Re: CASCADE/fkey order - Mailing list pgsql-general

From Michel Pelletier
Subject Re: CASCADE/fkey order
Date
Msg-id CACxu=vL57HC3nCvbUZUeOJj2_rku38xgOQ_SatJ-8_y_H4qwxg@mail.gmail.com
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In response to Re: CASCADE/fkey order  (Samuel Nelson <valczir.darkvein@gmail.com>)
List pgsql-general
You can benchmark your scenario with and without constraint using a tool like nancy:


it lets you A/B test different configurations with your own scenarios or using pgbench synthetic workloads.

-Michel

On Wed, Jul 22, 2020 at 9:27 AM Samuel Nelson <valczir.darkvein@gmail.com> wrote:
I checked, and changing the `bazinga_foo_bar` constraint to:

alter table bazinga add constraint bazinga_foo_bar foreign key (foo_id, bar_id) references foo_bar (foo_id, bar_id) deferrable initially deferred;

seems to fix it to work as we were expecting.  Is that particularly costly?  Should I only set the constraint to be deferred when we really need it?  Would it be more efficient to perform the deletes explicitly within a transaction rather than relying on the cascades and deferring that one constraint?

Our resident ex-Oracle DBA said that deferred constraints used to be heavily recommended against, but he also admitted that he hasn't kept up with that in the past 10 years.

-Sam

https://github.com/nelsam

"As an adolescent I aspired to lasting fame, I craved factual certainty, and
I thirsted for a meaningful vision of human life -- so I became a scientist.
This is like becoming an archbishop so you can meet girls."
-- Matt Cartmill


On Wed, Jul 22, 2020 at 10:31 AM David G. Johnston <david.g.johnston@gmail.com> wrote:
On Wed, Jul 22, 2020 at 8:24 AM Samuel Nelson <valczir.darkvein@gmail.com> wrote:
Is there a way to force the delete to cascade to tables in a specific order?

No really, but you can defer constraint checking.


David J.
 

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