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+<!-- doc/src/sgml/event-trigger.sgml -->
+
+ <chapter id="event-triggers">
+ <title>Event Triggers</title>
+
+ <indexterm zone="event-triggers">
+ <primary>event trigger</primary>
+ </indexterm>
+
+ <para>
+ To supplement the trigger mechanism discussed in <xref linkend="triggers"/>,
+ <productname>PostgreSQL</productname> also provides event triggers. Unlike regular
+ triggers, which are attached to a single table and capture only DML events,
+ event triggers are global to a particular database and are capable of
+ capturing DDL events.
+ </para>
+
+ <para>
+ Like regular triggers, event triggers can be written in any procedural
+ language that includes event trigger support, or in C, but not in plain
+ SQL.
+ </para>
+
+ <sect1 id="event-trigger-definition">
+ <title>Overview of Event Trigger Behavior</title>
+
+ <para>
+ An event trigger fires whenever the event with which it is associated
+ occurs in the database in which it is defined. Currently, the only
+ supported events are
+ <literal>ddl_command_start</literal>,
+ <literal>ddl_command_end</literal>,
+ <literal>table_rewrite</literal>
+ and <literal>sql_drop</literal>.
+ Support for additional events may be added in future releases.
+ </para>
+
+ <para>
+ The <literal>ddl_command_start</literal> event occurs just before the
+ execution of a <literal>CREATE</literal>, <literal>ALTER</literal>, <literal>DROP</literal>,
+ <literal>SECURITY LABEL</literal>,
+ <literal>COMMENT</literal>, <literal>GRANT</literal> or <literal>REVOKE</literal>
+ command. No check whether the affected object exists or doesn't exist is
+ performed before the event trigger fires.
+ As an exception, however, this event does not occur for
+ DDL commands targeting shared objects &mdash; databases, roles, and tablespaces
+ &mdash; or for commands targeting event triggers themselves. The event trigger
+ mechanism does not support these object types.
+ <literal>ddl_command_start</literal> also occurs just before the execution of a
+ <literal>SELECT INTO</literal> command, since this is equivalent to
+ <literal>CREATE TABLE AS</literal>.
+ </para>
+
+ <para>
+ The <literal>ddl_command_end</literal> event occurs just after the execution of
+ this same set of commands. To obtain more details on the <acronym>DDL</acronym>
+ operations that took place, use the set-returning function
+ <literal>pg_event_trigger_ddl_commands()</literal> from the
+ <literal>ddl_command_end</literal> event trigger code (see
+ <xref linkend="functions-event-triggers"/>). Note that the trigger fires
+ after the actions have taken place (but before the transaction commits),
+ and thus the system catalogs can be read as already changed.
+ </para>
+
+ <para>
+ The <literal>sql_drop</literal> event occurs just before the
+ <literal>ddl_command_end</literal> event trigger for any operation that drops
+ database objects. To list the objects that have been dropped, use the
+ set-returning function <literal>pg_event_trigger_dropped_objects()</literal> from the
+ <literal>sql_drop</literal> event trigger code (see
+ <xref linkend="functions-event-triggers"/>). Note that
+ the trigger is executed after the objects have been deleted from the
+ system catalogs, so it's not possible to look them up anymore.
+ </para>
+
+ <para>
+ The <literal>table_rewrite</literal> event occurs just before a table is
+ rewritten by some actions of the commands <literal>ALTER TABLE</literal> and
+ <literal>ALTER TYPE</literal>. While other
+ control statements are available to rewrite a table,
+ like <literal>CLUSTER</literal> and <literal>VACUUM</literal>,
+ the <literal>table_rewrite</literal> event is not triggered by them.
+ </para>
+
+ <para>
+ Event triggers (like other functions) cannot be executed in an aborted
+ transaction. Thus, if a DDL command fails with an error, any associated
+ <literal>ddl_command_end</literal> triggers will not be executed. Conversely,
+ if a <literal>ddl_command_start</literal> trigger fails with an error, no
+ further event triggers will fire, and no attempt will be made to execute
+ the command itself. Similarly, if a <literal>ddl_command_end</literal> trigger
+ fails with an error, the effects of the DDL statement will be rolled
+ back, just as they would be in any other case where the containing
+ transaction aborts.
+ </para>
+
+ <para>
+ For a complete list of commands supported by the event trigger mechanism,
+ see <xref linkend="event-trigger-matrix"/>.
