under the right
> circumstances, but I would second any notion to keep entire schema
> versions in CVS and not just the "upgrades".

You bet!  I always store the entire new schema.  And I also create a 
"transition" file that contains all the sql (creates and alters) to go 
from one version to the next.  A tool to help me create this transition 
file would be a great thing! :-)

>>Hmmm, I wonder if I could write this...  Ignoring constraint changes, it 
>>doesn't sound that hard.  If I do this, I'll post it to the news group.
> I am sure there are open source projects doing something similar to this
> now (perhaps even the mentioned mysql utility?) that could give you a
> jump start. If your doing this for 7.2.2, watch out for dropping
> columns.. 

Good advice, I'll look around before I do anything.  Yeh, the lack of 
"alter table T drop column ..." is a real pain.  If I write this tool, 
I'll probably assume that command exists, which means the sql won't be 
fully valid until PG7.3. :-(


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