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.

Back 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
Back-through: 13

diff --git a/doc/src/sgml/event-trigger.sgml b/doc/src/sgml/event-trigger.sgml
index d03063903465748bf12db36c9f8c7b38b5de58df..cfa7b3d1b2db7f575296700868d5f4a6d68da681 100644 (file)
--- a/doc/src/sgml/event-trigger.sgml
+++ b/doc/src/sgml/event-trigger.sgml
@@ -104,6 +104,11 @@
     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 7be0324ac879d13e9706b8685b0fdc6ff4f83a5f..05f630c6a6c59debc9c7824dc2fbf8d46dbe975e 100644 (file)
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -31687,8 +31687,12 @@ 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 90fc1af5f696b82d3d5968f51b42f2aaeae5f22e..00cfb3975847825394ee2de53007960dd4afd08a 100644 (file)
--- a/src/include/commands/event_trigger.h
+++ b/src/include/commands/event_trigger.h
@@ -31,6 +31,12 @@ typedef struct EventTriggerData
 
 extern PGDLLIMPORT bool event_triggers;
 
+/*
+ * 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