Date: Mon, 16 Jul 2018 16:14:09 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Andrew Dunstan <andrew.dunstan@2ndquadrant.com>,
	Michael Paquier <michael@paquier.xyz>, pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] WAL logging problem in 9.4.3?
Message-ID: <20180716201409.2qfcneo4qkdwjvpv@alvherre.pgsql>
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On 2018-Jul-12, Heikki Linnakangas wrote:

> > > Thanks for the pointer.  My tap test has been covering two out of
> > > the three scenarios you have in your script.  I have been able to
> > > convert the extra as the attached, and I have added as well an
> > > extra test with TRUNCATE triggers.  So it seems to me that we want
> > > to disable the optimization if any type of trigger are defined on
> > > the relation copied to as it could be possible that these triggers
> > > work on the blocks copied as well, for any BEFORE/AFTER and
> > > STATEMENT/ROW triggers.  What do you think?
> > 
> > Yeah, this seems like the only sane approach.
> 
> Doesn't have to be a trigger, could be a CHECK constraint, datatype
> input function, etc. Admittedly, having a datatype input function that
> inserts to the table is worth a "huh?", but I'm feeling very confident
> that we can catch all such cases, and some of them might even be
> sensible.

A counterexample could be a a JSON compresion scheme that uses a catalog
for a dictionary of keys.  Hasn't this been described already?  Also not
completely out of the question for GIS data, I think (Not sure if
PostGIS does this already.)

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services