v3-0001-Add-option-to-use-ICU-as-global-collation-provide.patch

From 4eb9fbac238c1abf481fa43431ecc22e782a5290 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Thu, 30 Dec 2021 12:47:24 +0100
Subject: [PATCH v3] Add option to use ICU as global collation provider

This adds the option to use ICU as the default collation provider for
either the whole cluster or a database.  New options for initdb,
createdb, and CREATE DATABASE are used to select this.

Discussion: https://www.postgresql.org/message-id/flat/5e756dd6-0e91-d778-96fd-b1bcb06c161a%402ndquadrant.com
---
 doc/src/sgml/catalogs.sgml                    |  13 +-
 doc/src/sgml/ref/create_database.sgml         |  16 ++
 doc/src/sgml/ref/createdb.sgml                |   9 +
 doc/src/sgml/ref/initdb.sgml                  |  23 ++
 src/backend/access/hash/hashfunc.c            |  18 +-
 src/backend/catalog/pg_collation.c            |  24 +-
 src/backend/commands/collationcmds.c          | 120 +++++++---
 src/backend/commands/dbcommands.c             |  93 ++++++--
 src/backend/regex/regc_pg_locale.c            |   7 +-
 src/backend/utils/adt/formatting.c            |   6 +
 src/backend/utils/adt/like.c                  |  20 +-
 src/backend/utils/adt/like_support.c          |   2 +
 src/backend/utils/adt/pg_locale.c             | 223 +++++++++++-------
 src/backend/utils/adt/varchar.c               |  22 +-
 src/backend/utils/adt/varlena.c               |  26 +-
 src/backend/utils/init/postinit.c             |  37 ++-
 src/bin/initdb/Makefile                       |   2 +
 src/bin/initdb/initdb.c                       |  62 ++++-
 src/bin/initdb/t/001_initdb.pl                |  18 +-
 src/bin/pg_dump/pg_dump.c                     |  16 ++
 src/bin/psql/describe.c                       |  23 +-
 src/bin/psql/tab-complete.c                   |   2 +-
 src/bin/scripts/Makefile                      |   2 +
 src/bin/scripts/createdb.c                    |   9 +
 src/bin/scripts/t/020_createdb.pl             |  20 +-
 src/include/catalog/pg_collation.dat          |   3 +-
 src/include/catalog/pg_collation.h            |   6 +-
 src/include/catalog/pg_database.dat           |   2 +-
 src/include/catalog/pg_database.h             |  16 +-
 src/include/utils/pg_locale.h                 |   6 +
 .../regress/expected/collate.icu.utf8.out     |  10 +-
 src/test/regress/sql/collate.icu.utf8.sql     |   8 +-
 32 files changed, 665 insertions(+), 199 deletions(-)

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 03e2537b07..89e7279030 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -2368,7 +2368,7 @@ <title><structname>pg_collation</structname> Columns</title>
 
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>collcollate</structfield> <type>name</type>
+       <structfield>collcollate</structfield> <type>text</type>
       </para>
       <para>
        <symbol>LC_COLLATE</symbol> for this collation object
@@ -2377,13 +2377,22 @@ <title><structname>pg_collation</structname> Columns</title>
 
