doc: Add better description for rewrite functions in event triggers

There are two functions that can be used in event triggers to get more
details about a rewrite happening on a relation.  Both had a limited
documentation:
- pg_event_trigger_table_rewrite_reason() and
pg_event_trigger_table_rewrite_oid() were not mentioned in the main
event trigger section in the paragraph dedicated to the event
table_rewrite.
- pg_event_trigger_table_rewrite_reason() returns an integer which is a
bitmap of the reasons why a rewrite happens.  There was no explanation
about the meaning of these values, forcing the reader to look at the
code to find out that these are defined in event_trigger.h.

While on it, let's add a comment in event_trigger.h where the
AT_REWRITE_* are defined, telling to update the documentation when
these values are changed.

Backpatch down to 13 as a consequence of 1ad23335f36b, where this area
of the documentation has been heavily reworked.

Author: Greg Sabino Mullane
Discussion: https://postgr.es/m/CAKAnmmL+Z6j-C8dAx1tVrnBmZJu+BSoc68WSg3sR+CVNjBCqbw@mail.gmail.com
Backpatch-through: 13

diff --git a/doc/src/sgml/event-trigger.sgml b/doc/src/sgml/event-trigger.sgml
index 3b6a5361b3459228432326ce517ba99cd0197fad..ff369bed19fe75090469892d1012defb5886347d 100644 (file)
--- a/doc/src/sgml/event-trigger.sgml
+++ b/doc/src/sgml/event-trigger.sgml
@@ -80,6 +80,11 @@
     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.
+    To find the OID of the table that was rewritten, use the function
+    <literal>pg_event_trigger_table_rewrite_oid()</literal> (see
+    <xref linkend="functions-event-triggers"/>). To discover the reason(s)
+    for the rewrite, use the function
+    <literal>pg_event_trigger_table_rewrite_reason()</literal>.
    </para>
 
    <para>

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 847fee1684fd7f3089d192ce77a6f40a2fc2d621..51fcfc26c919f3676e165e703aa1df1fcaa0829f 100644 (file)
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -29206,8 +29206,12 @@ CREATE EVENT TRIGGER test_event_trigger_for_drops
         <returnvalue>integer</returnvalue>
        </para>
        <para>
-        Returns a code explaining the reason(s) for rewriting.  The exact
-        meaning of the codes is release dependent.
+        Returns a code explaining the reason(s) for rewriting. The value is
+        a bitmap built from the following values: <literal>1</literal>
+        (the table has changed its persistence), <literal>2</literal>
+        (default value of a column has changed), <literal>4</literal>
+        (a column has a new data type) and <literal>8</literal>
+        (the table access method has changed).
        </para></entry>
       </row>
      </tbody>

diff --git a/src/include/commands/event_trigger.h b/src/include/commands/event_trigger.h
index 5ed6ece555d05e029b4c8811d485a456035a1e63..eb84a1a9dc4984ac0e0f00f3caa5d28c9a1c6c58 100644 (file)
--- a/src/include/commands/event_trigger.h
+++ b/src/include/commands/event_trigger.h
@@ -29,6 +29,12 @@ typedef struct EventTriggerData
    CommandTag  tag;
 } EventTriggerData;
 
+/*
+ * Reasons for relation rewrites.
+ *
+ * pg_event_trigger_table_rewrite_reason() uses these values, so make sure to
+ * update the documentation when changing this list.
+ */
 #define AT_REWRITE_ALTER_PERSISTENCE   0x01
 #define AT_REWRITE_DEFAULT_VAL         0x02
 #define AT_REWRITE_COLUMN_REWRITE      0x04