Re: Command Triggers, patch v11

On 24 February 2012 22:32, Thom Brown <thom(at)linux(dot)com> wrote:
> On 24 February 2012 22:04, Dimitri Fontaine <dimitri(at)2ndquadrant(dot)fr> wrote:
>> Hi,
>>
>> Please find attached the latest version of the command triggers patch,
>> in context diff format, with support for 79 commands and documentation
>> about why only those, and with some limitations explained.
>>
>> I also cleaned up the node function support business that was still in
>> there from the command rewriting stuff that we dropped, and did a merge
>> from tonight's master branch (one of a few clean merges).
>>
>> This is now the whole of it, and I continue being available to make any
>> necessary change, although I expect only minor changes now.  Thanks to
>> all reviewers and participants into the previous threads, you all have
>> allowed me to reach the current point by your precious advice, comments
>> and interest.
>>
>> The patch implements :
>>
>>  - BEFORE/AFTER ANY command triggers
>>  - BEFORE/AFTER command triggers for 79 documented commands
>>  - regression tests exercised by the serial schedule only
>>  - documentation updates with examples
>>
>> That means you need to `make installcheck` here. Installing the tests in
>> the parallel schedule does not lead to consistent output as installing a
>> command trigger will impact any other test using that command, and the
>> output becomes subject to the exact ordering of the concurrent tests.
>>
>> The only way for a BEFORE command triggers to change the command's
>> behaviour is by raising an exception that aborts the whole transaction.
>>
>> Command triggers are called with the following arguments:
>>
>>  - the “event” (similar to TG_WHEN, either 'BEFORE' or 'AFTER')
>>  - the command tag (the real one even when an ANY trigger is called)
>>  - the object Id if available (e.g. NULL for a CREATE statement)
>>  - the schema name (can be NULL)
>>  - the object name (can be NULL)
>>
>> When the trigger's procedure we're calling is written in C, then another
>> argument is passed next, which is the parse tree Node * pointer.
>>
>> I've been talking with Marko Kreen about supporting ALTER TABLE and such
>> commands automatically in Londiste: given that patch, it requires
>> writing code in C that will rewrite the command string.  It so happens
>> that I already have worked on that code, so we intend on bringing
>> support for ALTER TABLE and other commands in Skytools 3 for 9.2.
>>
>> I think the support code should be made into an extension that both
>> Skytools and Slony would be able to share. The extension code will be
>> able to adapt to major versions changes as they are released.  Bucardo
>> would certainly be interested too, we could NOTIFY it from such an
>> extension.  The design is yet to be done here, but it's clearly possible
>> to implement such a feature given the current patch.
>>
>> The ANY trigger support is mainly there to allow people to stop any DDL
>> traffic on their databases, then allowing it explicitly with an ALTER
>> COMMAND TRIGGER ... SET DISABLE when appropriate only.  To that
>> end, the ANY command trigger is supporting more commands than you can
>> attach specific triggers too.
>>
>> It's also possible to ENABLE a command trigger on the REPLICA only
>> thanks to the session_replication_role GUC.  Support for command
>> triggers on an Hot Standby node is not provided in this patch.
>
> Hi Dimitri,
>
> I just tried building the docs with your patch and it appears
> doc/src/sgml/ref/allfiles.sgml hasn't been updated with the necessary
> references for alterCommandTrigger, createCommandTrigger and
> dropCommandTrigger.
>
> Also in ref/alter_command_trigger.sgml, you define SQL-CREATETRIGGER.
> Shouldn't this be SQL-CREATECOMMANDTRIGGER?  And there also appears to
> be orphaned text in the file too, such as "Forbids the execution of
> any DDL command".  And there's a stray </para> on line 299.
>
> I attach updated versions of both of those files, which seems to fix
> all these problems.

I've just noticed there's an issue with
doc/src/sgml/ref/alter_command_trigger.sgml too. It uses <indexterm
zone="sql-altertrigger"> which should be sql-altercommandtrigger. (as
attached)

--
Thom