On 24 February 2012 22:32, Thom Brown <[email protected]> wrote:
> On 24 February 2012 22:04, Dimitri Fontaine <[email protected]> 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
<!--
doc/src/sgml/ref/alter_trigger.sgml
PostgreSQL documentation
-->
<refentry id="SQL-ALTERCOMMANDTRIGGER">
<refmeta>
<refentrytitle>ALTER COMMAND TRIGGER</refentrytitle>
<manvolnum>7</manvolnum>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
<refnamediv>
<refname>ALTER COMMAND TRIGGER</refname>
<refpurpose>change the definition of a trigger</refpurpose>
</refnamediv>
<indexterm zone="sql-altercommandtrigger">
<primary>ALTER COMMAND TRIGGER</primary>
</indexterm>
<refsynopsisdiv>
<synopsis>
ALTER COMMAND TRIGGER <replaceable class="PARAMETER">name</replaceable> ON <replaceable class="PARAMETER">command</replaceable> SET <replaceable class="parameter">enabled</replaceable>
<phrase>where <replaceable class="parameter">enabled</replaceable> can be one of:</phrase>
ENABLE
ENABLE ALWAYS
ENABLE REPLICA
DISABLE
</synopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>
<command>ALTER COMMAND TRIGGER</command> changes properties of an
existing command trigger.
</para>
<para>
You must be superuser to alter a command trigger.
</para>
</refsect1>
<refsect1>
<title>Parameters</title>
<variablelist>
<varlistentry>
<term><replaceable class="PARAMETER">name</replaceable></term>
<listitem>
<para>
The name of an existing trigger to alter.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">command</replaceable></term>
<listitem>
<para>
The command tag on which this trigger acts.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">enabled</replaceable></term>
<listitem>
<para>
When to enable this trigger. See
the <literal>session_replication_role</literal> parameter.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Compatibility</title>
<para>
<command>ALTER COMMAND TRIGGER</command> is a <productname>PostgreSQL</>
extension of the SQL standard.
</para>
</refsect1>
<refsect1>
<title>See Also</title>
<simplelist type="inline">
<member><xref linkend="sql-createcommandtrigger"></member>
<member><xref linkend="sql-dropcommandtrigger"></member>
</simplelist>
</refsect1>
</refentry>
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