+ </para>
+
+ <para>
+ Event triggers are created using the command <xref linkend="sql-createeventtrigger"/>.
+ In order to create an event trigger, you must first create a function with
+ the special return type <literal>event_trigger</literal>. This function
+ need not (and may not) return a value; the return type serves merely as
+ a signal that the function is to be invoked as an event trigger.
+ </para>
+
+ <para>
+ If more than one event trigger is defined for a particular event, they will
+ fire in alphabetical order by trigger name.
+ </para>
+
+ <para>
+ A trigger definition can also specify a <literal>WHEN</literal>
+ condition so that, for example, a <literal>ddl_command_start</literal>
+ trigger can be fired only for particular commands which the user wishes
+ to intercept. A common use of such triggers is to restrict the range of
+ DDL operations which users may perform.
+ </para>
+ </sect1>
+
+ <sect1 id="event-trigger-matrix">
+ <title>Event Trigger Firing Matrix</title>
+
+ <para>
+ <xref linkend="event-trigger-by-command-tag"/> lists all commands
+ for which event triggers are supported.
+ </para>
+
+ <table id="event-trigger-by-command-tag">
+ <title>Event Trigger Support by Command Tag</title>
+ <tgroup cols="6">
+ <thead>
+ <row>
+ <entry>Command Tag</entry>
+ <entry><literal>ddl_command_start</literal></entry>
+ <entry><literal>ddl_command_end</literal></entry>
+ <entry><literal>sql_drop</literal></entry>
+ <entry><literal>table_rewrite</literal></entry>
+ <entry>Notes</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry align="left"><literal>ALTER AGGREGATE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER COLLATION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER CONVERSION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER DOMAIN</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER DEFAULT PRIVILEGES</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER EXTENSION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER FOREIGN DATA WRAPPER</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER FOREIGN TABLE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER FUNCTION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER LANGUAGE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER LARGE OBJECT</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER MATERIALIZED VIEW</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER OPERATOR</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER OPERATOR CLASS</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER OPERATOR FAMILY</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER POLICY</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER PROCEDURE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER PUBLICATION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER SCHEMA</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER SEQUENCE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER SERVER</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER STATISTICS</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER SUBSCRIPTION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER TABLE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER TEXT SEARCH CONFIGURATION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER TEXT SEARCH DICTIONARY</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER TEXT SEARCH PARSER</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER TEXT SEARCH TEMPLATE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER TRIGGER</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER TYPE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER USER MAPPING</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>ALTER VIEW</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>COMMENT</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center">Only for local objects</entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE ACCESS METHOD</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE AGGREGATE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE CAST</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE COLLATION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE CONVERSION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE DOMAIN</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE EXTENSION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE FOREIGN DATA WRAPPER</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE FOREIGN TABLE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE FUNCTION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE INDEX</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE LANGUAGE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE MATERIALIZED VIEW</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE OPERATOR</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE OPERATOR CLASS</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE OPERATOR FAMILY</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE POLICY</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE PROCEDURE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE PUBLICATION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE RULE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE SCHEMA</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE SEQUENCE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE SERVER</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE STATISTICS</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE SUBSCRIPTION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE TABLE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE TABLE AS</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE TEXT SEARCH CONFIGURATION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE TEXT SEARCH DICTIONARY</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE TEXT SEARCH PARSER</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE TEXT SEARCH TEMPLATE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE TRIGGER</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE TYPE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE USER MAPPING</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>CREATE VIEW</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP ACCESS METHOD</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP AGGREGATE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP CAST</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP COLLATION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP CONVERSION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP DOMAIN</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP EXTENSION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP FOREIGN DATA WRAPPER</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP FOREIGN TABLE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP FUNCTION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP INDEX</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP LANGUAGE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP MATERIALIZED VIEW</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP OPERATOR</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP OPERATOR CLASS</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP OPERATOR FAMILY</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP OWNED</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP POLICY</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP PROCEDURE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP PUBLICATION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP RULE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP SCHEMA</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP SEQUENCE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP SERVER</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP STATISTICS</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP SUBSCRIPTION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP TABLE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP TEXT SEARCH CONFIGURATION</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP TEXT SEARCH DICTIONARY</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP TEXT SEARCH PARSER</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP TEXT SEARCH TEMPLATE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP TRIGGER</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP TYPE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP USER MAPPING</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>DROP VIEW</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>GRANT</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center">Only for local objects</entry>
+ </row>
+ <row>
+ <entry align="left"><literal>IMPORT FOREIGN SCHEMA</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>REFRESH MATERIALIZED VIEW</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ <row>
+ <entry align="left"><literal>REVOKE</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center">Only for local objects</entry>
+ </row>
+ <row>
+ <entry align="left"><literal>SECURITY LABEL</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center">Only for local objects</entry>
+ </row>
+ <row>
+ <entry align="left"><literal>SELECT INTO</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>X</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"><literal>-</literal></entry>
+ <entry align="center"></entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+ </sect1>
+
+ <sect1 id="event-trigger-interface">
+ <title>Writing Event Trigger Functions in C</title>
+
+ <indexterm zone="event-trigger-interface">
+ <primary>event trigger</primary>
+ <secondary>in C</secondary>
+ </indexterm>
+
+ <para>
+ This section describes the low-level details of the interface to an
+ event trigger function. This information is only needed when writing
+ event trigger functions in C. If you are using a higher-level language
+ then these details are handled for you. In most cases you should
+ consider using a procedural language before writing your event triggers
+ in C. The documentation of each procedural language explains how to
+ write an event trigger in that language.
