Horton

Re: using index or check in ALTER TABLE SET NOT NULL

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Stephen Frost <sfrost@snowman.net>
Cc: Robert Haas <robertmhaas@gmail.com>, Sergei Kornilov <sk@zsrv.org>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2017-11-29T16:15:07Z
Lists: pgsql-hackers 
Stephen Frost <sfrost@snowman.net> writes:
> * Tom Lane (tgl@sss.pgh.pa.us) wrote:
>> I did not look at the patch yet, but TBH if it uses SPI for sub-operations
>> of ALTER TABLE I think that is sufficient reason to reject it out of hand.

> You mean like what ALTER TABLE ... ADD FOREIGN KEY does?

Yeah, and if you look at the warts that SPI has grown to support that
usage, you'll see why I'm so unhappy.  We should never have allowed
FKs to be built on top of SPI; they require semantics that don't exist
in SQL.  I think this would lead to more of the same --- not exactly
the same of course, but more warts.  See Robert's nearby musings about
semantics of index null checks for an example.

			regards, tom lane

Commits

  1. Avoid using INFO elevel for what are fundamentally debug messages.

  2. Revert setting client_min_messages to 'debug1' in new tests.

  3. Allow ALTER TABLE .. SET NOT NULL to skip provably unnecessary scans.

  4. Improve predtest.c's internal docs, and enhance its functionality a bit.