Re: Interconnected views

On Fri, Jun 2, 2023 at 9:36 AM Oliver Kohll <oliver(at)agilebase(dot)co(dot)uk> wrote:

> Hi,
>
> Just wondering, does anyone else create apps which might not have 'big'
> data, but quite complex arrangements of views joining to each other?
>
> If so, do you have scripts to aid refactoring them e.g. drop/recreate/test
> them in the right order etc.?
>
> I'm really impressed with the way Postgres handles these multi-layered
> views. Some of our explain analyze outputs could fill a book each! Tools
> like Depesz' can be very useful. Sometimes a little tweaking or a judicious
> index is necessary, but the performance is very reliable and scalable.
>
> Blog post about it here:
> https://blog.agilebase.co.uk/2023/05/21/refactoring-sql-views/
>
> Oliver
>

Oliver,
I built a couple of such scripts to chase down dependency trees on
views. Based on a Cybertec (Laurenz Albe) article.
https://www.cybertec-postgresql.com/en/tracking-view-dependencies-in-postgresql/

Basically, I hunted down the dependent views (we have a rich hierarchy of
views). Not like yours, maybe 10-15 deep.
But it also impacts us on Column changes...

Anyways, I generate the DROP commands, inside of a single transaction, in
the right order.
Then I apply the CREATE VIEW ... in the reverse order of the drops.
Then I commit the transaction.

I was hours away from implementing something that grabbed the view
definitions, and dropped and recreated.
But that was only useful for the column type changes, and by the time I was
there, we were pretty much done changing them.

I find it a nice feature that I can drop views within a transaction, then
recreate them, in the same transaction.
So that nothing breaks. But we have not tested this under an
"realistically heavy load".

HTH