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The branch, pgxc-barrier has been created
        at  df86ba5f78e6f0a350a229ef565536ca4b5826f8 (commit)

- Log -----------------------------------------------------------------
commit df86ba5f78e6f0a350a229ef565536ca4b5826f8
Author: Pavan Deolasee <pav...@gm...>
Date:   Tue Mar 8 16:45:12 2011 +0530

    First cut implementation of BARRIER for PITR and global consistent recovery

diff --git a/src/backend/access/transam/rmgr.c b/src/backend/access/transam/rmgr.c
index 0273b0e..70f2e42 100644
--- a/src/backend/access/transam/rmgr.c
+++ b/src/backend/access/transam/rmgr.c
@@ -20,9 +20,11 @@
 #include "commands/dbcommands.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#ifdef PGXC
+#include "pgxc/barrier.h"
+#endif
 #include "storage/freespace.h"
 
-
 const RmgrData RmgrTable[RM_MAX_ID + 1] = {
 	{"XLOG", xlog_redo, xlog_desc, NULL, NULL, NULL},
 	{"Transaction", xact_redo, xact_desc, NULL, NULL, NULL},
@@ -40,4 +42,8 @@ const RmgrData RmgrTable[RM_MAX_ID + 1] = {
 	{"Gin", gin_redo, gin_desc, gin_xlog_startup, gin_xlog_cleanup, gin_safe_restartpoint},
 	{"Gist", gist_redo, gist_desc, gist_xlog_startup, gist_xlog_cleanup, gist_safe_restartpoint},
 	{"Sequence", seq_redo, seq_desc, NULL, NULL, NULL}
+#ifdef PGXC	
+	,
+	{"Barrier", barrier_redo, barrier_desc, NULL, NULL, NULL}
+#endif
 };
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 8ff88dd..1f3b218 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -38,6 +38,7 @@
 #include "funcapi.h"
 #include "libpq/pqsignal.h"
 #include "miscadmin.h"
+#include "pgxc/barrier.h"
 #include "pgstat.h"
 #include "postmaster/bgwriter.h"
 #include "storage/bufmgr.h"
@@ -166,6 +167,7 @@ static bool recoveryTargetInclusive = true;
 static TransactionId recoveryTargetXid;
 static TimestampTz recoveryTargetTime;
 static TimestampTz recoveryLastXTime = 0;
+static char *recoveryTargetBarrierId;
 
 /* if recoveryStopsHere returns true, it saves actual stop xid/time here */
 static TransactionId recoveryStopXid;
@@ -4927,6 +4929,13 @@ readRecoveryCommandFile(void)
 			ereport(LOG,
 					(errmsg("recovery_target_inclusive = %s", tok2)));
 		}
+#ifdef PGXC
+		else if (strcmp(tok1, "recovery_barrier_id") == 0)
+		{
+			recoveryTarget = true;
+			recoveryTargetBarrierId = pstrdup(tok2);
+		}
+#endif
 		else
 			ereport(FATAL,
 					(errmsg("unrecognized recovery parameter \"%s\"",
@@ -5109,11 +5118,20 @@ static bool
 recoveryStopsHere(XLogRecord *record, bool *includeThis)
 {
 	bool		stopsHere;
+#ifdef PGXC
+	bool		stopsAtThisBarrier;
+	char		*recordBarrierId;
+#endif
 	uint8		record_info;
 	TimestampTz recordXtime;
 
+#ifdef PGXC
+	/* We only consider stoppping at COMMIT, ABORT or BARRIER records */
+	if ((record->xl_rmid != RM_XACT_ID) && (record->xl_rmid != RM_BARRIER_ID))
+#else
 	/* We only consider stopping at COMMIT or ABORT records */
 	if (record->xl_rmid != RM_XACT_ID)
+#endif
 		return false;
 	record_info = record->xl_info & ~XLR_INFO_MASK;
 	if (record_info == XLOG_XACT_COMMIT)
@@ -5130,6 +5148,12 @@ recoveryStopsHere(XLogRecord *record, bool *includeThis)
 		recordXactAbortData = (xl_xact_abort *) XLogRecGetData(record);
 		recordXtime = recordXactAbortData->xact_time;
 	}
+#ifdef PGXC
+	else if (record_info == XLOG_BARRIER_CREATE)
+	{
+		recordBarrierId = (char *) XLogRecGetData(record);
+	}
+#endif	
 	else
 		return false;
 