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>collctype</structfield> <type>name</type>
+       <structfield>collctype</structfield> <type>text</type>
       </para>
       <para>
        <symbol>LC_CTYPE</symbol> for this collation object
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>collicucoll</structfield> <type>text</type>
+      </para>
+      <para>
+       ICU collation string
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>collversion</structfield> <type>text</type>
diff --git a/doc/src/sgml/ref/create_database.sgml b/doc/src/sgml/ref/create_database.sgml
index 41cb4068ec..7374a9fad5 100644
--- a/doc/src/sgml/ref/create_database.sgml
+++ b/doc/src/sgml/ref/create_database.sgml
@@ -28,6 +28,7 @@
            [ LOCALE [=] <replaceable class="parameter">locale</replaceable> ]
            [ LC_COLLATE [=] <replaceable class="parameter">lc_collate</replaceable> ]
            [ LC_CTYPE [=] <replaceable class="parameter">lc_ctype</replaceable> ]
+           [ COLLATION_PROVIDER [=] <replaceable class="parameter">collation_provider</replaceable> ]
            [ TABLESPACE [=] <replaceable class="parameter">tablespace_name</replaceable> ]
            [ ALLOW_CONNECTIONS [=] <replaceable class="parameter">allowconn</replaceable> ]
            [ CONNECTION LIMIT [=] <replaceable class="parameter">connlimit</replaceable> ]
@@ -157,6 +158,21 @@ <title>Parameters</title>
        </para>
       </listitem>
      </varlistentry>
+
+     <varlistentry>
+      <term><replaceable>collation_provider</replaceable></term>
+
+      <listitem>
+       <para>
+        Specifies the provider to use for the default collation in this
+        database.  Possible values are:
+        <literal>icu</literal>,<indexterm><primary>ICU</primary></indexterm>
+        <literal>libc</literal>.  <literal>libc</literal> is the default.  The
+        available choices depend on the operating system and build options.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><replaceable class="parameter">tablespace_name</replaceable></term>
       <listitem>
diff --git a/doc/src/sgml/ref/createdb.sgml b/doc/src/sgml/ref/createdb.sgml
index 86473455c9..4b07363fcc 100644
--- a/doc/src/sgml/ref/createdb.sgml
+++ b/doc/src/sgml/ref/createdb.sgml
@@ -83,6 +83,15 @@ <title>Options</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--collation-provider={<literal>libc</literal>|<literal>icu</literal>}</option></term>
+      <listitem>
+       <para>
+        Specifies the collation provider for the database's default collation.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-D <replaceable class="parameter">tablespace</replaceable></option></term>
       <term><option>--tablespace=<replaceable class="parameter">tablespace</replaceable></option></term>
diff --git a/doc/src/sgml/ref/initdb.sgml b/doc/src/sgml/ref/initdb.sgml
index 8f71c7c962..77618d9a7a 100644
--- a/doc/src/sgml/ref/initdb.sgml
+++ b/doc/src/sgml/ref/initdb.sgml
@@ -166,6 +166,18 @@ <title>Options</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--collation-provider={<literal>libc</literal>|<literal>icu</literal>}</option></term>
+      <listitem>
+       <para>
+        This option sets the collation provider for databases created in the
+        new cluster.  It can be overridden in the <command>CREATE
+        DATABASE</command> command when new databases are subsequently
+        created.  The default is <literal>libc</literal>.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-D <replaceable class="parameter">directory</replaceable></option></term>
       <term><option>--pgdata=<replaceable class="parameter">directory</replaceable></option></term>
@@ -210,6 +222,17 @@ <title>Options</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--icu-locale=<replaceable>locale</replaceable></option></term>
+      <listitem>
+       <para>
+        Specifies the ICU locale if the ICU collation provider is used.  If
+        this is not specified, the value from the <option>--locale</option>
+        option is used.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="app-initdb-data-checksums" xreflabel="data checksums">
       <term><option>-k</option></term>
       <term><option>--data-checksums</option></term>
diff --git a/src/backend/access/hash/hashfunc.c b/src/backend/access/hash/hashfunc.c
index 242333920e..6c29816193 100644
--- a/src/backend/access/hash/hashfunc.c
+++ b/src/backend/access/hash/hashfunc.c
@@ -278,8 +278,13 @@ hashtext(PG_FUNCTION_ARGS)
 				 errmsg("could not determine which collation to use for string hashing"),
 				 errhint("Use the COLLATE clause to set the collation explicitly.")));
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
+	}
 
 	if (!mylocale || mylocale->deterministic)
 	{
@@ -334,8 +339,13 @@ hashtextextended(PG_FUNCTION_ARGS)
 				 errmsg("could not determine which collation to use for string hashing"),
 				 errhint("Use the COLLATE clause to set the collation explicitly.")));
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
+	}
 
