diff --git a/Makefile b/Makefile
index 10841d743..43ca841c4 100644
--- a/Makefile
+++ b/Makefile
@@ -13,14 +13,14 @@ include Makefile.global
 all: extension
 
 # build extension
-extension:
+extension: $(citus_abs_srcdir)/src/include/citus_version.h
 	$(MAKE) -C src/backend/distributed/ all
 install-extension: extension
 	$(MAKE) -C src/backend/distributed/ install
 install-headers: extension
 	$(MKDIR_P) '$(DESTDIR)$(includedir_server)/distributed/'
 # generated headers are located in the build directory
-	$(INSTALL_DATA) src/include/citus_config.h '$(DESTDIR)$(includedir_server)/'
+	$(INSTALL_DATA) $(citus_abs_srcdir)/src/include/citus_version.h '$(DESTDIR)$(includedir_server)/'
 # the rest in the source tree
 	$(INSTALL_DATA) $(citus_abs_srcdir)/src/include/distributed/*.h '$(DESTDIR)$(includedir_server)/distributed/'
 clean-extension:
diff --git a/Makefile.global.in b/Makefile.global.in
index 7cdbcd5d9..57678e137 100644
--- a/Makefile.global.in
+++ b/Makefile.global.in
@@ -44,8 +44,8 @@ $(citus_top_builddir)/Makefile.global: $(citus_abs_top_srcdir)/configure $(citus
 
 # Ensure configuration is generated by the most recent configure,
 # useful for longer existing build directories.
-$(citus_top_builddir)/config.status: $(citus_abs_top_srcdir)/configure
-	cd @abs_top_builddir@ && ./config.status --recheck
+$(citus_top_builddir)/config.status: $(citus_abs_top_srcdir)/configure $(citus_abs_top_srcdir)/src/backend/distributed/citus.control
+	cd @abs_top_builddir@ && ./config.status --recheck && ./config.status
 
 # Regenerate configure if configure.in changed
 $(citus_abs_top_srcdir)/configure: $(citus_abs_top_srcdir)/configure.in
diff --git a/configure b/configure
index c46b262b8..9cf33a4bd 100755
--- a/configure
+++ b/configure
@@ -1,6 +1,6 @@
 #! /bin/sh
 # Guess values for system-dependent variables and create Makefiles.
-# Generated by GNU Autoconf 2.69 for Citus 5.0.
+# Generated by GNU Autoconf 2.69 for Citus 6.2devel.
 #
 #
 # Copyright (C) 1992-1996, 1998-2012 Free Software Foundation, Inc.
@@ -9,7 +9,7 @@
 # This configure script is free software; the Free Software Foundation
 # gives unlimited permission to copy, distribute and modify it.
 #
-# Copyright (c) 2012-2016, Citus Data, Inc.
+# Copyright (c) 2012-2017, Citus Data, Inc.
 ## -------------------- ##
 ## M4sh Initialization. ##
 ## -------------------- ##
@@ -579,8 +579,8 @@ MAKEFLAGS=
 # Identity of this package.
 PACKAGE_NAME='Citus'
 PACKAGE_TARNAME='citus'
-PACKAGE_VERSION='5.0'
-PACKAGE_STRING='Citus 5.0'
+PACKAGE_VERSION='6.2devel'
+PACKAGE_STRING='Citus 6.2devel'
 PACKAGE_BUGREPORT=''
 PACKAGE_URL=''
 
@@ -600,6 +600,7 @@ vpath_build
 PATH
 PG_CONFIG
 FLEX
+AWK
 SED
 target_alias
 host_alias
@@ -1194,7 +1195,7 @@ if test "$ac_init_help" = "long"; then
   # Omit some internal or obsolete options to make the list less imposing.
   # This message is too long to be a string in the A/UX 3.1 sh.
   cat <<_ACEOF
-\`configure' configures Citus 5.0 to adapt to many kinds of systems.
+\`configure' configures Citus 6.2devel to adapt to many kinds of systems.
 
 Usage: $0 [OPTION]... [VAR=VALUE]...
 
@@ -1255,7 +1256,7 @@ fi
 
 if test -n "$ac_init_help"; then
   case $ac_init_help in
-     short | recursive ) echo "Configuration of Citus 5.0:";;
+     short | recursive ) echo "Configuration of Citus 6.2devel:";;
    esac
   cat <<\_ACEOF
 
@@ -1343,14 +1344,14 @@ fi
 test -n "$ac_init_help" && exit $ac_status
 if $ac_init_version; then
   cat <<\_ACEOF
-Citus configure 5.0
+Citus configure 6.2devel
 generated by GNU Autoconf 2.69
 
 Copyright (C) 2012 Free Software Foundation, Inc.
 This configure script is free software; the Free Software Foundation
 gives unlimited permission to copy, distribute and modify it.
 
-Copyright (c) 2012-2016, Citus Data, Inc.
+Copyright (c) 2012-2017, Citus Data, Inc.
 _ACEOF
   exit
 fi
@@ -1400,7 +1401,7 @@ cat >config.log <<_ACEOF
 This file contains any messages produced by compilers while
 running configure, to aid debugging if configure makes a mistake.
 