@@ -5155,6 +5179,13 @@ recoveryStopsHere(XLogRecord *record, bool *includeThis)
 		if (stopsHere)
 			*includeThis = recoveryTargetInclusive;
 	}
+#ifdef PGXC
+	else if (recoveryTargetBarrierId)
+	{
+		if (strcmp(recoveryTargetBarrierId, recordBarrierId) == 0)
+			stopsAtThisBarrier = true;
+	}
+#endif
 	else
 	{
 		/*
@@ -5206,6 +5237,17 @@ recoveryStopsHere(XLogRecord *record, bool *includeThis)
 		if (recoveryStopAfter)
 			recoveryLastXTime = recordXtime;
 	}
+#ifdef PGXC
+	else if (stopsAtThisBarrier)
+	{
+		recoveryStopTime = recordXtime;
+		ereport(LOG,
+				(errmsg("recovery stopping at barrier %s, time %s",
+						recoveryTargetBarrierId,
+						timestamptz_to_str(recoveryStopTime))));
+		return true;
+	}
+#endif
 	else
 		recoveryLastXTime = recordXtime;
 
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 13e47e9..d980e5f 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -3592,6 +3592,18 @@ _copyValue(Value *from)
 	return newnode;
 }
 
+#ifdef PGXC
+static BarrierStmt *
+_copyBarrierStmt(BarrierStmt *from)
+{
+	BarrierStmt *newnode = makeNode(BarrierStmt);
+
+	COPY_STRING_FIELD(id);
+
+	return newnode;
+}
+#endif
+
 /*
  * copyObject
  *
@@ -4152,6 +4164,11 @@ copyObject(void *from)
 		case T_CheckPointStmt:
 			retval = (void *) makeNode(CheckPointStmt);
 			break;
+#ifdef PGXC
+		case T_BarrierStmt:
+			retval = _copyBarrierStmt(from);
+			break;
+#endif
 		case T_CreateSchemaStmt:
 			retval = _copyCreateSchemaStmt(from);
 			break;
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index 32ac010..fbe5074 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -2306,6 +2306,16 @@ _equalValue(Value *a, Value *b)
 	return true;
 }
 
+#ifdef PGXC
+
+static bool
+_equalBarrierStmt(BarrierStmt *a, BarrierStmt *b)
+{
+	COMPARE_STRING_FIELD(id);
+	return true;
+}
+#endif
+
 /*
  * equal
  *	  returns whether two nodes are equal
@@ -2744,6 +2754,11 @@ equal(void *a, void *b)
 		case T_CheckPointStmt:
 			retval = true;
 			break;
+#ifdef PGXC
+		case T_BarrierStmt:
+			retval = _equalBarrierStmt(a, b);
+			break;
+#endif
 		case T_CreateSchemaStmt:
 			retval = _equalCreateSchemaStmt(a, b);
 			break;
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index e1266ed..6df0582 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -215,6 +215,7 @@ static TypeName *TableFuncTypeName(List *columns);
 		DeallocateStmt PrepareStmt ExecuteStmt
 		DropOwnedStmt ReassignOwnedStmt
 		AlterTSConfigurationStmt AlterTSDictionaryStmt
+		BarrierStmt
 
 %type <node>	select_no_parens select_with_parens select_clause
 				simple_select values_clause
@@ -424,6 +425,7 @@ static TypeName *TableFuncTypeName(List *columns);
 %type <str>		opt_existing_window_name
 %type <ival>	opt_frame_clause frame_extent frame_bound
 /* PGXC_BEGIN */
+%type <str>		opt_barrier_id
 %type <distby>	OptDistributeBy
 /* PGXC_END */
 
@@ -436,12 +438,12 @@ static TypeName *TableFuncTypeName(List *columns);
  */
 
 /* ordinary key words in alphabetical order */
-/* PGXC - added REPLICATION, DISTRIBUTE, MODULO and HASH */
+/* PGXC - added REPLICATION, DISTRIBUTE, MODULO, BARRIER and HASH */
 %token <keyword> ABORT_P ABSOLUTE_P ACCESS ACTION ADD_P ADMIN AFTER
 	AGGREGATE ALL ALSO ALTER ALWAYS ANALYSE ANALYZE AND ANY ARRAY AS ASC
 	ASSERTION ASSIGNMENT ASYMMETRIC AT AUTHORIZATION
 
-	BACKWARD BEFORE BEGIN_P BETWEEN BIGINT BINARY BIT
+	BACKWARD BARRIER BEFORE BEGIN_P BETWEEN BIGINT BINARY BIT
 	BOOLEAN_P BOTH BY
 
 	CACHE CALLED CASCADE CASCADED CASE CAST CATALOG_P CHAIN CHAR_P
@@ -636,6 +638,7 @@ stmt :
 			| AlterUserSetStmt
 			| AlterUserStmt
 			| AnalyzeStmt
+			| BarrierStmt
 			| CheckPointStmt
 			| CleanConnStmt
 			| ClosePortalStmt
@@ -6506,6 +6509,28 @@ opt_name_list:
 		;
 
 
+/* PGXC_BEGIN */
+BarrierStmt: CREATE BARRIER opt_barrier_id
+				{
+					BarrierStmt *n = makeNode(BarrierStmt);
+					n->id = $3;
+					$$ = (Node *)n;
+				}
+			;
+
+opt_barrier_id:
+				Sconst
+				{
+					$$ = pstrdup($1);
+				}
+			| /* EMPTY */
+				{
+					$$ = NULL;
+				}
+			;
+
+/* PGXC_END */
+
 /*****************************************************************************
  *
  *		QUERY:
@@ -10289,7 +10314,7 @@ ColLabel:	IDENT									{ $$ = $1; }
 
