This commit adds GUC parameter xc_maintenance_mode. This is needed to control

behavior of some statements to be used to maintain XC database integrity by
dedicate utility programs such as pgxc_clean, which is now under the
development.

Also, this patch modifies implicit 2PC xid to _$XC$%u where %u is the transactionId.
Because it is essential to distinguish implicit 2PC from explicit one to maintain
database consisitensy, this patch checks xid in PREPARE TRANSACTION and rejects
xid for implicit 2PC.

See documentation for details.

11 files changed, 166 insertions, 2 deletions

diff --git a/doc-xc/src/sgml/config.sgmlin b/doc-xc/src/sgml/config.sgmlin
index 23bf4a3385..bf6b738548 100644
--- a/doc-xc/src/sgml/config.sgmlin
+++ b/doc-xc/src/sgml/config.sgmlin
@@ -6932,6 +6932,21 @@ LOG:  CleanUpLock: deleting: lock(0xb7acd844) id(24688,24696,0,0,0,1)
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-xc-maintenance-ode" xreflabel="xc_maintenance_mode">
+      <term><varname>xc_maintenance_mode</varname> (<type>bool</type>)</term>
+      <indexterm>
+       <primary><varname>xc_maintenance_mode</> configuration parameter</primary>
+      </indexterm>
+      <listitem>
+       <para>
+        Specify to enter into maintenance mode.   Turning this on will change behavior of several statements.
+       </para>
+       <para>
+        This parameter can only be set by superuser with <literal>SET</literal> command.   Otherwise, the setting will be ignored.
+       </para>
+      </listitem>
+     </varlistentry>
+
     </variablelist>
 
   </sect1>
diff --git a/doc-xc/src/sgml/ref/prepare_transaction.sgmlin b/doc-xc/src/sgml/ref/prepare_transaction.sgmlin
index fca68de0ea..bf62e19741 100644
--- a/doc-xc/src/sgml/ref/prepare_transaction.sgmlin
+++ b/doc-xc/src/sgml/ref/prepare_transaction.sgmlin
@@ -130,6 +130,12 @@ PREPARE TRANSACTION <replaceable class="PARAMETER">transaction_id</replaceable>
    coordinator, <command>COMMIT PREPARED</> will be propagated to
    these nodes.
   </para>
+
+&xconly;
+  <para>
+   Transaction id beginning with <literal>_$XC$</literal> is reserved by COORDINATOR for
+   internal use.   You cannot use this form of transaction_id externaly.
+  </para>
 <!## end>
 
 &common;
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 89615ee0ec..c831660b23 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -5459,4 +5459,18 @@ IsTransactionLocalNode(bool write)
 	else
 		return false;
 }
+
+/*
+ * Check if the given xid is form implicit 2PC
+ */
+bool
+IsXidImplicit(const char *xid)
+{
+#define implicit2PC_head "_$XC$"
+	static size_t implicit2PC_head_len = strlen(implicit2PC_head);
+
+	if (strncmp(xid, implicit2PC_head, implicit2PC_head_len))
+		return false;
+	return true;
+}
 #endif
diff --git a/src/backend/pgxc/Makefile b/src/backend/pgxc/Makefile
index 14f9b968d3..312b4d330c 100644
--- a/src/backend/pgxc/Makefile
+++ b/src/backend/pgxc/Makefile
@@ -11,6 +11,6 @@ subdir = src/backend/pgxc
 top_builddir = ../../..
 include $(top_builddir)/src/Makefile.global
 