-It was created by Citus $as_me 5.0, which was
+It was created by Citus $as_me 6.2devel, which was
 generated by GNU Autoconf 2.69.  Invocation command line was
 
   $ $0 $@
@@ -1750,6 +1751,7 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
 
+# we'll need sed and awk for some of the version commands
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for a sed that does not truncate output" >&5
 $as_echo_n "checking for a sed that does not truncate output... " >&6; }
 if ${ac_cv_path_SED+:} false; then :
@@ -1819,6 +1821,82 @@ $as_echo "$ac_cv_path_SED" >&6; }
  SED="$ac_cv_path_SED"
   rm -f conftest.sed
 
+for ac_prog in gawk mawk nawk awk
+do
+  # Extract the first word of "$ac_prog", so it can be a program name with args.
+set dummy $ac_prog; ac_word=$2
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
+$as_echo_n "checking for $ac_word... " >&6; }
+if ${ac_cv_prog_AWK+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  if test -n "$AWK"; then
+  ac_cv_prog_AWK="$AWK" # Let the user override the test.
+else
+as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
+for as_dir in $PATH
+do
+  IFS=$as_save_IFS
+  test -z "$as_dir" && as_dir=.
+    for ac_exec_ext in '' $ac_executable_extensions; do
+  if as_fn_executable_p "$as_dir/$ac_word$ac_exec_ext"; then
+    ac_cv_prog_AWK="$ac_prog"
+    $as_echo "$as_me:${as_lineno-$LINENO}: found $as_dir/$ac_word$ac_exec_ext" >&5
+    break 2
+  fi
+done
+  done
+IFS=$as_save_IFS
+
+fi
+fi
+AWK=$ac_cv_prog_AWK
+if test -n "$AWK"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $AWK" >&5
+$as_echo "$AWK" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+
+  test -n "$AWK" && break
+done
+
+
+# CITUS_VERSION definition
+
+cat >>confdefs.h <<_ACEOF
+#define CITUS_VERSION "$PACKAGE_VERSION"
+_ACEOF
+
+
+# CITUS_MAJORVERSION definition
+CITUS_MAJORVERSION=`expr "$PACKAGE_VERSION" : '\([0-9][0-9]*\.[0-9][0-9]*\)'`
+
+cat >>confdefs.h <<_ACEOF
+#define CITUS_MAJORVERSION "$CITUS_MAJORVERSION"
+_ACEOF
+
+
+# CITUS_VERSION_NUM definition
+# awk -F is a regex on some platforms, and not on others, so make "." a tab
+CITUS_VERSION_NUM="`echo "$PACKAGE_VERSION" | sed 's/[A-Za-z].*$//' |
+tr '.' '	' |
+$AWK '{printf "%d%02d%02d", $1, $2, (NF >= 3) ? $3 : 0}'`"
+
+cat >>confdefs.h <<_ACEOF
+#define CITUS_VERSION_NUM $CITUS_VERSION_NUM
+_ACEOF
+
+
+# CITUS_EXTENSIONVERSION definition
+CITUS_EXTENSIONVERSION="`grep '^default_version' $srcdir/src/backend/distributed/citus.control | cut -d\' -f2`"
+
+cat >>confdefs.h <<_ACEOF
+#define CITUS_EXTENSIONVERSION "$CITUS_EXTENSIONVERSION"
+_ACEOF
+
 
 # Re-check for flex. That allows to compile citus against a postgres
 # which was built without flex available (possible because generated
@@ -2974,7 +3052,7 @@ POSTGRES_BUILDDIR="$POSTGRES_BUILDDIR"
 
 ac_config_files="$ac_config_files Makefile.global"
 
-ac_config_headers="$ac_config_headers src/include/citus_config.h"
+ac_config_headers="$ac_config_headers src/include/citus_config.h src/include/citus_version.h"
 
 
 cat >confcache <<\_ACEOF
@@ -3483,7 +3561,7 @@ cat >>$CONFIG_STATUS <<\_ACEOF || ac_write_fail=1
 # report actual input values of CONFIG_FILES etc. instead of their
 # values after options handling.
 ac_log="
-This file was extended by Citus $as_me 5.0, which was
+This file was extended by Citus $as_me 6.2devel, which was
 generated by GNU Autoconf 2.69.  Invocation command line was
 
   CONFIG_FILES    = $CONFIG_FILES
@@ -3545,7 +3623,7 @@ _ACEOF
 cat >>$CONFIG_STATUS <<_ACEOF || ac_write_fail=1
 ac_cs_config="`$as_echo "$ac_configure_args" | sed 's/^ //; s/[\\""\`\$]/\\\\&/g'`"
 ac_cs_version="\\
-Citus config.status 5.0
+Citus config.status 6.2devel
 configured by $0, generated by GNU Autoconf 2.69,
   with options \\"\$ac_cs_config\\"
 
@@ -3555,6 +3633,7 @@ gives unlimited permission to copy, distribute and modify it."
 
 ac_pwd='$ac_pwd'
 srcdir='$srcdir'
+AWK='$AWK'
 test -n "\$AWK" || AWK=awk
 _ACEOF
 
@@ -3668,6 +3747,7 @@ do
   case $ac_config_target in
     "Makefile.global") CONFIG_FILES="$CONFIG_FILES Makefile.global" ;;
     "src/include/citus_config.h") CONFIG_HEADERS="$CONFIG_HEADERS src/include/citus_config.h" ;;
+    "src/include/citus_version.h") CONFIG_HEADERS="$CONFIG_HEADERS src/include/citus_version.h" ;;
 
   *) as_fn_error $? "invalid argument: \`$ac_config_target'" "$LINENO" 5;;
   esac
diff --git a/configure.in b/configure.in
index 25bcbe666..1bc1a6ee3 100644
--- a/configure.in
+++ b/configure.in
@@ -5,10 +5,30 @@
 # everyone needing autoconf installed, the resulting files are checked
 # into the SCM.
 