 /* "Unreserved" keywords --- available for use as any kind of name.
  */
-/* PGXC - added DISTRIBUTE, HASH, REPLICATION, MODULO */
+/* PGXC - added DISTRIBUTE, HASH, REPLICATION, MODULO, BARRIER */
 unreserved_keyword:
 			  ABORT_P
 			| ABSOLUTE_P
@@ -10306,6 +10331,9 @@ unreserved_keyword:
 			| ASSIGNMENT
 			| AT
 			| BACKWARD
+/* PGXC_BEGIN */
+			| BARRIER
+/* PGXC_END */
 			| BEFORE
 			| BEGIN_P
 			| BY
diff --git a/src/backend/pgxc/Makefile b/src/backend/pgxc/Makefile
index eecac20..ad6bb64 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
+SUBDIRS	    = locator plan pool barrier
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/pgxc/barrier/Makefile b/src/backend/pgxc/barrier/Makefile
new file mode 100644
index 0000000..d80bbec
--- /dev/null
+++ b/src/backend/pgxc/barrier/Makefile
@@ -0,0 +1,19 @@
+#-------------------------------------------------------------------------
+#
+# Makefile--
+#    Makefile for pool
+#
+#  Portions Copyright (c) 2010-2011 Nippon Telegraph and Telephone Corporation
+#
+# IDENTIFICATION
+#    $PostgreSQL$
+#
+#-------------------------------------------------------------------------
+
+subdir = src/backend/pgxc/barrier
+top_builddir = ../../../..
+include $(top_builddir)/src/Makefile.global
+
+OBJS = barrier.o
+
+include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/pgxc/barrier/barrier.c b/src/backend/pgxc/barrier/barrier.c
new file mode 100644
index 0000000..3e1d7cc
--- /dev/null
+++ b/src/backend/pgxc/barrier/barrier.c
@@ -0,0 +1,493 @@
+/*-------------------------------------------------------------------------
+ *
+ * barrier.c
+ *
+ *	  Barrier handling for PITR
+ *
+ *
+ * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
+ * Portions Copyright (c) 2010-2011 Nippon Telegraph and Telephone Corporation
+ *
+ * IDENTIFICATION
+ *	  $$
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+#include "libpq/libpq.h"
+#include "libpq/pqformat.h"
+#include "pgxc/barrier.h"
+#include "pgxc/execRemote.h"
+#include "pgxc/locator.h"
+#include "pgxc/pgxc.h"
+#include "pgxc/pgxcnode.h"
+#include "storage/lwlock.h"
+#include "tcop/dest.h"
+
+static const char *generate_barrier_id(const char *id);
+static PGXCNodeAllHandles *PrepareBarrier(const char *id);
+static void ExecuteBarrier(const char *id);
+static void EndBarrier(PGXCNodeAllHandles *handles, const char *id);
+
+extern void ProcessCreateBarrierPrepare(const char *id);
+extern void ProcessCreateBarrierEnd(const char *id);
+extern void ProcessCreateBarrierExecute(const char *id);
+
+/*
+ * Prepare ourselves for an incoming BARRIER. We must disable all new 2PC
+ * commits and let the ongoing commits to finish. We then remember the
+ * barrier id (so that it can be matched with the final END message) and
+ * tell the driving coordinator to proceed with the next step.
+ *
+ * A simple way to implement this is to grab a lock in an exclusive mode
+ * while all other backend starting a 2PC will grab the lock in shared
+ * mode. So as long as we hold the exclusive lock, no other backend start a
+ * new 2PC and there can not be any 2PC in-progress. This technique would
+ * rely on assumption that an exclsuive lock requester is not starved by
+ * share lock requesters.
+ *
+ * Note: To ensure that the 2PC are not blocked for a long time, we should
+ * set a timeout. The lock should be release after the timeout and the
+ * barrier should be canceled.
+ */
+void
+ProcessCreateBarrierPrepare(const char *id)
+{
+	StringInfoData buf;
+
+	if (!IS_PGXC_COORDINATOR || !IsConnFromCoord())
+		ereport(ERROR,
+				(errcode(ERRCODE_INTERNAL_ERROR),
+				 errmsg("The CREATE BARRIER PREPARE message is expected to "
+						"arrive at a coordinator from another coordinator")));
+
+	LWLockAcquire(BarrierLock, LW_EXCLUSIVE);
+
+	pq_beginmessage(&buf, 'b');
+	pq_sendstring(&buf, id);
+	pq_endmessage(&buf);
+	pq_flush();
+
+	/*
+	 * TODO Start a timer to terminate the pending barrier after a specified
+	 * timeout
+	 */
+}
+
+/*
+ * Mark the completetion of an on-going barrier. We must have remembered the
+ * barrier ID when we received the CREATE BARRIER PREPARE command
+ */
+void
+ProcessCreateBarrierEnd(const char *id)
+{
+	StringInfoData buf;
+
+	if (!IS_PGXC_COORDINATOR || !IsConnFromCoord())
