Simon Riggs wrote:
> pg_dump restore times can be high when they include many ALTER TABLE ADD
> FORIEGN KEY statements, since each statement checks the data to see if
> it is fully valid in all cases.
>
> I've been asked "why we run that at all?", since if we dumped the tables
> together, we already know they match.
>
> If we had a way of pg_dump passing on the information that the test
> already passes, we would be able to skip the checks.
>
> Proposal:
>
> * Introduce a new mode for ALTER TABLE ADD FOREIGN KEY [WITHOUT CHECK];
> When we run WITHOUT CHECK, iff both the source and target table are
> newly created in this transaction, then we skip the check. If the check
> is skipped we mark the constraint as being unchecked, so we can tell
> later if this has been used.
>
> * Have pg_dump write the new syntax into its dumps, when both the source
> and target table are dumped in same run
>
> I'm guessing that the WITHOUT CHECK option would not be acceptable as an
> unprotected trap for our lazy and wicked users. :-)
>
This whole proposal would be a major footgun which would definitely be
abused, IMNSHO.
I think Heikki's idea of speeding up the check using a hash table of the
foreign keys possibly has merit.
cheers
andrew