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/[email protected]
  https://www.postgresql.org/message-id/[email protected]
  https://www.postgresql.org/message-id/[email protected]

1 files changed, 105 insertions, 0 deletions

diff --git a/src/include/tcop/deparse_utility.h b/src/include/tcop/deparse_utility.h
new file mode 100644
index 00000000000..b6bcbeb3174
--- /dev/null
+++ b/src/include/tcop/deparse_utility.h
@@ -0,0 +1,105 @@
+/*-------------------------------------------------------------------------
+ *
+ * deparse_utility.h
+ *
+ * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/tcop/deparse_utility.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef DEPARSE_UTILITY_H
+#define DEPARSE_UTILITY_H
+
+#include "access/attnum.h"
+#include "catalog/objectaddress.h"
+#include "nodes/nodes.h"
+#include "utils/aclchk_internal.h"
+
+
+/*
+ * Support for keeping track of collected commands.
+ */
+typedef enum CollectedCommandType
+{
+	SCT_Simple,
+	SCT_AlterTable,
+	SCT_Grant,
+	SCT_AlterOpFamily,
+	SCT_AlterDefaultPrivileges,
+	SCT_CreateOpClass,
+	SCT_AlterTSConfig
+} CollectedCommandType;
+
+/*
+ * For ALTER TABLE commands, we keep a list of the subcommands therein.
+ */
+typedef struct CollectedATSubcmd
+{
+	ObjectAddress	address; /* affected column, constraint, index, ... */
+	Node		   *parsetree;
+} CollectedATSubcmd;
+
+typedef struct CollectedCommand
+{
+	CollectedCommandType type;
+	bool		in_extension;
+	Node	   *parsetree;
+
+	union
+	{
+		/* most commands */
+		struct
+		{
+			ObjectAddress address;
+			ObjectAddress secondaryObject;
+		} simple;
+
+		/* ALTER TABLE, and internal uses thereof */
+		struct
+		{
+			Oid		objectId;
+			Oid		classId;
+			List   *subcmds;
+		} alterTable;
+
+		/* GRANT / REVOKE */
+		struct
+		{
+			InternalGrant *istmt;
+		} grant;
+
+		/* ALTER OPERATOR FAMILY */
+		struct
+		{
+			ObjectAddress address;
+			List   *operators;
+			List   *procedures;
+		} opfam;
+
+		/* CREATE OPERATOR CLASS */
+		struct
+		{
+			ObjectAddress address;
+			List   *operators;
+			List   *procedures;
+		} createopc;
+
+		/* ALTER TEXT SEARCH CONFIGURATION ADD/ALTER/DROP MAPPING */
+		struct
+		{
+			ObjectAddress address;
+			Oid	   *dictIds;
+			int		ndicts;
+		} atscfg;
+
+		/* ALTER DEFAULT PRIVILEGES */
+		struct
+		{
+			GrantObjectType objtype;
+		} defprivs;
+	} d;
+} CollectedCommand;
+
+#endif	/* DEPARSE_UTILITY_H */