+		ereport(ERROR,
+				(errcode(ERRCODE_INTERNAL_ERROR),
+				 errmsg("The CREATE BARRIER END message is expected to "
+						"arrive at a coordinator from another coordinator")));
+
+	LWLockRelease(BarrierLock);
+
+	pq_beginmessage(&buf, 'b');
+	pq_sendstring(&buf, id);
+	pq_endmessage(&buf);
+	pq_flush();
+
+	/*
+	 * TODO Stop the timer
+	 */
+}
+
+/*
+ * Execute the CREATE BARRIER comamnd. Write a BARRIER WAL record and flush the
+ * WAL buffers to disk before returning to the caller. Writing the WAL record
+ * does not guarantee successful completion of the barrier command.
+ */
+void
+ProcessCreateBarrierExecute(const char *id)
+{
+	StringInfoData buf;
+
+	if (!IsConnFromCoord())
+		ereport(ERROR,
+				(errcode(ERRCODE_INTERNAL_ERROR),
+				 errmsg("The CREATE BARRIER EXECUTE message is expected to "
+						"arrive from a coordinator")));
+	{
+		XLogRecData rdata[1];
+		XLogRecPtr recptr;
+
+		rdata[0].data = (char *) id;
+		rdata[0].len = strlen(id) + 1;
+		rdata[0].buffer = InvalidBuffer;
+		rdata[0].next = NULL;
+
+		recptr = XLogInsert(RM_BARRIER_ID, XLOG_BARRIER_CREATE, rdata);
+		XLogFlush(recptr);
+	}
+
+	pq_beginmessage(&buf, 'b');
+	pq_sendstring(&buf, id);
+	pq_endmessage(&buf);
+	pq_flush();
+}
+
+static const char *
+generate_barrier_id(const char *id)
+{
+	/*
+	 * TODO If the caller can passeed a NULL value, generate an id which is
+	 * guaranteed to be unique across the cluster. We can use a combination of
+	 * the coordinator node id and a timestamp. This may not be complete if we
+	 * support changing coordinator ids without initdb or the system clocks are
+	 * modified.
+	 *
+	 * Another option would be to let the GTM issue globally unique barrier
+	 * IDs. For the time being, we leave it to the user to come up with an
+	 * unique identifier
+	 */
+	return id ? id : pstrdup("dummy_barrier_id");
+}
+
+static PGXCNodeAllHandles *
+SendBarrierPrepareRequest(List *coords, const char *id)
+{
+	PGXCNodeAllHandles *coord_handles;
+	int conn;
+	int msglen;
+	int barrier_idlen;
+
+	coord_handles = get_handles(NIL, coords, true);	
+
+	for (conn = 0; conn < coord_handles->co_conn_count; conn++)
+	{
+		PGXCNodeHandle *handle = coord_handles->coord_handles[conn];
+
+		/* Invalid connection state, return error */
+		if (handle->state != DN_CONNECTION_STATE_IDLE)
+			ereport(ERROR,
+					(errcode(ERRCODE_INTERNAL_ERROR),
+					 errmsg("Failed to send CREATE BARRIER PREPARE request "
+						 	"to the node")));
+
+		barrier_idlen = strlen(id) + 1;
+
+		msglen = 4; /* for the length itself */
+		msglen += barrier_idlen;
+		msglen += 1; /* for barrier command itself */
+
+		/* msgType + msgLen */
+		if (ensure_out_buffer_capacity(handle->outEnd + 1 + msglen, handle) != 0)
+		{
+			ereport(ERROR,
+					(errcode(ERRCODE_INTERNAL_ERROR),
+					 errmsg("Out of memory")));
+		}
+
+		handle->outBuffer[handle->outEnd++] = 'b';
+		msglen = htonl(msglen);
+		memcpy(handle->outBuffer + handle->outEnd, &msglen, 4);
+		handle->outEnd += 4;
+
+		handle->outBuffer[handle->outEnd++] = CREATE_BARRIER_PREPARE;
+
+		memcpy(handle->outBuffer + handle->outEnd, id, barrier_idlen);
+		handle->outEnd += barrier_idlen;
+
+		handle->state = DN_CONNECTION_STATE_QUERY;
+
+		pgxc_node_flush(handle);
+
+		/* FIXME Use the right context */
+		handle->barrier_id = strdup(id);
+	}
+
+	return coord_handles;
+}
+
+static void
+CheckBarrierCommandStatus(PGXCNodeAllHandles *conn_handles, const char *id,
+						  const char *command)
+{
+	int conn;
+	int count = conn_handles->co_conn_count + conn_handles->dn_conn_count;
+
+	elog(DEBUG2, "Check CREATE BARRIER <%s> %s command status", id, command);
+
+	for (conn = 0; conn < count; conn++)
+	{
+		PGXCNodeHandle *handle;
+	   
+		if (conn < conn_handles->co_conn_count)
+			handle = conn_handles->coord_handles[conn];
+		else
+			handle = conn_handles->datanode_handles[conn - conn_handles->co_conn_count];
+
+		if (pgxc_node_receive(1, &handle, NULL))
+			ereport(ERROR,
+					(errcode(ERRCODE_INTERNAL_ERROR),
+					 errmsg("Failed to receive response from the remote side")));
+
+		if (handle_response(handle, NULL) != RESPONSE_BARRIER_OK)
+			ereport(ERROR,
+					(errcode(ERRCODE_INTERNAL_ERROR),
+					 errmsg("CREATE BARRIER PREPARE command failed "
