event triggers with args?

On 2015-02-25 10:43:57 +0100, Fabien COELHO wrote:

While looking at event triggers, I noticed that, contrary to basic triggers,
arguments are not allowed.

However, the example in the documentation with an hour-based filtering of
ddl commands suggest some handling of arguments would be useful so as to
allow more generic event triggers.

So I have a question: is there a particular reason why arguments were not
provided in the first place?

Yea. The existing trigger argument mechanims is extremely odd
implementation wise - they don't have real datatypes and aren't passed
via the normal parameter passing mechanism. IIRC we discussed this back
when it was introduced and decided against introducing for now.

I think the whole trigger argument infrastructure, even for normal
triggers, should be rewritten. After that we could think of adding it
for event triggers.

Greetings,

Andres Freund

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

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Hello Andres,

So I have a question: is there a particular reason why arguments were not
provided in the first place?

Yea. The existing trigger argument mechanims is extremely odd
implementation wise - they don't have real datatypes and aren't passed
via the normal parameter passing mechanism.

Indeed, I can only agree!

IIRC we discussed this back when it was introduced and decided against
introducing for now.

I think the whole trigger argument infrastructure, even for normal
triggers, should be rewritten. After that we could think of adding it
for event triggers.

Ok. That sound reasonable. Thanks for the answer.

I think that the new method will have to be upward compatible. This
suggest providing TG_ARGV with casted to text arguments. Not necessarily a
big issue.

I've looked into the parser. ISTM that trigger call parameter list could
use a "expr_list", which would have to be evaluated and serialised in
pg_trigger, maybe as ROW does.

--
Fabien.

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