Horton

Re: ALTER TABLE ADD COLUMN fast default

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Petr Jelinek <petr.jelinek@2ndquadrant.com>, Andrew Dunstan <andrew.dunstan@2ndquadrant.com>, Thomas Munro <thomas.munro@enterprisedb.com>, David Rowley <david.rowley@2ndquadrant.com>, Tom Lane <tgl@sss.pgh.pa.us>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2018-02-20T20:06:18Z
Lists: pgsql-hackers 
Hi,

On 2018-02-20 20:57:36 +0100, Tomas Vondra wrote:
> The question is how should the schema for TPC-H look like. Because if
> you just do the usual test without any ALTER TABLE ADD COLUMN, then you
> really won't get any difference at all. The fast default stuff will be
> completely "inactive".

Well, there'll still be changed behaviour due to the changed sizes of
structures and new out of line function calls. The deforming code is
quite sensitive to such changes.

I think just verifying that there's no meaningful effect with/without
the patch is good enough. As soon as there's actual new columns that
take advantage of the new functionality I think some degradation is fair
game, you got some benefit for it.

Greetings,

Andres Freund

Commits

  1. Clean up treatment of missing default and CHECK-constraint records.

  2. Fast ALTER TABLE ADD COLUMN with a non-NULL default

  3. Fix application of identity values in some cases