-AC_INIT([Citus], [5.0], [], [citus], [])
-AC_COPYRIGHT([Copyright (c) 2012-2016, Citus Data, Inc.])
+AC_INIT([Citus], [6.2devel])
+AC_COPYRIGHT([Copyright (c) 2012-2017, Citus Data, Inc.])
 
+# we'll need sed and awk for some of the version commands
 AC_PROG_SED
+AC_PROG_AWK
+
+# CITUS_VERSION definition
+AC_DEFINE_UNQUOTED(CITUS_VERSION, "$PACKAGE_VERSION", [Citus version as a string])
+
+# CITUS_MAJORVERSION definition
+[CITUS_MAJORVERSION=`expr "$PACKAGE_VERSION" : '\([0-9][0-9]*\.[0-9][0-9]*\)'`]
+AC_DEFINE_UNQUOTED(CITUS_MAJORVERSION, "$CITUS_MAJORVERSION", [Citus major version as a string])
+
+# CITUS_VERSION_NUM definition
+# awk -F is a regex on some platforms, and not on others, so make "." a tab
+[CITUS_VERSION_NUM="`echo "$PACKAGE_VERSION" | sed 's/[A-Za-z].*$//' |
+tr '.' '	' |
+$AWK '{printf "%d%02d%02d", $1, $2, (NF >= 3) ? $3 : 0}'`"]
+AC_DEFINE_UNQUOTED(CITUS_VERSION_NUM, $CITUS_VERSION_NUM, [Citus version as a number])
+
+# CITUS_EXTENSIONVERSION definition
+[CITUS_EXTENSIONVERSION="`grep '^default_version' $srcdir/src/backend/distributed/citus.control | cut -d\' -f2`"]
+AC_DEFINE_UNQUOTED([CITUS_EXTENSIONVERSION], "$CITUS_EXTENSIONVERSION", [Extension version expected by this Citus build])
 
 # Re-check for flex. That allows to compile citus against a postgres
 # which was built without flex available (possible because generated
@@ -122,7 +142,7 @@ AC_SUBST(POSTGRES_SRCDIR, "$POSTGRES_SRCDIR")
 AC_SUBST(POSTGRES_BUILDDIR, "$POSTGRES_BUILDDIR")
 
 AC_CONFIG_FILES([Makefile.global])
-AC_CONFIG_HEADERS([src/include/citus_config.h])
+AC_CONFIG_HEADERS([src/include/citus_config.h] [src/include/citus_version.h])
 AH_TOP([
 /*
  * citus_config.h.in is generated by autoconf/autoheader and
diff --git a/src/backend/distributed/executor/multi_utility.c b/src/backend/distributed/executor/multi_utility.c
index d70fd1930..fad9cad76 100644
--- a/src/backend/distributed/executor/multi_utility.c
+++ b/src/backend/distributed/executor/multi_utility.c
@@ -28,6 +28,7 @@
 #include "catalog/namespace.h"
 #include "catalog/pg_attribute.h"
 #include "catalog/pg_class.h"
+#include "citus_version.h"
 #include "commands/defrem.h"
 #include "commands/tablecmds.h"
 #include "commands/prepare.h"
@@ -82,7 +83,6 @@
 
 bool EnableDDLPropagation = true; /* ddl propagation is enabled */
 
-
 /*
  * This struct defines the state for the callback for drop statements.
  * It is copied as it is from commands/tablecmds.c in Postgres source.
@@ -95,6 +95,10 @@ struct DropRelationCallbackState
 };
 
 
+/* Local functions forward declarations for deciding when to perform processing/checks */
+static bool SkipCitusProcessingForUtility(Node *parsetree);
+static bool IsCitusExtensionStmt(Node *parsetree);
+
 /* Local functions forward declarations for Transmit statement */
 static bool IsTransmitStmt(Node *parsetree);
 static void VerifyTransmitStmt(CopyStmt *copyStatement);
@@ -120,6 +124,7 @@ static char * DeparseVacuumColumnNames(List *columnNameList);
 
 
 /* Local functions forward declarations for unsupported command checks */
+static void ErrorIfUnstableCreateOrAlterExtensionStmt(Node *parsetree);
 static void ErrorIfUnsupportedIndexStmt(IndexStmt *createIndexStatement);
 static void ErrorIfUnsupportedDropIndexStmt(DropStmt *dropIndexStatement);
 static void ErrorIfUnsupportedAlterTableStmt(AlterTableStmt *alterTableStatement);
@@ -130,6 +135,7 @@ static bool OptionsSpecifyOwnedBy(List *optionList, Oid *ownedByTableId);
 static void ErrorIfDistributedRenameStmt(RenameStmt *renameStatement);
 
 /* Local functions forward declarations for helper functions */
+static char * ExtractNewExtensionVersion(Node *parsetree);
 static void CreateLocalTable(RangeVar *relation, char *nodeName, int32 nodePort);
 static bool IsAlterTableRenameStmt(RenameStmt *renameStatement);
 static void ExecuteDistributedDDLJob(DDLJob *ddlJob);
@@ -170,18 +176,20 @@ multi_ProcessUtility(Node *parsetree,
 	Oid savedUserId = InvalidOid;
 	int savedSecurityContext = 0;
 	List *ddlJobs = NIL;
+	bool skipCitusProcessing = SkipCitusProcessingForUtility(parsetree);
 