+ </para>
+
+ <para>
+ Event trigger functions must use the <quote>version 1</quote> function
+ manager interface.
+ </para>
+
+ <para>
+ When a function is called by the event trigger manager, it is not passed
+ any normal arguments, but it is passed a <quote>context</quote> pointer
+ pointing to a <structname>EventTriggerData</structname> structure. C functions can
+ check whether they were called from the event trigger manager or not by
+ executing the macro:
+<programlisting>
+CALLED_AS_EVENT_TRIGGER(fcinfo)
+</programlisting>
+ which expands to:
+<programlisting>
+((fcinfo)-&gt;context != NULL &amp;&amp; IsA((fcinfo)-&gt;context, EventTriggerData))
+</programlisting>
+ If this returns true, then it is safe to cast
+ <literal>fcinfo-&gt;context</literal> to type <literal>EventTriggerData
+ *</literal> and make use of the pointed-to
+ <structname>EventTriggerData</structname> structure. The function must
+ <emphasis>not</emphasis> alter the <structname>EventTriggerData</structname>
+ structure or any of the data it points to.
+ </para>
+
+ <para>
+ <structname>struct EventTriggerData</structname> is defined in
+ <filename>commands/event_trigger.h</filename>:
+
+<programlisting>
+typedef struct EventTriggerData
+{
+ NodeTag type;
+ const char *event; /* event name */
+ Node *parsetree; /* parse tree */
+ const char *tag; /* command tag */
+} EventTriggerData;
+</programlisting>
+
+ where the members are defined as follows:
+
+ <variablelist>
+ <varlistentry>
+ <term><structfield>type</structfield></term>
+ <listitem>
+ <para>
+ Always <literal>T_EventTriggerData</literal>.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><structfield>event</structfield></term>
+ <listitem>
+ <para>
+ Describes the event for which the function is called, one of
+ <literal>"ddl_command_start"</literal>, <literal>"ddl_command_end"</literal>,
+ <literal>"sql_drop"</literal>, <literal>"table_rewrite"</literal>.
+ See <xref linkend="event-trigger-definition"/> for the meaning of these
+ events.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><structfield>parsetree</structfield></term>
+ <listitem>
+ <para>
+ A pointer to the parse tree of the command. Check the PostgreSQL
+ source code for details. The parse tree structure is subject to change
+ without notice.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><structfield>tag</structfield></term>
+ <listitem>
+ <para>
+ The command tag associated with the event for which the event trigger
+ is run, for example <literal>"CREATE FUNCTION"</literal>.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </para>
+
+ <para>
+ An event trigger function must return a <symbol>NULL</symbol> pointer
+ (<emphasis>not</emphasis> an SQL null value, that is, do not
+ set <parameter>isNull</parameter> true).
+ </para>
+ </sect1>
+
+ <sect1 id="event-trigger-example">
+ <title>A Complete Event Trigger Example</title>
+
+ <para>
+ Here is a very simple example of an event trigger function written in C.
+ (Examples of triggers written in procedural languages can be found in
+ the documentation of the procedural languages.)
+ </para>
+
+ <para>
+ The function <function>noddl</function> raises an exception each time it is called.