+						 	"with error %s", handle->error)));
+	}
+
+	elog(DEBUG2, "Successfully completed CREATE BARRIER <%s> %s command on "
+				 "all nodes", id, command);
+}
+
+static void
+SendBarrierEndRequest(PGXCNodeAllHandles *coord_handles, const char *id)
+{
+	int conn;
+	int msglen;
+	int barrier_idlen;
+
+	elog(DEBUG2, "Sending CREATE BARRIER <%s> END command to all coordinators", id);
+
+	for (conn = 0; conn < coord_handles->co_conn_count; conn++)
+	{
+		PGXCNodeHandle *handle = coord_handles->coord_handles[conn];
+
+		/* Invalid connection state, return error */
+		if (handle->state != DN_CONNECTION_STATE_IDLE)
+			ereport(ERROR,
+					(errcode(ERRCODE_INTERNAL_ERROR),
+					 errmsg("Failed to send CREATE BARRIER PREPARE request "
+						 	"to the node")));
+
+		barrier_idlen = strlen(id) + 1;
+
+		msglen = 4; /* for the length itself */
+		msglen += barrier_idlen;
+		msglen += 1; /* for barrier command itself */
+
+		/* msgType + msgLen */
+		if (ensure_out_buffer_capacity(handle->outEnd + 1 + msglen, handle) != 0)
+		{
+			ereport(ERROR,
+					(errcode(ERRCODE_INTERNAL_ERROR),
+					 errmsg("Out of memory")));
+		}
+
+		handle->outBuffer[handle->outEnd++] = 'b';
+		msglen = htonl(msglen);
+		memcpy(handle->outBuffer + handle->outEnd, &msglen, 4);
+		handle->outEnd += 4;
+
+		handle->outBuffer[handle->outEnd++] = CREATE_BARRIER_END;
+
+		memcpy(handle->outBuffer + handle->outEnd, id, barrier_idlen);
+		handle->outEnd += barrier_idlen;
+
+		handle->state = DN_CONNECTION_STATE_QUERY;
+		pgxc_node_flush(handle);
+
+		/* FIXME Use the right context */
+		handle->barrier_id = strdup(id);
+	}
+
+}
+
+/*
+ * Prepare all coordinators for barrier. During this step all the coordinators
+ * are informed to suspend any new 2PC transactions. The coordinators should
+ * disable new 2PC transactions and then wait for the existing transactions to
+ * complete. Once all "in-flight" 2PC transactions are over, the coordinators
+ * respond back.
+ *
+ * That completes the first step in barrier generation
+ *
+ * Any errors will be reported via ereport.
+ */ 
+static PGXCNodeAllHandles *
+PrepareBarrier(const char *id)
+{
+	PGXCNodeAllHandles *coord_handles;
+
+	elog(DEBUG2, "Preparing coordinators for BARRIER");
+
+	/*
+	 * Send a CREATE BARRIER PREPARE message to all the coordinators. We should
+	 * send an asynchronous request so that we can disable local commits and
+	 * then wait for the remote coordinators to finish the work
+	 */
+	coord_handles = SendBarrierPrepareRequest(GetAllCoordNodes(), id);
+
+	/*
+	 * Disable local commits
+	 */
+	LWLockAcquire(BarrierLock, LW_EXCLUSIVE);
+
+	elog(DEBUG2, "Disabled 2PC commits origniating at the diriving coordinator");
+
+	/*
+	 * TODO Start a timer to cancel the barrier request in case of a timeout
+	 */
+
+	/*
+	 * Local in-flight commits are now over. Check status of the remote
+	 * coordinators
+	 */
+	CheckBarrierCommandStatus(coord_handles, id, "PREPARE");
+
+	return coord_handles;
+}
+
+/*
+ * Execute the barrier command on all the components, including data nodes and
+ * coordinators. 
+ */
+static void
+ExecuteBarrier(const char *id)
+{
+	List *barrierDataNodeList = GetAllDataNodes();
+	List *barrierCoordList = GetAllCoordNodes();
+	PGXCNodeAllHandles *conn_handles;
+	int conn;
+	int msglen;
+	int barrier_idlen;
+
+	conn_handles = get_handles(barrierDataNodeList, barrierCoordList, false);
+
+	elog(DEBUG2, "Sending CREATE BARRIER <%s> EXECUTE message to "
+				 "data nodes and coordinator", id);
+	/* 
+	 * Send a CREATE BARRIER request to all the data nodes and the coordinators
+	 */
+	for (conn = 0; conn < conn_handles->co_conn_count + conn_handles->dn_conn_count; conn++)
+	{
+		PGXCNodeHandle *handle;
+	   
+		if (conn < conn_handles->co_conn_count)
+			handle = conn_handles->coord_handles[conn];
+		else
+			handle = conn_handles->datanode_handles[conn - conn_handles->co_conn_count];
+
+		/* Invalid connection state, return error */
+		if (handle->state != DN_CONNECTION_STATE_IDLE)
+			ereport(ERROR,
+					(errcode(ERRCODE_INTERNAL_ERROR),
+					 errmsg("Failed to send CREATE BARRIER PREPARE request "
+						 	"to the node")));
+
+		barrier_idlen = strlen(id) + 1;
+
+		msglen = 4; /* for the length itself */
