Re: Command Triggers, patch v11

On 9 March 2012 15:05, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> On Fri, Mar 9, 2012 at 9:22 AM, Thom Brown <thom@linux.com> wrote:
>>> Sorry, I meant any command trigger.  It's because none of the commands
>>> can be run on a standby, so the triggers don't seem appropriate.
>
>> I'm not convinced.  Right now, it's fairly useless - all the triggers
>> could possibly do is throw an error, and an error is going to get
>> thrown anyway, so it's only a question of which error message the user
>> will see.  But we discussed before the idea of adding a capability for
>> BEFORE triggers to request that the actual execution of the command
>> get skipped, and then it's possible to imagine this being useful.
>
> Um, surely the "you can't do that in a read-only session" error is going
> to get thrown long before the command trigger could be called?

Yes, at the moment that's the case.  I said that this wasn't the case
for utility commands but I've noticed the message is different for
those:

ERROR:  cannot execute VACUUM during recovery

vs

ERROR:  cannot execute CREATE TABLE in a read-only transaction

So my complaint around that was misleading and wrong.

--
Thom