-	if (IsA(parsetree, TransactionStmt))
+	if (skipCitusProcessing)
 	{
-		/*
-		 * Transaction statements (e.g. ABORT, COMMIT) can be run in aborted
-		 * transactions in which case a lot of checks cannot be done safely in
-		 * that state. Since we never need to intercept transaction statements,
-		 * skip our checks and immediately fall into standard_ProcessUtility.
-		 */
+		bool checkExtensionVersion = IsCitusExtensionStmt(parsetree);
+
 		standard_ProcessUtility(parsetree, queryString, context,
 								params, dest, completionTag);
 
+		if (EnableVersionChecks && checkExtensionVersion)
+		{
+			ErrorIfUnstableCreateOrAlterExtensionStmt(parsetree);
+		}
+
 		return;
 	}
 
@@ -401,6 +409,86 @@ multi_ProcessUtility(Node *parsetree,
 }
 
 
+/*
+ * SkipCitusProcessingForUtility simply returns whether a given utility should
+ * bypass Citus processing and checks and be handled exclusively by standard
+ * PostgreSQL utility processing. At present, CREATE/ALTER/DROP EXTENSION,
+ * ABORT, COMMIT, ROLLBACK, and SET (GUC) statements are exempt from Citus.
+ */
+static bool
+SkipCitusProcessingForUtility(Node *parsetree)
+{
+	switch (parsetree->type)
+	{
+		/*
+		 * In the CitusHasBeenLoaded check, we compare versions of loaded code,
+		 * the installed extension, and available extension. If they differ, we
+		 * force user to execute ALTER EXTENSION citus UPDATE. To allow this,
+		 * CREATE/DROP/ALTER extension must be omitted from Citus processing.
+		 */
+		case T_DropStmt:
+		{
+			DropStmt *dropStatement = (DropStmt *) parsetree;
+
+			if (dropStatement->removeType != OBJECT_EXTENSION)
+			{
+				return false;
+			}
+		}
+
+		/* no break, fall through */
+
+		case T_CreateExtensionStmt:
+		case T_AlterExtensionStmt:
+
+		/*
+		 * Transaction statements (e.g. ABORT, COMMIT) can be run in aborted
+		 * transactions in which case a lot of checks cannot be done safely in
+		 * that state. Since we never need to intercept transaction statements,
+		 * skip our checks and immediately fall into standard_ProcessUtility.
+		 */
+		case T_TransactionStmt:
+
+		/*
+		 * Skip processing of variable set statements, to allow changing the
+		 * enable_version_checks GUC during testing.
+		 */
+		case T_VariableSetStmt:
+		{
+			return true;
+		}
+
+		default:
+		{
+			return false;
+		}
+	}
+}
+
+
+/*
+ * IsCitusExtensionStmt returns whether a given utility is a CREATE or ALTER
+ * EXTENSION statement which references the citus extension. This function
+ * returns false for all other inputs.
+ */
+static bool
+IsCitusExtensionStmt(Node *parsetree)
+{
+	char *extensionName = "";
+
+	if (IsA(parsetree, CreateExtensionStmt))
+	{
+		extensionName = ((CreateExtensionStmt *) parsetree)->extname;
+	}
+	else if (IsA(parsetree, AlterExtensionStmt))
+	{
+		extensionName = ((AlterExtensionStmt *) parsetree)->extname;
+	}
+
+	return (strcmp(extensionName, "citus") == 0);
+}
+
+
 /* Is the passed in statement a transmit statement? */
 static bool
 IsTransmitStmt(Node *parsetree)
@@ -1256,6 +1344,83 @@ DeparseVacuumColumnNames(List *columnNameList)
 }
 
 
+/*
+ * ErrorIfUnstableCreateOrAlterExtensionStmt compares CITUS_EXTENSIONVERSION
+ * and version given CREATE/ALTER EXTENSION statement will create/update to. If
+ * they are not same in major or minor version numbers, this function errors
+ * out. It ignores the schema version.
+ */
+static void
+ErrorIfUnstableCreateOrAlterExtensionStmt(Node *parsetree)
+{
+	char *newExtensionVersion = ExtractNewExtensionVersion(parsetree);
+
+	if (newExtensionVersion != NULL)
+	{
+		/*  explicit version provided in CREATE or ALTER EXTENSION UPDATE; verify */
+		if (!MajorVersionsCompatible(newExtensionVersion, CITUS_EXTENSIONVERSION))
+		{
+			ereport(ERROR, (errmsg("specified version incompatible with loaded "
+								   "Citus library"),
+							errdetail("Loaded library requires %s, but %s was specified.",
+									  CITUS_MAJORVERSION, newExtensionVersion),
+							errhint("If a newer library is present, restart the database "
+									"and try the command again.")));
+		}
+	}
+	else
+	{
+		/*
+		 * No version was specified, so PostgreSQL will use the default_version
+		 * from the citus.control file. In case a new default is available, we
+		 * will force a compatibility check of the latest available version.
+		 */
+		availableExtensionVersion = NULL;
+		ErrorIfAvailableVersionMismatch();
+	}
+}
+
+
+/*
+ * ExtractNewExtensionVersion returns the new extension version specified by
+ * a CREATE or ALTER EXTENSION statement. Other inputs are not permitted. This
+ * function returns NULL for statements with no explicit version specified.
+ */
+static char *
+ExtractNewExtensionVersion(Node *parsetree)
+{
+	char *newVersion = NULL;
+	List *optionsList = NIL;
+	ListCell *optionsCell = NULL;
+
+	if (IsA(parsetree, CreateExtensionStmt))
+	{
+		optionsList = ((CreateExtensionStmt *) parsetree)->options;
+	}
+	else if (IsA(parsetree, AlterExtensionStmt))
+	{
+		optionsList = ((AlterExtensionStmt *) parsetree)->options;
+	}
+	else
+	{
+		/* input must be one of the two above types */
+		Assert(false);
+	}
+
+	foreach(optionsCell, optionsList)
+	{
+		DefElem *defElement = (DefElem *) lfirst(optionsCell);
+		if (strncmp(defElement->defname, "new_version", NAMEDATALEN) == 0)
+		{
+			newVersion = strVal(defElement->arg);
+			break;
+		}
+	}
+
+	return newVersion;
+}
+
+
 /*
  * ErrorIfUnsupportedIndexStmt checks if the corresponding index statement is
  * supported for distributed tables and errors out if it is not.
diff --git a/src/backend/distributed/shared_library_init.c b/src/backend/distributed/shared_library_init.c
index 689296b08..c3dcf4e88 100644
--- a/src/backend/distributed/shared_library_init.c
+++ b/src/backend/distributed/shared_library_init.c
@@ -16,6 +16,7 @@
 #include "fmgr.h"
 #include "miscadmin.h"
 
