Re: Event Triggers: adding information

On 17 January 2013 16:15, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> As a further example, suppose that in 9.4 (or 9.17) we add a command
> "DROP TABLES IN SCHEMA fred WHERE name LIKE 'bob%'". Well, the
> logging trigger still just works (because it's only writing the
> statement, without caring about its contents). And the replication
> trigger still just works too (because it will still get a callback for
> every table that gets dropped, even though it knows nothing about the
> new syntax). That's very powerful. Of course, there will still be
> cases where things have to change, but you can minimize it by clean
> definitions.
>
> It pains me that I've evidently failed to communicate this concept
> clearly despite a year or more of trying. Does that make sense? Is
> there some way I can make this more clear? The difference seems very
> clear-cut to me, but evidently I'm not conveying it well.
>
>> That problem is going to happen in some way or another. It's not about
>> avoiding the problem completely, but choosing a set of compromises. I'm
>> yet to understand what your set of compromises is in detailed enough
>> practical implementation terms (not just "it's another set of events")
>> and how it's a better compromise over all (I trust your judgement on
>> that, I still want to understand).
>>
>> After all, the whole point of the Event Trigger patch is to expose some
>> level of implementation details.
>
> I don't really agree with that. I think the point is to expose what
> the system is doing to the DBA. I'm OK with exposing the fact that
> creating a table with a serial column also creates a sequence. There
> is no problem with that - it's all good. What we DON'T want to do is
> set up a system where the fact that it creates a sequence is exposed
> because that happens to go through ProcessUtility() and the fact that
> it creates a constraint is not because that happens not to go through
> ProcessUtility(). That is not the sort of quality that our users have
> come to expect from PostgreSQL.

"The point", i.e. the main use case, is to replicate the DDL in a useful form.

Discussions and reasoning need to focus on the main use case, not on
weird futures or qualitative points. Yes, the discussion has gone on
for years and it really should come to a useful conclusion sometime
soon.

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