 	if (!mylocale || mylocale->deterministic)
 	{
diff --git a/src/backend/catalog/pg_collation.c b/src/backend/catalog/pg_collation.c
index 19068b652a..c3365e99c3 100644
--- a/src/backend/catalog/pg_collation.c
+++ b/src/backend/catalog/pg_collation.c
@@ -49,6 +49,7 @@ CollationCreate(const char *collname, Oid collnamespace,
 				bool collisdeterministic,
 				int32 collencoding,
 				const char *collcollate, const char *collctype,
+				const char *collicucoll,
 				const char *collversion,
 				bool if_not_exists,
 				bool quiet)
@@ -58,9 +59,7 @@ CollationCreate(const char *collname, Oid collnamespace,
 	HeapTuple	tup;
 	Datum		values[Natts_pg_collation];
 	bool		nulls[Natts_pg_collation];
-	NameData	name_name,
-				name_collate,
-				name_ctype;
+	NameData	name_name;
 	Oid			oid;
 	ObjectAddress myself,
 				referenced;
@@ -68,8 +67,7 @@ CollationCreate(const char *collname, Oid collnamespace,
 	AssertArg(collname);
 	AssertArg(collnamespace);
 	AssertArg(collowner);
-	AssertArg(collcollate);
-	AssertArg(collctype);
+	AssertArg((collcollate && collctype) || collicucoll);
 
 	/*
 	 * Make sure there is no existing collation of same name & encoding.
@@ -163,10 +161,18 @@ CollationCreate(const char *collname, Oid collnamespace,
 	values[Anum_pg_collation_collprovider - 1] = CharGetDatum(collprovider);
 	values[Anum_pg_collation_collisdeterministic - 1] = BoolGetDatum(collisdeterministic);
 	values[Anum_pg_collation_collencoding - 1] = Int32GetDatum(collencoding);
-	namestrcpy(&name_collate, collcollate);
-	values[Anum_pg_collation_collcollate - 1] = NameGetDatum(&name_collate);
-	namestrcpy(&name_ctype, collctype);
-	values[Anum_pg_collation_collctype - 1] = NameGetDatum(&name_ctype);
+	if (collcollate)
+		values[Anum_pg_collation_collcollate - 1] = CStringGetTextDatum(collcollate);
+	else
+		nulls[Anum_pg_collation_collcollate - 1] = true;
+	if (collctype)
+		values[Anum_pg_collation_collctype - 1] = CStringGetTextDatum(collctype);
+	else
+		nulls[Anum_pg_collation_collctype - 1] = true;
+	if (collicucoll)
+		values[Anum_pg_collation_collicucoll - 1] = CStringGetTextDatum(collicucoll);
+	else
+		nulls[Anum_pg_collation_collicucoll - 1] = true;
 	if (collversion)
 		values[Anum_pg_collation_collversion - 1] = CStringGetTextDatum(collversion);
 	else
diff --git a/src/backend/commands/collationcmds.c b/src/backend/commands/collationcmds.c
index 53fc579f37..7dd125705b 100644
--- a/src/backend/commands/collationcmds.c
+++ b/src/backend/commands/collationcmds.c
@@ -65,6 +65,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 	DefElem    *versionEl = NULL;
 	char	   *collcollate = NULL;
 	char	   *collctype = NULL;
+	char	   *collicucoll = NULL;
 	char	   *collproviderstr = NULL;
 	bool		collisdeterministic = true;
 	int			collencoding = 0;
@@ -129,18 +130,36 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 	{
 		Oid			collid;
 		HeapTuple	tp;
+		Datum		datum;
+		bool		isnull;
 
 		collid = get_collation_oid(defGetQualifiedName(fromEl), false);
 		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(collid));
 		if (!HeapTupleIsValid(tp))
 			elog(ERROR, "cache lookup failed for collation %u", collid);
 