+#include "citus_version.h"
 #include "commands/explain.h"
 #include "executor/executor.h"
 #include "distributed/citus_nodefuncs.h"
@@ -48,6 +49,8 @@
 /* marks shared object as one loadable by the postgres version compiled against */
 PG_MODULE_MAGIC;
 
+static char *CitusVersion = CITUS_VERSION;
+
 void _PG_init(void);
 
 static void CreateRequiredDirectories(void);
@@ -610,6 +613,26 @@ RegisterCitusConfigVariables(void)
 		0,
 		NULL, NULL, NULL);
 
+	DefineCustomStringVariable(
+		"citus.version",
+		gettext_noop("Shows the Citus library version"),
+		NULL,
+		&CitusVersion,
+		CITUS_VERSION,
+		PGC_INTERNAL,
+		0,
+		NULL, NULL, NULL);
+
+	DefineCustomBoolVariable(
+		"citus.enable_version_checks",
+		gettext_noop("Enables version checks during CREATE/ALTER EXTENSION commands"),
+		NULL,
+		&EnableVersionChecks,
+		true,
+		PGC_USERSET,
+		GUC_NO_SHOW_ALL,
+		NULL, NULL, NULL);
+
 	/* warn about config items in the citus namespace that are not registered above */
 	EmitWarningsOnPlaceholders("citus");
 }
diff --git a/src/backend/distributed/utils/metadata_cache.c b/src/backend/distributed/utils/metadata_cache.c
index 2939ade41..275441320 100644
--- a/src/backend/distributed/utils/metadata_cache.c
+++ b/src/backend/distributed/utils/metadata_cache.c
@@ -22,6 +22,7 @@
 #include "catalog/pg_extension.h"
 #include "catalog/pg_namespace.h"
 #include "catalog/pg_type.h"
+#include "citus_version.h"
 #include "commands/extension.h"
 #include "commands/trigger.h"
 #include "distributed/colocation_utils.h"
@@ -35,6 +36,7 @@
 #include "distributed/shardinterval_utils.h"
 #include "distributed/worker_manager.h"
 #include "distributed/worker_protocol.h"
+#include "executor/executor.h"
 #include "parser/parse_func.h"
 #include "utils/builtins.h"
 #include "utils/catcache.h"
@@ -98,6 +100,12 @@ static Oid distTransactionRelationId = InvalidOid;
 static Oid distTransactionGroupIndexId = InvalidOid;
 static Oid extraDataContainerFuncId = InvalidOid;
 
+/* Citus extension version variables */
+bool EnableVersionChecks = true; /* version checks are enabled */
+
+char *availableExtensionVersion = NULL;
+static char *installedExtensionVersion = NULL;
+
 /* Hash table for informations about each partition */
 static HTAB *DistTableCacheHash = NULL;
 
@@ -133,6 +141,9 @@ static bool HasUniformHashDistribution(ShardInterval **shardIntervalArray,
 									   int shardIntervalArrayLength);
 static bool HasUninitializedShardInterval(ShardInterval **sortedShardIntervalArray,
 										  int shardCount);
+static void ErrorIfInstalledVersionMismatch(void);
+static char * AvailableExtensionVersion(void);
+static char * InstalledExtensionVersion(void);
 static void InitializeDistTableCache(void);
 static void InitializeWorkerNodeCache(void);
 static uint32 WorkerNodeHashCode(const void *key, Size keySize);
@@ -927,7 +938,7 @@ bool
 CitusHasBeenLoaded(void)
 {
 	/* recheck presence until citus has been loaded */
-	if (!extensionLoaded)
+	if (!extensionLoaded || creating_extension)
 	{
 		bool extensionPresent = false;
 		bool extensionScriptExecuted = true;
@@ -964,13 +975,286 @@ CitusHasBeenLoaded(void)
 			 * present during early stages of upgrade operation.
 			 */
 			DistPartitionRelationId();
+
+			/*
+			 * We also set installedExtensionVersion to NULL so that it will be re-read
+			 * in case of extension update.
+			 */
+			installedExtensionVersion = NULL;
 		}
 	}
 
