Allow on-the-fly capture of DDL event details

This feature lets user code inspect and take action on DDL events.
Whenever a ddl_command_end event trigger is installed, DDL actions
executed are saved to a list which can be inspected during execution of
a function attached to ddl_command_end.

The set-returning function pg_event_trigger_ddl_commands can be used to
list actions so captured; it returns data about the type of command
executed, as well as the affected object.  This is sufficient for many
uses of this feature.  For the cases where it is not, we also provide a
"command" column of a new pseudo-type pg_ddl_command, which is a
pointer to a C structure that can be accessed by C code.  The struct
contains all the info necessary to completely inspect and even
reconstruct the executed command.

There is no actual deparse code here; that's expected to come later.
What we have is enough infrastructure that the deparsing can be done in
an external extension.  The intention is that we will add some deparsing
code in a later release, as an in-core extension.

A new test module is included.  It's probably insufficient as is, but it
should be sufficient as a starting point for a more complete and
future-proof approach.

Authors: Álvaro Herrera, with some help from Andres Freund, Ian Barwick,
Abhijit Menon-Sen.

Reviews by Andres Freund, Robert Haas, Amit Kapila, Michael Paquier,
Craig Ringer, David Steele.
Additional input from Chris Browne, Dimitri Fontaine, Stephen Frost,
Petr Jelínek, Tom Lane, Jim Nasby, Steven Singer, Pavel Stěhule.

Based on original work by Dimitri Fontaine, though I didn't use his
code.

Discussion:
  https://www.postgresql.org/message-id/m2txrsdzxa.fsf@2ndQuadrant.fr
  https://www.postgresql.org/message-id/20131108153322.GU5809@eldon.alvh.no-ip.org
  https://www.postgresql.org/message-id/20150215044814.GL3391@alvh.no-ip.org

1 files changed, 30 insertions, 33 deletions

diff --git a/src/backend/commands/opclasscmds.c b/src/backend/commands/opclasscmds.c
index c327cc0473e..3375f10861d 100644
--- a/src/backend/commands/opclasscmds.c
+++ b/src/backend/commands/opclasscmds.c
@@ -25,6 +25,7 @@
 #include "catalog/dependency.h"
 #include "catalog/indexing.h"
 #include "catalog/objectaccess.h"
+#include "catalog/opfam_internal.h"
 #include "catalog/pg_amop.h"
 #include "catalog/pg_amproc.h"
 #include "catalog/pg_namespace.h"
@@ -35,6 +36,7 @@
 #include "catalog/pg_type.h"
 #include "commands/alter.h"
 #include "commands/defrem.h"
+#include "commands/event_trigger.h"
 #include "miscadmin.h"
 #include "parser/parse_func.h"
 #include "parser/parse_oper.h"
@@ -47,24 +49,12 @@
 #include "utils/tqual.h"
 
 
-/*
- * We use lists of this struct type to keep track of both operators and
- * procedures while building or adding to an opfamily.
- */
-typedef struct
-{
-	Oid			object;			/* operator or support proc's OID */
-	int			number;			/* strategy or support proc number */
-	Oid			lefttype;		/* lefttype */
-	Oid			righttype;		/* righttype */
-	Oid			sortfamily;		/* ordering operator's sort opfamily, or 0 */
-} OpFamilyMember;
-
-
-static void AlterOpFamilyAdd(List *opfamilyname, Oid amoid, Oid opfamilyoid,
+static void AlterOpFamilyAdd(AlterOpFamilyStmt *stmt,
+				 Oid amoid, Oid opfamilyoid,
 				 int maxOpNumber, int maxProcNumber,
 				 List *items);
-static void AlterOpFamilyDrop(List *opfamilyname, Oid amoid, Oid opfamilyoid,
+static void AlterOpFamilyDrop(AlterOpFamilyStmt *stmt,
+				  Oid amoid, Oid opfamilyoid,
 				  int maxOpNumber, int maxProcNumber,
 				  List *items);
 static void processTypesSpec(List *args, Oid *lefttype, Oid *righttype);
@@ -675,6 +665,9 @@ DefineOpClass(CreateOpClassStmt *stmt)
 	storeProcedures(stmt->opfamilyname, amoid, opfamilyoid,
 					opclassoid, procedures, false);
 