-SUBDIRS	    = locator plan pool barrier nodemgr
+SUBDIRS	    = locator plan pool barrier nodemgr xc_maintenance_mode
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/pgxc/xc_maintenance_mode/Makefile b/src/backend/pgxc/xc_maintenance_mode/Makefile
new file mode 100644
index 0000000000..940cb52ec2
--- /dev/null
+++ b/src/backend/pgxc/xc_maintenance_mode/Makefile
@@ -0,0 +1,19 @@
+#-------------------------------------------------------------------------
+#
+# Makefile--
+#    Makefile for barrier
+#
+#  Portions Copyright (c) 2010-2011 Nippon Telegraph and Telephone Corporation
+#
+# IDENTIFICATION
+#    $PostgreSQL$
+#
+#-------------------------------------------------------------------------
+
+subdir = src/backend/pgxc/xc_maintenance_mode
+top_builddir = ../../../..
+include $(top_builddir)/src/Makefile.global
+
+OBJS = xc_maintenance_mode.o
+
+include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/pgxc/xc_maintenance_mode/xc_maintenance_mode.c b/src/backend/pgxc/xc_maintenance_mode/xc_maintenance_mode.c
new file mode 100644
index 0000000000..7296b6e8d7
--- /dev/null
+++ b/src/backend/pgxc/xc_maintenance_mode/xc_maintenance_mode.c
@@ -0,0 +1,5 @@
+#include "pgxc/xc_maintenance_mode.h"
+
+bool xc_maintenance_mode;
+GucContext currentGucContext;
+
diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
index 97b75ca249..b29e2b47c8 100644
--- a/src/backend/tcop/utility.c
+++ b/src/backend/tcop/utility.c
@@ -73,6 +73,7 @@
 #include "pgxc/nodemgr.h"
 #include "pgxc/groupmgr.h"
 #include "utils/lsyscache.h"
+#include "pgxc/xc_maintenance_mode.h"
 
 static void ExecUtilityStmtOnNodes(const char *queryString, ExecNodes *nodes,
 								   bool force_autocommit, RemoteQueryExecType exec_type,
@@ -436,6 +437,18 @@ standard_ProcessUtility(Node *parsetree,
 
 					case TRANS_STMT_PREPARE:
 						PreventCommandDuringRecovery("PREPARE TRANSACTION");
+#ifdef PGXC
+						/* Add check if xid is valid */
+						if (IS_PGXC_COORDINATOR && !IsConnFromCoord() && !xc_maintenance_mode)
+						{
+							if (IsXidImplicit((const char *)stmt->gid))
+							{
+								elog(ERROR, "Invalid transaciton_id to prepare.");
+								break;
+							}
+						}
+#endif
+
 						if (!PrepareTransactionBlock(stmt->gid))
 						{
 							/* report unsuccessful commit in completionTag */
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 005fceeb99..d71aef982e 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -62,6 +62,7 @@
 #include "nodes/nodes.h"
 #include "pgxc/poolmgr.h"
 #include "pgxc/nodemgr.h"
+#include "pgxc/xc_maintenance_mode.h"
 #endif
 #include "postmaster/autovacuum.h"
 #include "postmaster/bgwriter.h"
@@ -197,6 +198,9 @@ static bool check_bonjour(bool *newval, void **extra, GucSource source);
 static bool check_ssl(bool *newval, void **extra, GucSource source);
 static bool check_stage_log_stats(bool *newval, void **extra, GucSource source);
 static bool check_log_stats(bool *newval, void **extra, GucSource source);
+#ifdef PGXC
+static bool check_pgxc_maintenance_mode(bool *newval, void **extra, GucSource source);
+#endif
 static bool check_canonical_path(char **newval, void **extra, GucSource source);
 static bool check_timezone_abbreviations(char **newval, void **extra, GucSource source);
 static void assign_timezone_abbreviations(const char *newval, void *extra);
@@ -636,6 +640,10 @@ const char *const config_group_names[] =
 	gettext_noop("Datanodes and Connection Pooling"),
 	/* GTM */
 	gettext_noop("GTM Connection"),
+	/* COORDINATORS */
+	gettext_noop("Coordinator Options"),
+	/* XC_HOUSEKEEPING_OPTIONS */
+	gettext_noop("XC Housekeeping Options"),
 #endif
 	/* help_config wants this array to be null-terminated */
 	NULL
@@ -1489,6 +1497,15 @@ static struct config_bool ConfigureNamesBool[] =
 		true,
 		NULL, NULL, NULL
 	},
+	{
+		{"xc_maintenance_mode", PGC_SUSET, XC_HOUSEKEEPING_OPTIONS,
+		    gettext_noop("Turn on XC maintenance mode."),
+		 	gettext_noop("Can set ON by SET command by superuser.")
+		},
+		&xc_maintenance_mode,
+		false,
+		check_pgxc_maintenance_mode, NULL, NULL
+	},
 #endif
 
 	{
@@ -5257,6 +5274,14 @@ set_config_option(const char *name, const char *value,
 	bool		prohibitValueChange = false;
 	bool		makeDefault;
 