+	if (extensionLoaded)
+	{
+		ErrorIfAvailableVersionMismatch();
+		ErrorIfInstalledVersionMismatch();
+	}
+
 	return extensionLoaded;
 }
 
 
+/*
+ * ErrorIfAvailableExtensionVersionMismatch compares CITUS_EXTENSIONVERSION and
+ * currently available version from citus.control file. If they are not same in
+ * major or minor version numbers, this function errors out. It ignores the schema
+ * version.
+ */
+void
+ErrorIfAvailableVersionMismatch(void)
+{
+	char *availableVersion = NULL;
+
+	if (!EnableVersionChecks)
+	{
+		return;
+	}
+
+	availableVersion = AvailableExtensionVersion();
+	if (!MajorVersionsCompatible(availableVersion, CITUS_EXTENSIONVERSION))
+	{
+		ereport(ERROR, (errmsg("loaded Citus library version differs from latest "
+							   "available extension version"),
+						errdetail("Loaded library requires %s, but the latest control "
+								  "file specifies %s.", CITUS_MAJORVERSION,
+								  availableVersion),
+						errhint("Restart the database to load the latest Citus "
+								"library.")));
+	}
+}
+
+
+/*
+ * ErrorIfInstalledVersionMismatch compares CITUS_EXTENSIONVERSION and currently
+ * and catalog version from pg_extemsion catalog table. If they are not same in
+ * major or minor version numbers, this function errors out. It ignores the schema
+ * version.
+ */
+static void
+ErrorIfInstalledVersionMismatch(void)
+{
+	char *installedVersion = NULL;
+
+	if (!EnableVersionChecks)
+	{
+		return;
+	}
+
+	installedVersion = InstalledExtensionVersion();
+	if (!MajorVersionsCompatible(installedVersion, CITUS_EXTENSIONVERSION))
+	{
+		ereport(ERROR, (errmsg("loaded Citus library version differs from installed "
+							   "extension version"),
+						errdetail("Loaded library requires %s, but the installed "
+								  "extension version is %s.", CITUS_MAJORVERSION,
+								  installedVersion),
+						errhint("Run ALTER EXTENSION citus UPDATE and try again.")));
+	}
+}
+
+
+/*
+ * MajorVersionsCompatible compares given two versions. If they are same in major
+ * and minor version numbers, this function returns true. It ignores the schema
+ * version.
+ */
+bool
+MajorVersionsCompatible(char *leftVersion, char *rightVersion)
+{
+	const char schemaVersionSeparator = '-';
+
+	char *leftSeperatorPosition = strchr(leftVersion, schemaVersionSeparator);
+	char *rightSeperatorPosition = strchr(rightVersion, schemaVersionSeparator);
+	int leftComparisionLimit = 0;
+	int rightComparisionLimit = 0;
+
+	if (leftSeperatorPosition != NULL)
+	{
+		leftComparisionLimit = leftSeperatorPosition - leftVersion;
+	}
+	else
+	{
+		leftComparisionLimit = strlen(leftVersion);
+	}
+
+	if (rightSeperatorPosition != NULL)
+	{
+		rightComparisionLimit = rightSeperatorPosition - rightVersion;
+	}
+	else
+	{
+		rightComparisionLimit = strlen(leftVersion);
+	}
+
+	/* we can error out early if hypens are not in the same position */
+	if (leftComparisionLimit != rightComparisionLimit)
+	{
+		return false;
+	}
+
+	return strncmp(leftVersion, rightVersion, leftComparisionLimit) == 0;
+}
+
+
+/*
+ * AvailableExtensionVersion returns the Citus version from citus.control file. It also
+ * saves the result, thus consecutive calls to CitusExtensionAvailableVersion will
+ * not read the citus.control file again.
+ */
+static char *
+AvailableExtensionVersion(void)
+{
+	ReturnSetInfo *extensionsResultSet = NULL;
+	TupleTableSlot *tupleTableSlot = NULL;
+	FunctionCallInfoData *fcinfo = NULL;
+	FmgrInfo *flinfo = NULL;
+	int argumentCount = 0;
+	EState *estate = NULL;
+
+	bool hasTuple = false;
+	bool goForward = true;
+	bool doCopy = false;
+
+	/* if we cached the result before, return it*/
+	if (availableExtensionVersion != NULL)
+	{
+		return availableExtensionVersion;
+	}
+
+	estate = CreateExecutorState();
+	extensionsResultSet = makeNode(ReturnSetInfo);
+	extensionsResultSet->econtext = GetPerTupleExprContext(estate);
+	extensionsResultSet->allowedModes = SFRM_Materialize;
+
+	fcinfo = palloc0(sizeof(FunctionCallInfoData));
+	flinfo = palloc0(sizeof(FmgrInfo));
+
+	fmgr_info(F_PG_AVAILABLE_EXTENSIONS, flinfo);
+	InitFunctionCallInfoData(*fcinfo, flinfo, argumentCount, InvalidOid, NULL,
+							 (Node *) extensionsResultSet);
+
+	/* pg_available_extensions returns result set containing all available extensions */
+	(*pg_available_extensions)(fcinfo);
+
+	tupleTableSlot = MakeSingleTupleTableSlot(extensionsResultSet->setDesc);
+	hasTuple = tuplestore_gettupleslot(extensionsResultSet->setResult, goForward, doCopy,
+									   tupleTableSlot);
+	while (hasTuple)
+	{
+		Datum extensionNameDatum = 0;
+		char *extensionName = NULL;
+		bool isNull = false;
+
+		extensionNameDatum = slot_getattr(tupleTableSlot, 1, &isNull);
+		extensionName = NameStr(*DatumGetName(extensionNameDatum));
+		if (strcmp(extensionName, "citus") == 0)
+		{
+			MemoryContext oldMemoryContext = NULL;
+			Datum availableVersion = slot_getattr(tupleTableSlot, 2, &isNull);
+
+			/* we will cache the result of citus version to prevent catalog access */
+			if (CacheMemoryContext == NULL)
+			{
+				CreateCacheMemoryContext();
+			}
+			oldMemoryContext = MemoryContextSwitchTo(CacheMemoryContext);
+
+			availableExtensionVersion = text_to_cstring(DatumGetTextPP(availableVersion));
+
+			MemoryContextSwitchTo(oldMemoryContext);
+
+			ExecClearTuple(tupleTableSlot);
+			ExecDropSingleTupleTableSlot(tupleTableSlot);
+
+			return availableExtensionVersion;
+		}
+
+		ExecClearTuple(tupleTableSlot);
+		hasTuple = tuplestore_gettupleslot(extensionsResultSet->setResult, goForward,
+										   doCopy, tupleTableSlot);
+	}
+
+	ExecDropSingleTupleTableSlot(tupleTableSlot);
+
+	ereport(ERROR, (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+					errmsg("citus extension is not found")));
+
+	return NULL;
+}
+
+
+/*
+ * InstalledExtensionVersion returns the Citus version in PostgreSQL pg_extension table.
+ * It also saves the result, thus consecutive calls to CitusExtensionCatalogVersion
+ * will not read the catalog tables again.
+ */
+static char *
+InstalledExtensionVersion(void)
+{
+	Relation relation = NULL;
+	SysScanDesc scandesc;
+	ScanKeyData entry[1];
+	HeapTuple extensionTuple = NULL;
+
+	/* if we cached the result before, return it*/
+	if (installedExtensionVersion != NULL)
+	{
+		return installedExtensionVersion;
+	}
+
+	relation = heap_open(ExtensionRelationId, AccessShareLock);
+
+	ScanKeyInit(&entry[0], Anum_pg_extension_extname, BTEqualStrategyNumber, F_NAMEEQ,
+				CStringGetDatum("citus"));
+
+	scandesc = systable_beginscan(relation, ExtensionNameIndexId, true,
+								  NULL, 1, entry);
+
+	extensionTuple = systable_getnext(scandesc);
+
+	/* We assume that there can be at most one matching tuple */
+	if (HeapTupleIsValid(extensionTuple))
+	{
+		MemoryContext oldMemoryContext = NULL;
+		int extensionIndex = Anum_pg_extension_extversion;
+		TupleDesc tupleDescriptor = RelationGetDescr(relation);
+		bool isNull = false;
+
+		Datum installedVersion = heap_getattr(extensionTuple, extensionIndex,
+											  tupleDescriptor, &isNull);
+
+		if (isNull)
+		{
+			ereport(ERROR, (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+							errmsg("citus extension version is null")));
+		}
+
+		/* we will cache the result of citus version to prevent catalog access */
+		if (CacheMemoryContext == NULL)
+		{
+			CreateCacheMemoryContext();
+		}
+
+		oldMemoryContext = MemoryContextSwitchTo(CacheMemoryContext);
+
+		installedExtensionVersion = text_to_cstring(DatumGetTextPP(installedVersion));
+
+		MemoryContextSwitchTo(oldMemoryContext);
+	}
+	else
+	{
+		ereport(ERROR, (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+						errmsg("citus extension is not loaded")));
+	}
+
+	systable_endscan(scandesc);
+
+	heap_close(relation, AccessShareLock);
+
+	return installedExtensionVersion;
+}
+
+
 /* return oid of pg_dist_shard relation */
 Oid
 DistShardRelationId(void)
diff --git a/src/include/.gitignore b/src/include/.gitignore
index 5207873bf..e97125f70 100644
--- a/src/include/.gitignore
+++ b/src/include/.gitignore
@@ -2,3 +2,5 @@
 /stamp-ext-h
 /citus_config.h
 /citus_config.h.in~
+/citus_version.h
+/citus_version.h.in~
diff --git a/src/include/citus_config.h.in b/src/include/citus_config.h.in
index 33da446e7..364d22d47 100644
--- a/src/include/citus_config.h.in
+++ b/src/include/citus_config.h.in
@@ -10,6 +10,18 @@
  */
 
