Date: Fri, 18 Jan 2013 02:33:34 +0100
From: Andres Freund <andres@2ndquadrant.com>
To: Dimitri Fontaine <dimitri@2ndQuadrant.fr>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, 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
Message-ID: <20130118013334.GE3074@awork2.anarazel.de>
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On 2013-01-17 23:48:23 +0100, Dimitri Fontaine wrote:
> Tom Lane <tgl@sss.pgh.pa.us> writes:
> > Alternatively, if you want to get something into 9.3 that has not
> > necessarily got a long-term-stable API, I'd be inclined to suggest that
> > we forget about a SQL-level event trigger facility for now, and just put
> > in some hook call points.  It's pretty well established that we're
> > willing to change the API seen by hook functions across major releases.
>
> Or just a hook. That would want to have about the exact same amount of
> information as the Event Trigger anyway, so I'm thinking we could maybe
> do that the same way as the parsetree exposure?
>
> Another idea would be yet another GUC, ala allow_system_table_mods, so
> that only intrepid users can have at it. Well, as long as the logical
> replication use case is covered, I'm done here, so I want to hear from
> Simon and Andres on that (and maybe the Slony and Londiste guys, etc),
> and from you to triage what is possible and what is crazy.

> > TBH this might be the best thing anyway if your long-term goals have to
> > do with replication, because it'd be a lot cheaper to get to the point
> > where you could write the replication code and see if it all actually
> > works.  I'm fairly concerned that we might spend many man-months getting
> > event triggers with definitions A,B,C into the system, only to find out
> > later that what is really needed for logical replication is definitions
> > D,E,F.

I have no problem requiring C code to use the even data, be it via hooks
or via C functions called from event triggers. The problem I have with
putting in some hooks is that I doubt that you can find sensible spots
with enough information to actually recreate the DDL for a remote system
without doing most of the work for command triggers.


Greetings,

Andres Freund

--
 Andres Freund	                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services


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