+#ifdef PGXC
+	/*
+	 * Current GucContest value is needed to check if xc_maintenance_mode parameter
+	 * is specified in valid contests.   It is allowed only by SET command or
+	 * libpq connect parameters so that setting this ON is just temporary.
+	 */
+	currentGucContext = context;
+#endif
 	if (context == PGC_SIGHUP || source == PGC_S_DEFAULT)
 	{
 		/*
@@ -8587,6 +8612,55 @@ check_log_stats(bool *newval, void **extra, GucSource source)
 	return true;
 }
 
+#ifdef PGXC
+/*
+ * K.Suzuki, March, 2012.
+ *
+ * Here, only a warning will be printed to log.   Returning false will cause FATAL error and it
+ * will not be good.
+ */
+static bool
+check_pgxc_maintenance_mode(bool *newval, void **extra, GucSource source)
+{
+
+	switch(source)
+	{
+		case PGC_S_DYNAMIC_DEFAULT:
+		case PGC_S_ENV_VAR:
+		case PGC_S_ARGV:
+			GUC_check_errmsg("pgxc_maintenance_mode is not allowed here.");
+			return false;
+		case PGC_S_FILE:
+			switch (currentGucContext)
+			{
+				case PGC_SIGHUP:
+					elog(WARNING, "pgxc_maintenance_mode is not allowed in  postgresql.conf.  Set to default (false).");
+					*newval = false;
+					return true;
+				default:
+					GUC_check_errmsg("pgxc_maintenance_mode is not allowed in postgresql.conf.");
+					return false;
+			}
+			return false;	/* Should not come here */
+		case PGC_S_DATABASE:
+		case PGC_S_USER:
+		case PGC_S_DATABASE_USER:
+		case PGC_S_INTERACTIVE:
+		case PGC_S_TEST:
+			elog(WARNING, "pgxc_maintenance_mode is not allowed here.  Set to default (false).");
+			*newval = false;
+			return true;
+		case PGC_S_DEFAULT:
+		case PGC_S_CLIENT:
+		case PGC_S_SESSION:
+			return true;
+		default:
+			GUC_check_errmsg("Unknown source");
+			return false;
+	}
+}
+#endif
+
 static bool
 check_canonical_path(char **newval, void **extra, GucSource source)
 {
diff --git a/src/include/access/xact.h b/src/include/access/xact.h
index 67dbce2d9b..58c09a43e7 100644
--- a/src/include/access/xact.h
+++ b/src/include/access/xact.h
@@ -273,6 +273,7 @@ extern void ForgetTransactionNodes(void);
 extern void RegisterTransactionLocalNode(bool write);
 extern bool IsTransactionLocalNode(bool write);
 extern void ForgetTransactionLocalNode(void);
+extern bool IsXidImplicit(const char *xid);
 #endif
 
 extern int	xactGetCommittedChildren(TransactionId **ptr);
diff --git a/src/include/pgxc/xc_maintenance_mode.h b/src/include/pgxc/xc_maintenance_mode.h
new file mode 100644
index 0000000000..a96148c385
--- /dev/null
+++ b/src/include/pgxc/xc_maintenance_mode.h
@@ -0,0 +1,12 @@
+#ifndef XC_MAINTENANCE_MODE_H
+#define XC_MAINTENANCE_MODE_H
+
+#include <unistd.h>
+#include "c.h"
+#include "postgres.h"
+#include "utils/guc.h"
+
+extern bool xc_maintenance_mode;
+extern GucContext	currentGucContext;
+
+#endif /* XC_MAINTENANCE_MODE_H */
diff --git a/src/include/utils/guc_tables.h b/src/include/utils/guc_tables.h
index 645599b2ab..82fa92c5fd 100644
--- a/src/include/utils/guc_tables.h
+++ b/src/include/utils/guc_tables.h
@@ -93,10 +93,15 @@ enum config_group
 	ERROR_HANDLING_OPTIONS,
 	PRESET_OPTIONS,
 	CUSTOM_OPTIONS,
+#ifdef PGXC
 	DEVELOPER_OPTIONS,
 	DATA_NODES,
 	GTM,
-	COORDINATORS
+	COORDINATORS,
+	XC_HOUSEKEEPING_OPTIONS
+#else
+	DEVELOPER_OPTIONS
+#endif
 };
 
 /*