+		msglen += barrier_idlen;
+		msglen += 1; /* for barrier command itself */
+
+		/* msgType + msgLen */
+		if (ensure_out_buffer_capacity(handle->outEnd + 1 + msglen, handle) != 0)
+		{
+			ereport(ERROR,
+					(errcode(ERRCODE_INTERNAL_ERROR),
+					 errmsg("Out of memory")));
+		}
+
+		handle->outBuffer[handle->outEnd++] = 'b';
+		msglen = htonl(msglen);
+		memcpy(handle->outBuffer + handle->outEnd, &msglen, 4);
+		handle->outEnd += 4;
+
+		handle->outBuffer[handle->outEnd++] = CREATE_BARRIER_EXECUTE;
+
+		memcpy(handle->outBuffer + handle->outEnd, id, barrier_idlen);
+		handle->outEnd += barrier_idlen;
+
+		handle->state = DN_CONNECTION_STATE_QUERY;
+		pgxc_node_flush(handle);
+
+		/* FIXME Use the right context */
+		handle->barrier_id = strdup(id);
+	}
+
+	CheckBarrierCommandStatus(conn_handles, id, "EXECUTE");
+
+	/*
+	 * Also WAL log the BARRIER locally and flush the WAL buffers to disk
+	 */
+}
+
+/*
+ * Resume 2PC commits on the local as well as remote coordinators.
+ */
+static void
+EndBarrier(PGXCNodeAllHandles *prepared_handles, const char *id)
+{
+	/* Resume 2PC locally */
+	LWLockRelease(BarrierLock);
+
+	SendBarrierEndRequest(prepared_handles, id);
+
+	CheckBarrierCommandStatus(prepared_handles, id, "END");
+}
+
+void
+RequestBarrier(const char *id, char *completionTag)
+{
+	PGXCNodeAllHandles *prepared_handles;
+	const char *barrier_id;
+
+	elog(DEBUG2, "CREATE BARRIER request received");
+	/*
+	 * Ensure that we are a coordinator and the request is not from another
+	 * coordinator
+	 */
+	if (!IS_PGXC_COORDINATOR)
+		ereport(ERROR,
+				(errcode(ERRCODE_INTERNAL_ERROR),
+				 errmsg("CREATE BARRIER command must be sent to a coordinator")));
+
+	if (IsConnFromCoord())
+		ereport(ERROR,
+				(errcode(ERRCODE_INTERNAL_ERROR),
+				 errmsg("CREATE BARRIER command is not expected from another coordinator")));
+
+	/*
+	 * Get a barrier id if the user has not supplied it
+	 */
+	barrier_id = generate_barrier_id(id);
+	
+	elog(DEBUG2, "CREATE BARRIER <%s>", barrier_id);
+
+	/*
+	 * Step One. Prepare all coordinators for upcoming barrier request
+	 */
+	prepared_handles = PrepareBarrier(barrier_id);
+
+	/*
+	 * Step two. Issue BARRIER command to all involved components, including
+	 * coordinators and data nodes
+	 */
+	ExecuteBarrier(barrier_id);
+
+	/*
+	 * Step three. Inform coordinators about a successfully completed barrier
+	 */
+	EndBarrier(prepared_handles, barrier_id);
+
+	if (completionTag)
+		snprintf(completionTag, COMPLETION_TAG_BUFSIZE, "BARRIER %s", barrier_id);
+}
+
+void
+barrier_redo(XLogRecPtr lsn, XLogRecord *record)
+{
+	/* Nothing to do */
+	return;
+}
+
+void
+barrier_desc(StringInfo buf, uint8 xl_info, char *rec)
+{
+	Assert(xl_info == XLOG_BARRIER_CREATE);
+	appendStringInfo(buf, "BARRIER %s", rec);
+}
diff --git a/src/backend/pgxc/pool/execRemote.c b/src/backend/pgxc/pool/execRemote.c
index 711cd1f..849f36b 100644
--- a/src/backend/pgxc/pool/execRemote.c
+++ b/src/backend/pgxc/pool/execRemote.c
@@ -1347,6 +1347,7 @@ pgxc_node_receive_responses(const int conn_count, PGXCNodeHandle ** connections,
  * RESPONSE_TUPLEDESC - got tuple description
  * RESPONSE_DATAROW - got data row
  * RESPONSE_COPY - got copy response
+ * RESPONSE_BARRIER_OK - barrier command completed successfully
  */
 int
 handle_response(PGXCNodeHandle * conn, RemoteQueryState *combiner)
@@ -1458,6 +1459,16 @@ handle_response(PGXCNodeHandle * conn, RemoteQueryState *combiner)
 #endif
 				return result;
 			}
+
+#ifdef PGXC
+			case 'b':
+				{
+					Assert((strncmp(msg, conn->barrier_id, msg_len) == 0));
+					conn->state = DN_CONNECTION_STATE_IDLE;
+					return RESPONSE_BARRIER_OK;
+				}
+#endif
+
 			case 'I':			/* EmptyQuery */
 			default:
 				/* sync lost? */
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 9615b52..b06b7bf 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -78,6 +78,7 @@
 #include "access/gtm.h"
 /* PGXC_COORD */
 #include "pgxc/execRemote.h"
+#include "pgxc/barrier.h"
 #include "pgxc/planner.h"
 #include "pgxc/pgxcnode.h"
 #include "commands/copy.h"
@@ -430,6 +431,7 @@ SocketBackend(StringInfo inBuf)
 		case 'g':				/* GXID */
 		case 's':				/* Snapshot */
 		case 't':				/* Timestamp */
+		case 'b':				/* Barrier */
 			break;
 #endif
 