 
+/* Extension version expected by this Citus build */
+#undef CITUS_EXTENSIONVERSION
+
+/* Citus major version as a string */
+#undef CITUS_MAJORVERSION
+
+/* Citus version as a string */
+#undef CITUS_VERSION
+
+/* Citus version as a number */
+#undef CITUS_VERSION_NUM
+
 /* Define to the address where bug reports for this package should be sent. */
 #undef PACKAGE_BUGREPORT
 
diff --git a/src/include/citus_version.h.in b/src/include/citus_version.h.in
new file mode 100644
index 000000000..2367b86fa
--- /dev/null
+++ b/src/include/citus_version.h.in
@@ -0,0 +1,13 @@
+/* This file is created manually */
+
+/* Extension version expected by this Citus build */
+#undef CITUS_EXTENSIONVERSION
+
+/* Citus major version as a string */
+#undef CITUS_MAJORVERSION
+
+/* Citus version as a string */
+#undef CITUS_VERSION
+
+/* Citus version as a number */
+#undef CITUS_VERSION_NUM
diff --git a/src/include/distributed/metadata_cache.h b/src/include/distributed/metadata_cache.h
index abd1861c0..5b87a59a4 100644
--- a/src/include/distributed/metadata_cache.h
+++ b/src/include/distributed/metadata_cache.h
@@ -17,6 +17,8 @@
 #include "distributed/worker_manager.h"
 #include "utils/hsearch.h"
 
