Changes pg_trigger and extend pg_rewrite in order to allow triggers and

rules to be defined with different, per session controllable, behaviors
for replication purposes.

This will allow replication systems like Slony-I and, as has been stated
on pgsql-hackers, other products to control the firing mechanism of
triggers and rewrite rules without modifying the system catalog directly.

The firing mechanisms are controlled by a new superuser-only GUC
variable, session_replication_role, together with a change to
pg_trigger.tgenabled and a new column pg_rewrite.ev_enabled. Both
columns are a single char data type now (tgenabled was a bool before).
The possible values in these attributes are:

     'O' - Trigger/Rule fires when session_replication_role is "origin"
           (default) or "local". This is the default behavior.

     'D' - Trigger/Rule is disabled and fires never

     'A' - Trigger/Rule fires always regardless of the setting of
           session_replication_role

     'R' - Trigger/Rule fires when session_replication_role is "replica"

The GUC variable can only be changed as long as the system does not have
any cached query plans. This will prevent changing the session role and
accidentally executing stored procedures or functions that have plans
cached that expand to the wrong query set due to differences in the rule
firing semantics.

The SQL syntax for changing a triggers/rules firing semantics is

     ALTER TABLE <tabname> <when> TRIGGER|RULE <name>;

     <when> ::= ENABLE | ENABLE ALWAYS | ENABLE REPLICA | DISABLE

psql's \d command as well as pg_dump are extended in a backward
compatible fashion.

Jan

src/backend/utils/misc/guc.c

@@ -10,7 +10,7 @@
  * Written by Peter Eisentraut <peter_e@gmx.net>.
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.382 2007/03/13 14:32:25 petere Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.383 2007/03/19 23:38:30 wieck Exp $
  *
  *--------------------------------------------------------------------
  */
@@ -34,6 +34,7 @@
 #include "commands/async.h"
 #include "commands/vacuum.h"
 #include "commands/variable.h"
+#include "commands/trigger.h"
 #include "funcapi.h"
 #include "libpq/auth.h"
 #include "libpq/pqformat.h"
@@ -59,6 +60,7 @@
 #include "utils/guc_tables.h"
 #include "utils/memutils.h"
 #include "utils/pg_locale.h"
+#include "utils/plancache.h"
 #include "utils/ps_status.h"
 #include "utils/tzparser.h"
 #include "utils/xml.h"
@@ -124,6 +126,8 @@ static const char *assign_syslog_ident(const char *ident,
 
 static const char *assign_defaultxactisolevel(const char *newval, bool doit,
 						   GucSource source);
+static const char *assign_session_replication_role(const char *newval, bool doit,
+						   GucSource source);
 static const char *assign_log_min_messages(const char *newval, bool doit,
 						GucSource source);
 static const char *assign_client_min_messages(const char *newval,
@@ -226,6 +230,7 @@ static char *backslash_quote_string;
 static char *client_encoding_string;
 static char *datestyle_string;
 static char *default_iso_level_string;
+static char *session_replication_role_string;
 static char *locale_collate;
 static char *locale_ctype;
 static char *regex_flavor_string;
@@ -1928,6 +1933,16 @@ static struct config_string ConfigureNamesString[] =
 		"read committed", assign_defaultxactisolevel, NULL
 	},
 
+	{
+		{"session_replication_role", PGC_SUSET, CLIENT_CONN_STATEMENT,
+			gettext_noop("Sets the sessions behaviour for triggers and rewrite rules."),
+			gettext_noop("Each session can be either"
+						 " \"origin\", \"replica\" or \"local\".")
+		},
+		&session_replication_role_string,
+		"origin", assign_session_replication_role, NULL
+	},
+
 	{
 		{"dynamic_library_path", PGC_SUSET, CLIENT_CONN_OTHER,
 			gettext_noop("Sets the path for dynamically loadable modules."),
@@ -6115,6 +6130,33 @@ assign_defaultxactisolevel(const char *newval, bool doit, GucSource source)
 	return newval;
 }
 
+static const char *
+assign_session_replication_role(const char *newval, bool doit, GucSource source)
+{
+	if (HaveCachedPlans())
+		elog(ERROR, "session_replication_role cannot be changed "
+					"after prepared plans have been cached");
+
+	if (pg_strcasecmp(newval, "origin") == 0)
+	{
+		if (doit)
+			SessionReplicationRole = SESSION_REPLICATION_ROLE_ORIGIN;
+	}
+	else if (pg_strcasecmp(newval, "replica") == 0)
+	{
+		if (doit)
+			SessionReplicationRole = SESSION_REPLICATION_ROLE_REPLICA;
+	}
+	else if (pg_strcasecmp(newval, "local") == 0)
+	{
+		if (doit)
+			SessionReplicationRole = SESSION_REPLICATION_ROLE_LOCAL;
+	}
+	else
+		return NULL;
+	return newval;
+}
+
 static const char *
 assign_log_min_messages(const char *newval,
 						bool doit, GucSource source)

src/backend/utils/misc/postgresql.conf.sample

@@ -408,6 +408,7 @@
 #default_transaction_isolation = 'read committed'
 #default_transaction_read_only = off
 #statement_timeout = 0			# 0 is disabled
+#session_replication_role = "origin"
 #vacuum_freeze_min_age = 100000000
 #xmlbinary = 'base64'
 #xmloption = 'content'