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Event Trigger for table_rewrite

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Generate a table_rewrite event when ALTER TABLE
attempts to rewrite a table. Provide helper
functions to identify table and reason.

Intended use case is to help assess or to react
to schema changes that might hold exclusive locks
for long periods.

Dimitri Fontaine, triggering an edit by Simon Riggs

Reviewed in detail by Michael Paquier
This commit is contained in:
Simon Riggs
2014-12-08 00:55:28 +09:00
parent b8e33a85d4
commit 618c9430a8
13 changed files with 556 additions and 39 deletions
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85
doc/src/sgml/func.sgml
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@@ -17607,15 +17607,23 @@ FOR EACH ROW EXECUTE PROCEDURE suppress_redundant_updates_trigger();
<sect1 id="functions-event-triggers">
<title>Event Trigger Functions</title>
<para>
<productname>PostgreSQL</> provides these helper functions
to retrieve information from event triggers.
</para>
<para>
For more information about event triggers,
see <xref linkend="event-triggers">.
</para>
<sect2 id="pg-event-trigger-sql-drop-functions">
<title>Processing objects dropped by a DDL command.</title>
<indexterm>
<primary>pg_event_trigger_dropped_objects</primary>
</indexterm>
<para>
Currently <productname>PostgreSQL</> provides one built-in event trigger
helper function, <function>pg_event_trigger_dropped_objects</>.
</para>
<para>
<function>pg_event_trigger_dropped_objects</> returns a list of all objects
dropped by the command in whose <literal>sql_drop</> event it is called.
@@ -17709,11 +17717,72 @@ CREATE EVENT TRIGGER test_event_trigger_for_drops
EXECUTE PROCEDURE test_event_trigger_for_drops();
</programlisting>
</para>
</sect2>
<para>
For more information about event triggers,
see <xref linkend="event-triggers">.
<sect2 id="pg-event-trigger-table-rewrite-functions">
<title>Handling a Table Rewrite Event</title>
<para>
The functions shown in
<xref linkend="functions-event-trigger-table-rewrite">
provide information about a table for which a
<literal>table_rewrite</> event has just been called.
If called in any other context, an error is raised.
</para>
<table id="functions-event-trigger-table-rewrite">
<title>Table Rewrite information</title>
<tgroup cols="3">
<thead>
<row><entry>Name</entry> <entry>Return Type</entry> <entry>Description</entry></row>
</thead>
<tbody>
<row>
<entry>
<indexterm><primary>pg_event_trigger_table_rewrite_oid</primary></indexterm>
<literal><function>pg_event_trigger_table_rewrite_oid()</function></literal>
</entry>
<entry><type>Oid</type></entry>
<entry>The Oid of the table about to be rewritten.</entry>
</row>
<row>
<entry>
<indexterm><primary>pg_event_trigger_table_rewrite_reason</primary></indexterm>
<literal><function>pg_event_trigger_table_rewrite_reason()</function></literal>
</entry>
<entry><type>int</type></entry>
<entry>
The reason code(s) explaining the reason for rewriting. The exact
meaning of the codes is release dependent.
</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The <function>pg_event_trigger_table_rewrite_oid</> function can be used
in an event trigger like this:
<programlisting>
CREATE FUNCTION test_event_trigger_table_rewrite_oid()
RETURNS event_trigger
LANGUAGE plpgsql AS
$$
BEGIN
RAISE NOTICE 'rewriting table % for reason %',
pg_event_trigger_table_rewrite_oid()::regclass,
pg_event_trigger_table_rewrite_reason();
END;
$$;
CREATE EVENT TRIGGER test_table_rewrite_oid
ON table_rewrite
EXECUTE PROCEDURE test_event_trigger_table_rewrite_oid();
</programlisting>
</para>
</sect2>
</sect1>
</chapter>