Hi Laurenz! On 2 Dec 2013, at 19:27, Albe Laurenz <laurenz.a...@wien.gv.at> wrote: > What strikes me is that since foreign key constraints are implemented > as triggers in PostgreSQL, this solution would probably not have many > performance benefits over a self-written trigger that implements the > same functionality. Since you need two triggers for your example, > the performance might even be worse than a single self-written trigger.
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Well, the main cost on insert in the FK table should be looking for matching rows in the referenced tables, which the patch avoids for non-matching rows. So while you’ll get the overhead of N triggers firing, you only pay the expected query cost (which will even use a partial index if you’ve got one set up). Each of the referenced tables is only involved in one FK, so there’s no difference in cost there. > Now performance isn't everything, but that would mean that the benefit > of your proposal is entirely on the usability side. Well, I don’t think there’s much of a performance hit, and I don’t think any of the alternatives would perform much better in practice, but certainly performance wasn’t a motivating factor for this feature, it was a) correctness and b) avoiding the ugliness of the existing solutions. > I personally don't think that it is so difficult to write a trigger > for that functionality yourself, but I guess that the argument for > this feature rests on how coveted such a functionality would be > (to justify the trade-off in code complexity). The patch is pretty small so far - and more than half of it is regression tests. So there’s not much extra code complexity IMO. I wouldn’t want to touch the FK system with anything but the lightest touch. Cheers Tom -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