+	/* let event triggers know what happened */
+	EventTriggerCollectCreateOpClass(stmt, opclassoid, operators, procedures);
+
 	/*
 	 * Create dependencies for the opclass proper.  Note: we do not create a
 	 * dependency link to the AM, because we don't currently support DROP
@@ -822,13 +815,11 @@ AlterOpFamily(AlterOpFamilyStmt *stmt)
 	 * ADD and DROP cases need separate code from here on down.
 	 */
 	if (stmt->isDrop)
-		AlterOpFamilyDrop(stmt->opfamilyname, amoid, opfamilyoid,
-						  maxOpNumber, maxProcNumber,
-						  stmt->items);
+		AlterOpFamilyDrop(stmt, amoid, opfamilyoid,
+						  maxOpNumber, maxProcNumber, stmt->items);
 	else
-		AlterOpFamilyAdd(stmt->opfamilyname, amoid, opfamilyoid,
-						 maxOpNumber, maxProcNumber,
-						 stmt->items);
+		AlterOpFamilyAdd(stmt, amoid, opfamilyoid,
+						 maxOpNumber, maxProcNumber, stmt->items);
 
 	return opfamilyoid;
 }
@@ -837,9 +828,8 @@ AlterOpFamily(AlterOpFamilyStmt *stmt)
  * ADD part of ALTER OP FAMILY
  */
 static void
-AlterOpFamilyAdd(List *opfamilyname, Oid amoid, Oid opfamilyoid,
-				 int maxOpNumber, int maxProcNumber,
-				 List *items)
+AlterOpFamilyAdd(AlterOpFamilyStmt *stmt, Oid amoid, Oid opfamilyoid,
+				 int maxOpNumber, int maxProcNumber, List *items)
 {
 	List	   *operators;		/* OpFamilyMember list for operators */
 	List	   *procedures;		/* OpFamilyMember list for support procs */
@@ -958,19 +948,22 @@ AlterOpFamilyAdd(List *opfamilyname, Oid amoid, Oid opfamilyoid,
 	 * Add tuples to pg_amop and pg_amproc tying in the operators and
 	 * functions.  Dependencies on them are inserted, too.
 	 */
-	storeOperators(opfamilyname, amoid, opfamilyoid,
+	storeOperators(stmt->opfamilyname, amoid, opfamilyoid,
 				   InvalidOid, operators, true);
-	storeProcedures(opfamilyname, amoid, opfamilyoid,
+	storeProcedures(stmt->opfamilyname, amoid, opfamilyoid,
 					InvalidOid, procedures, true);
+
+	/* make information available to event triggers */
+	EventTriggerCollectAlterOpFam(stmt, opfamilyoid,
+								  operators, procedures);
 }
 
 /*
  * DROP part of ALTER OP FAMILY
  */
 static void
-AlterOpFamilyDrop(List *opfamilyname, Oid amoid, Oid opfamilyoid,
-				  int maxOpNumber, int maxProcNumber,
-				  List *items)
+AlterOpFamilyDrop(AlterOpFamilyStmt *stmt, Oid amoid, Oid opfamilyoid,
+				  int maxOpNumber, int maxProcNumber, List *items)
 {
 	List	   *operators;		/* OpFamilyMember list for operators */
 	List	   *procedures;		/* OpFamilyMember list for support procs */
@@ -1033,8 +1026,12 @@ AlterOpFamilyDrop(List *opfamilyname, Oid amoid, Oid opfamilyoid,
 	/*
 	 * Remove tuples from pg_amop and pg_amproc.
 	 */
-	dropOperators(opfamilyname, amoid, opfamilyoid, operators);
-	dropProcedures(opfamilyname, amoid, opfamilyoid, procedures);
+	dropOperators(stmt->opfamilyname, amoid, opfamilyoid, operators);
+	dropProcedures(stmt->opfamilyname, amoid, opfamilyoid, procedures);
+
+	/* make information available to event triggers */
+	EventTriggerCollectAlterOpFam(stmt, opfamilyoid,
+								  operators, procedures);
 }
 
 
@@ -1673,7 +1670,7 @@ RemoveAmProcEntryById(Oid entryOid)
 	heap_close(rel, RowExclusiveLock);
 }
 
-static char *
+char *
 get_am_name(Oid amOid)
 {
 	HeapTuple	tup;