From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@2ndquadrant.com>
cc: Dimitri Fontaine <dimitri@2ndQuadrant.fr>,
	Simon Riggs <simon@2ndquadrant.com>, Robert Haas <robertmhaas@gmail.com>,
	Alvaro Herrera <alvherre@2ndquadrant.com>,
	PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Subject: Re: Event Triggers: adding information
In-reply-to: <20130118030124.GI3074@awork2.anarazel.de>
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Comments: In-reply-to Andres Freund <andres@2ndquadrant.com>
	message dated "Fri, 18 Jan 2013 04:01:25 +0100"
Date: Thu, 17 Jan 2013 22:14:04 -0500
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Andres Freund <andres@2ndquadrant.com> writes:
> On 2013-01-17 21:48:01 -0500, Tom Lane wrote:
>> If we're only interested in replication, let's put in some hooks whose
>> contract does not allow for side-effects on the local catalogs, and be
>> done.  Otherwise we'll be putting in man-years of unnecessary (or at
>> least unnecessary for this use-case) work.

> Its a thing of perspective I guess. I can't imagine a hook-ey solution,
> without quite a bit of work, that gets enough information to regenerate
> SQL that performs the same action on another system. ISTM that the
> refactoring to make that consistently "easy" is the hard part, but I
> hope I am wrong.

The problem of how to get the information needed is real and large,
I agree.  But that's not any easier for a trigger --- if anything,
it's probably harder, because then you not only need to *get* the
information but you have to figure out how to provide it in a way
that makes sense at SQL level.

			regards, tom lane


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