@@ -4031,6 +4033,37 @@ PostgresMain(int argc, char *argv[], const char *username)
 				 */
 				SetCurrentGTMDeltaTimestamp(timestamp);
 				break;
+
+			case 'b':			/* barrier */
+				{
+					int command;
+					char *id;
+
+					command = pq_getmsgbyte(&input_message);
+					id = pq_getmsgstring(&input_message);
+					pq_getmsgend(&input_message);
+
+					switch (command)
+					{
+						case CREATE_BARRIER_PREPARE:
+							ProcessCreateBarrierPrepare(id);
+							break;
+
+						case CREATE_BARRIER_END:
+							ProcessCreateBarrierEnd(id);
+							break;
+
+						case CREATE_BARRIER_EXECUTE:
+							ProcessCreateBarrierExecute(id);
+							break;
+
+						default:
+							ereport(ERROR,
+									(errcode(ERRCODE_INTERNAL_ERROR),
+									 errmsg("Invalid command received")));
+					}
+				}
+				break;
 #endif /* PGXC */
 
 			default:
diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
index 065d880..bd13ce3 100644
--- a/src/backend/tcop/utility.c
+++ b/src/backend/tcop/utility.c
@@ -58,6 +58,7 @@
 #include "utils/syscache.h"
 
 #ifdef PGXC
+#include "pgxc/barrier.h"
 #include "pgxc/locator.h"
 #include "pgxc/pgxc.h"
 #include "pgxc/planner.h"
@@ -1347,6 +1348,12 @@ ProcessUtility(Node *parsetree,
 #endif
 			break;
 
