Jeff Janes <jeff.janes@gmail.com> writes:
> On Sat, Nov 23, 2019 at 4:47 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Note that you pay a fairly substantial performance penalty for deferring
>> the check, which is why it isn't the default, even though the SQL spec
>> says it ought to be.
> Do you know what the worst case scenario is for the performance of
> deferring the check to the end of the statement (with deferred initially
> immediate)? Upon testing, I get a penalty of 2 to 5%, which seems pretty
> small, but I might not be testing the most adverse situation. See attached.
Hm, I would have expected more, though not factor-of-10 or anything
like that. But that's just vague recollection from when we put in
the feature. I'm not surprised if the numbers have moved since.
> The main "cost" that prevents from using DII routinely is that they can't
> receive foreign key constraints.
Yeah, that's an issue.
regards, tom lane