+extern bool EnableVersionChecks;
+extern char *availableExtensionVersion;
 
 /*
  * Representation of a table's metadata that is frequently used for
@@ -68,6 +70,8 @@ extern void CitusInvalidateRelcacheByRelid(Oid relationId);
 extern void CitusInvalidateRelcacheByShardId(int64 shardId);
 
 extern bool CitusHasBeenLoaded(void);
+void ErrorIfAvailableVersionMismatch(void);
+bool MajorVersionsCompatible(char *leftVersion, char *rightVersion);
 
 /* access WorkerNodeHash */
 extern HTAB * GetWorkerNodeHash(void);
diff --git a/src/include/distributed/multi_utility.h b/src/include/distributed/multi_utility.h
index 7444c10a1..84ed37443 100644
--- a/src/include/distributed/multi_utility.h
+++ b/src/include/distributed/multi_utility.h
@@ -13,6 +13,7 @@
 #include "tcop/utility.h"
 
 extern bool EnableDDLPropagation;
+extern bool EnableVersionChecks;
 
 /*
  * A DDLJob encapsulates the remote tasks and commands needed to process all or
diff --git a/src/test/regress/expected/multi_extension.out b/src/test/regress/expected/multi_extension.out
index 8655907f8..3daa82f42 100644
--- a/src/test/regress/expected/multi_extension.out
+++ b/src/test/regress/expected/multi_extension.out
@@ -24,7 +24,8 @@ WHERE pgd.refclassid = 'pg_extension'::regclass AND
 -- DROP EXTENSION pre-created by the regression suite
 DROP EXTENSION citus;
 \c
--- Create extension in oldest version, test every upgrade step
+SET citus.enable_version_checks TO 'false';
+-- Create extension in oldest version
 CREATE EXTENSION citus VERSION '5.0';
 ALTER EXTENSION citus UPDATE TO '5.0-1';
 ALTER EXTENSION citus UPDATE TO '5.0-2';
@@ -77,6 +78,13 @@ ALTER EXTENSION citus UPDATE TO '6.1-16';
 ALTER EXTENSION citus UPDATE TO '6.1-17';
 ALTER EXTENSION citus UPDATE TO '6.2-1';
 ALTER EXTENSION citus UPDATE TO '6.2-2';
+-- show running version
+SHOW citus.version;
+ citus.version 
+---------------
+ 6.2devel
+(1 row)
+
 -- ensure no objects were created outside pg_catalog
 SELECT COUNT(*)
 FROM pg_depend AS pgd,
@@ -91,7 +99,13 @@ WHERE pgd.refclassid = 'pg_extension'::regclass AND
      0
 (1 row)
 
--- drop extension an re-create in newest version
+-- see incompatible version errors out
+RESET citus.enable_version_checks;
 DROP EXTENSION citus;
+CREATE EXTENSION citus VERSION '5.0';
+ERROR:  specified version incompatible with loaded Citus library
+DETAIL:  Loaded library requires 6.2, but 5.0 was specified.
+HINT:  If a newer library is present, restart the database and try the command again.
+-- re-create in newest version
 \c
 CREATE EXTENSION citus;
diff --git a/src/test/regress/sql/multi_extension.sql b/src/test/regress/sql/multi_extension.sql
index d1a1ff559..0be9c5096 100644
--- a/src/test/regress/sql/multi_extension.sql
+++ b/src/test/regress/sql/multi_extension.sql
@@ -24,7 +24,9 @@ WHERE pgd.refclassid = 'pg_extension'::regclass AND
 DROP EXTENSION citus;
 \c
 
--- Create extension in oldest version, test every upgrade step
+SET citus.enable_version_checks TO 'false';
+
+-- Create extension in oldest version
 CREATE EXTENSION citus VERSION '5.0';
 ALTER EXTENSION citus UPDATE TO '5.0-1';
 ALTER EXTENSION citus UPDATE TO '5.0-2';
@@ -78,6 +80,9 @@ ALTER EXTENSION citus UPDATE TO '6.1-17';
 ALTER EXTENSION citus UPDATE TO '6.2-1';
 ALTER EXTENSION citus UPDATE TO '6.2-2';
 
+-- show running version
+SHOW citus.version;
+
 -- ensure no objects were created outside pg_catalog
 SELECT COUNT(*)
 FROM pg_depend AS pgd,
@@ -88,7 +93,11 @@ WHERE pgd.refclassid = 'pg_extension'::regclass AND
 	  pge.extname    = 'citus' AND
 	  pgio.schema    NOT IN ('pg_catalog', 'citus');
 
--- drop extension an re-create in newest version
+-- see incompatible version errors out
+RESET citus.enable_version_checks;
 DROP EXTENSION citus;
+CREATE EXTENSION citus VERSION '5.0';
+
+-- re-create in newest version
 \c
 CREATE EXTENSION citus;