+#ifdef PGXC
+		case T_BarrierStmt:
+			RequestBarrier(((BarrierStmt *) parsetree)->id, completionTag);
+			break;
+#endif
+
 		case T_ReindexStmt:
 			{
 				ReindexStmt *stmt = (ReindexStmt *) parsetree;
@@ -2320,6 +2327,12 @@ CreateCommandTag(Node *parsetree)
 			tag = "CHECKPOINT";
 			break;
 
+#ifdef PGXC
+		case T_BarrierStmt:
+			tag = "BARRIER";
+			break;
+#endif
+
 		case T_ReindexStmt:
 			tag = "REINDEX";
 			break;
diff --git a/src/include/access/rmgr.h b/src/include/access/rmgr.h
index 5702f5f..a46e7fe 100644
--- a/src/include/access/rmgr.h
+++ b/src/include/access/rmgr.h
@@ -30,6 +30,11 @@ typedef uint8 RmgrId;
 #define RM_GIN_ID				13
 #define RM_GIST_ID				14
 #define RM_SEQ_ID				15
+#ifdef PGXC
+#define RM_BARRIER_ID			16
+#define RM_MAX_ID				RM_BARRIER_ID
+#else
 #define RM_MAX_ID				RM_SEQ_ID
+#endif
 
 #endif   /* RMGR_H */
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index 6776c25..e4ff851 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -319,6 +319,9 @@ typedef enum NodeTag
 	T_ConstraintsSetStmt,
 	T_ReindexStmt,
 	T_CheckPointStmt,
+#ifdef PGXC
+	T_BarrierStmt,
+#endif
 	T_CreateSchemaStmt,
 	T_AlterDatabaseStmt,
 	T_AlterDatabaseSetStmt,
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 951484c..7398649 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -2201,6 +2201,19 @@ typedef struct VacuumStmt
 	List	   *va_cols;		/* list of column names, or NIL for all */
 } VacuumStmt;
 
+#ifdef PGXC
+/*
+ * ----------------------
+ *      Barrier Statement
+ */
+typedef struct BarrierStmt
+{
+	NodeTag		type;
+	const char	*id;			/* User supplied barrier id, if any */
+} BarrierStmt;
+
+#endif
+
 /* ----------------------
  *		Explain Statement
  * ----------------------
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
index 2c84923..6993eee 100644
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -52,6 +52,9 @@ PG_KEYWORD("asymmetric", ASYMMETRIC, RESERVED_KEYWORD)
 PG_KEYWORD("at", AT, UNRESERVED_KEYWORD)
 PG_KEYWORD("authorization", AUTHORIZATION, TYPE_FUNC_NAME_KEYWORD)
 PG_KEYWORD("backward", BACKWARD, UNRESERVED_KEYWORD)
+#ifdef PGXC
+PG_KEYWORD("barrier", BARRIER, UNRESERVED_KEYWORD)
+#endif
 PG_KEYWORD("before", BEFORE, UNRESERVED_KEYWORD)
 PG_KEYWORD("begin", BEGIN_P, UNRESERVED_KEYWORD)
 PG_KEYWORD("between", BETWEEN, TYPE_FUNC_NAME_KEYWORD)
diff --git a/src/include/pgxc/barrier.h b/src/include/pgxc/barrier.h
new file mode 100644
index 0000000..37b5067
--- /dev/null
+++ b/src/include/pgxc/barrier.h
@@ -0,0 +1,40 @@
+/*-------------------------------------------------------------------------
+ *
+ * barrier.h
+ *
+ *	  Definitions for the PITR barrier handling
+ *
+ *
+ * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
+ * Portions Copyright (c) 2010-2011 Nippon Telegraph and Telephone Corporation
+ *
+ * IDENTIFICATION
+ *	  $$
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef BARRIER_H
+#define BARRIER_H
+
+#include "access/xlog.h"
+#include "access/xlogdefs.h"
+
+#define CREATE_BARRIER_PREPARE	'P'
+#define CREATE_BARRIER_EXECUTE	'X'
+#define CREATE_BARRIER_END		'E'
+
+#define CREATE_BARRIER_PREPARE_DONE	'p'
+#define CREATE_BARRIER_EXECUTE_DONE	'x'
+
+typedef struct xl_barrier
+{
+	char	barrier_id[1];	/* variable length data follows */
+} xl_barrier;
+
+#define XLOG_BARRIER_CREATE	0x00
+
+extern void RequestBarrier(const char *id, char *completionTag);
+extern void barrier_redo(XLogRecPtr lsn, XLogRecord *record);
+extern void barrier_desc(StringInfo buf, uint8 xl_info, char *rec);
+#endif
diff --git a/src/include/pgxc/execRemote.h b/src/include/pgxc/execRemote.h
index 23ea4a8..e9f000f 100644
--- a/src/include/pgxc/execRemote.h
+++ b/src/include/pgxc/execRemote.h
@@ -36,6 +36,7 @@
 #define RESPONSE_TUPDESC 2
 #define RESPONSE_DATAROW 3
 #define RESPONSE_COPY 4
+#define RESPONSE_BARRIER_OK 5
 
 typedef enum
 {
diff --git a/src/include/pgxc/pgxcnode.h b/src/include/pgxc/pgxcnode.h
index f8ac7c6..38fe895 100644
--- a/src/include/pgxc/pgxcnode.h
+++ b/src/include/pgxc/pgxcnode.h
@@ -66,6 +66,7 @@ struct pgxc_node_handle
 #ifdef DN_CONNECTION_DEBUG
 	bool		have_row_desc;
 #endif
+	char	   *barrier_id;
 	char	   *error;
 	/* Output buffer */
 	char	   *outBuffer;
diff --git a/src/include/storage/lwlock.h b/src/include/storage/lwlock.h
index 0548159..398ebd9 100644
--- a/src/include/storage/lwlock.h
+++ b/src/include/storage/lwlock.h
@@ -69,6 +69,7 @@ typedef enum LWLockId
 	SyncScanLock,
 #ifdef PGXC
 	AnalyzeProcArrayLock,
+	BarrierLock,
 #endif
 	/* Individual lock IDs end here */
 	FirstBufMappingLock,

-----------------------------------------------------------------------


hooks/post-receive
-- 
Postgres-XC