+ The event trigger definition associated the function with
+ the <literal>ddl_command_start</literal> event. The effect is that all DDL
+ commands (with the exceptions mentioned
+ in <xref linkend="event-trigger-definition"/>) are prevented from running.
+ </para>
+
+ <para>
+ This is the source code of the trigger function:
+<programlisting><![CDATA[
+#include "postgres.h"
+#include "commands/event_trigger.h"
+
+
+PG_MODULE_MAGIC;
+
+PG_FUNCTION_INFO_V1(noddl);
+
+Datum
+noddl(PG_FUNCTION_ARGS)
+{
+ EventTriggerData *trigdata;
+
+ if (!CALLED_AS_EVENT_TRIGGER(fcinfo)) /* internal error */
+ elog(ERROR, "not fired by event trigger manager");
+
+ trigdata = (EventTriggerData *) fcinfo->context;
+
+ ereport(ERROR,
+ (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+ errmsg("command \"%s\" denied", trigdata->tag)));
+
+ PG_RETURN_NULL();
+}
+]]></programlisting>
+ </para>
+
+ <para>
+ After you have compiled the source code (see <xref linkend="dfunc"/>),
+ declare the function and the triggers:
+<programlisting>
+CREATE FUNCTION noddl() RETURNS event_trigger
+ AS 'noddl' LANGUAGE C;
+
+CREATE EVENT TRIGGER noddl ON ddl_command_start
+ EXECUTE FUNCTION noddl();
+</programlisting>
+ </para>
+
+ <para>
+ Now you can test the operation of the trigger:
+<screen>
+=# \dy
+ List of event triggers
+ Name | Event | Owner | Enabled | Function | Tags
+-------+-------------------+-------+---------+----------+------
+ noddl | ddl_command_start | dim | enabled | noddl |
+(1 row)
+
+=# CREATE TABLE foo(id serial);
+ERROR: command "CREATE TABLE" denied
+</screen>
+ </para>
+
+ <para>
+ In this situation, in order to be able to run some DDL commands when you
+ need to do so, you have to either drop the event trigger or disable it. It
+ can be convenient to disable the trigger for only the duration of a
+ transaction:
+<programlisting>
+BEGIN;
+ALTER EVENT TRIGGER noddl DISABLE;
+CREATE TABLE foo (id serial);
+ALTER EVENT TRIGGER noddl ENABLE;
+COMMIT;
+</programlisting>
+ (Recall that DDL commands on event triggers themselves are not affected by
+ event triggers.)
+ </para>
+ </sect1>
+
+ <sect1 id="event-trigger-table-rewrite-example">
+ <title>A Table Rewrite Event Trigger Example</title>
+
+ <para>
+ Thanks to the <literal>table_rewrite</literal> event, it is possible to implement
+ a table rewriting policy only allowing the rewrite in maintenance windows.
+ </para>
+
+ <para>
+ Here's an example implementing such a policy.
+<programlisting>
+CREATE OR REPLACE FUNCTION no_rewrite()
+ RETURNS event_trigger
+ LANGUAGE plpgsql AS
+$$
+---
+--- Implement local Table Rewriting policy:
+--- public.foo is not allowed rewriting, ever
+--- other tables are only allowed rewriting between 1am and 6am
+--- unless they have more than 100 blocks
+---
+DECLARE
+ table_oid oid := pg_event_trigger_table_rewrite_oid();
+ current_hour integer := extract('hour' from current_time);
+ pages integer;
+ max_pages integer := 100;
+BEGIN
+ IF pg_event_trigger_table_rewrite_oid() = 'public.foo'::regclass
+ THEN
+ RAISE EXCEPTION 'you''re not allowed to rewrite the table %',
+ table_oid::regclass;
+ END IF;
+
+ SELECT INTO pages relpages FROM pg_class WHERE oid = table_oid;
+ IF pages > max_pages
+ THEN
+ RAISE EXCEPTION 'rewrites only allowed for table with less than % pages',
+ max_pages;
+ END IF;
+
+ IF current_hour NOT BETWEEN 1 AND 6
+ THEN
+ RAISE EXCEPTION 'rewrites only allowed between 1am and 6am';
+ END IF;
+END;
+$$;
+
+CREATE EVENT TRIGGER no_rewrite_allowed
+ ON table_rewrite
+ EXECUTE FUNCTION no_rewrite();
+</programlisting>
+ </para>
+ </sect1>
+</chapter>