Skip site navigation (1) Skip section navigation (2)

Re: Command Triggers, patch v11

From: Thom Brown <thom(at)linux(dot)com>
To: Dimitri Fontaine <dimitri(at)2ndquadrant(dot)fr>
Cc: PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Command Triggers, patch v11
Date: 2012-02-25 14:30:26
Message-ID: CAA-aLv6qDiz3pdxwZwMk_ABmERSm1sOCfZ4CMiy4qVJZYb=o6g@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On 25 February 2012 13:28, Thom Brown <thom(at)linux(dot)com> wrote:
> On 25 February 2012 13:15, Thom Brown <thom(at)linux(dot)com> wrote:
>> On 25 February 2012 12:42, Thom Brown <thom(at)linux(dot)com> wrote:
>>> On 25 February 2012 12:07, Thom Brown <thom(at)linux(dot)com> wrote:
>>>> On 25 February 2012 12:00, Dimitri Fontaine <dimitri(at)2ndquadrant(dot)fr> wrote:
>>>>
>>>> D'oh, just as I sent some more queries...
>>>>
>>>>> Thom Brown <thom(at)linux(dot)com> writes:
>>>>>> Is there any reason why the list of commands that command triggers can
>>>>>> be used with isn't in alphabetical order?  Also it appears to show
>>>>>
>>>>> Any reason why?  I don't suppose it's really important one way or the
>>>>> other, so I'm waiting on some more voices before working on it.
>>>>
>>>> Just so it's easy to scan.  If someone is looking for CREATE CAST,
>>>> they'd kind of expect it near the drop of the CREATE list, but it's
>>>> actually toward the bottom.  It just looks random at the moment.
>>>>
>>>>>> The ALTER COMMAND TRIGGER page also doesn't show which commands it can
>>>>>> be used against.  Perhaps, rather than repeat the list, there could be
>>>>>> a note to say that a list of valid commands can be found on the CREATE
>>>>>> COMMAND TRIGGER page?
>>>>>
>>>>> Well you can only alter a command that you were successful in creating,
>>>>> right?  So I'm not sure that's needed here.  By that count though, I
>>>>> maybe should remove the supported command list from DROP COMMAND TRIGGER
>>>>> reference page?
>>>>
>>>> Sure, that would be more consistent.  You're right, it's not needed.
>>>> It just seemed odd that one of the statements lacked what both others
>>>> had.
>>>
>>> Yet another comment... (I should have really started looking at this
>>> at an earlier stage)
>>>
>>> It seems that if one were to enforce a naming convention for relations
>>> as shown in the 2nd example for CREATE COMMAND TRIGGER, it could be
>>> circumvented by someone using CREATE TABLE name AS...
>>>
>>> test=# CREATE TABLE badname (id int, a int, b text);
>>> ERROR:  invalid relation name: badname
>>> test=# CREATE TABLE badname AS SELECT 1::int id, 1::int a, ''::text b;
>>> SELECT 1
>>>
>>> This doesn't even get picked up by ANY COMMAND.
>>
>> CREATE COMMAND TRIGGER doesn't output in pg_dump or pg_dumpall.  I'd
>> expect ALTER COMMAND TRIGGER to output too for when individual
>> commands are disabled etc.
>
> Just found another case where a table can be created without a command
> trigger firing:
>
> SELECT * INTO badname FROM goodname;

Right, hopefully this should be my last piece of list spam for the
time being. (apologies, I thought I'd just try it out at first, but
it's ended up being reviewed piecemeal)

On CREATE COMMAND TRIGGER page:

“The trigger will be associated with the specified command and will
execute the specified function function_name when that command is
run.”
should be:
“The trigger will be associated with the specified commands and will
execute the specified function function_name when those commands are
run.”

“A command trigger's function must return void, the only it can aborts
the execution of the command is by raising an exception.”
should be:
“A command trigger's function must return void.  It can then only
abort the execution of the command by raising an exception.”

Remove:
“For a constraint trigger, this is also the name to use when modifying
the trigger's behavior using SET CONSTRAINTS.”

Remove:
“That leaves out the following list of non supported commands.”

s/exercize/exercise/

“that's the case for VACUUM, CLUSTER CREATE INDEX CONCURRENTLY, and
REINDEX DATABASE.”
should be:
“that's the case for VACUUM, CLUSTER, CREATE INDEX CONCURRENTLY, and
REINDEX DATABASE.”

I don’t understand this sentence:
“Triggers on ANY command support more commands than just this list,
and will only provide the command tag argument as NOT NULL.”


On ALTER COMMAND TRIGGER page:

“ALTER COMMAND TRIGGER name ON command SET enabled”
should be:
“ALTER COMMAND TRIGGER name ON command [, ... ] SET enabled”


On DROP COMMAND TRIGGER page:

There’s a mention of CASCADE and RESTRICT.  I don’t know of any object
which could be dependant on a command trigger, so I don’t see what
these are for.


An oddity I’ve noticed is that you can add additional commands to an
existing command trigger, and you can also have them execute a
different function to the other commands referenced in the same
trigger.

-- 
Thom

In response to

Responses

pgsql-hackers by date

Next:From: Magnus HaganderDate: 2012-02-25 14:33:11
Subject: Re: pgstat documentation tables
Previous:From: Thom BrownDate: 2012-02-25 13:28:15
Subject: Re: Command Triggers, patch v11

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group