-		collcollate = pstrdup(NameStr(((Form_pg_collation) GETSTRUCT(tp))->collcollate));
-		collctype = pstrdup(NameStr(((Form_pg_collation) GETSTRUCT(tp))->collctype));
 		collprovider = ((Form_pg_collation) GETSTRUCT(tp))->collprovider;
 		collisdeterministic = ((Form_pg_collation) GETSTRUCT(tp))->collisdeterministic;
 		collencoding = ((Form_pg_collation) GETSTRUCT(tp))->collencoding;
 
+		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
+		if (!isnull)
+			collcollate = TextDatumGetCString(datum);
+		else
+			collcollate = NULL;
+
+		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
+		if (!isnull)
+			collctype = TextDatumGetCString(datum);
+		else
+			collctype = NULL;
+
+		datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collicucoll, &isnull);
+		if (!isnull)
+			collicucoll = TextDatumGetCString(datum);
+		else
+			collicucoll = NULL;
+
 		ReleaseSysCache(tp);
 
 		/*
@@ -156,18 +175,6 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 					 errmsg("collation \"default\" cannot be copied")));
 	}
 
-	if (localeEl)
-	{
-		collcollate = defGetString(localeEl);
-		collctype = defGetString(localeEl);
-	}
-
-	if (lccollateEl)
-		collcollate = defGetString(lccollateEl);
-
-	if (lcctypeEl)
-		collctype = defGetString(lcctypeEl);
-
 	if (providerEl)
 		collproviderstr = defGetString(providerEl);
 
@@ -192,15 +199,43 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 	else if (!fromEl)
 		collprovider = COLLPROVIDER_LIBC;
 
-	if (!collcollate)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-				 errmsg("parameter \"lc_collate\" must be specified")));
+	if (localeEl)
+	{
+		if (collprovider == COLLPROVIDER_LIBC)
+		{
+			collcollate = defGetString(localeEl);
+			collctype = defGetString(localeEl);
+		}
+		else
+			collicucoll = defGetString(localeEl);
+	}
 
-	if (!collctype)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-				 errmsg("parameter \"lc_ctype\" must be specified")));
+	if (lccollateEl)
+		collcollate = defGetString(lccollateEl);
+
+	if (lcctypeEl)
+		collctype = defGetString(lcctypeEl);
+
+	if (collprovider == COLLPROVIDER_LIBC)
+	{
+		if (!collcollate)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("parameter \"lc_collate\" must be specified")));
+
+		if (!collctype)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("parameter \"lc_ctype\" must be specified")));
+	}
+
+	if (collprovider == COLLPROVIDER_ICU)
+	{
+		if (!collicucoll)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("parameter \"locale\" must be specified")));
+	}
 
 	/*
 	 * Nondeterministic collations are currently only supported with ICU
@@ -243,7 +278,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 	}
 
 	if (!collversion)
-		collversion = get_collation_actual_version(collprovider, collcollate);
+		collversion = get_collation_actual_version(collprovider, collprovider == COLLPROVIDER_ICU ? collicucoll : collcollate);
 
 	newoid = CollationCreate(collName,
 							 collNamespace,
@@ -253,6 +288,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 							 collencoding,
 							 collcollate,
 							 collctype,
+							 collicucoll,
 							 collversion,
 							 if_not_exists,
 							 false);	/* not quiet */
@@ -336,7 +372,13 @@ AlterCollation(AlterCollationStmt *stmt)
 								  &isnull);
 	oldversion = isnull ? NULL : TextDatumGetCString(collversion);
 
-	newversion = get_collation_actual_version(collForm->collprovider, NameStr(collForm->collcollate));
+	{
+		Datum	datum;
+
+		datum = SysCacheGetAttr(COLLOID, tup, collForm->collprovider == COLLPROVIDER_ICU ? Anum_pg_collation_collicucoll : Anum_pg_collation_collcollate, &isnull);
+		Assert(!isnull);
+		newversion = get_collation_actual_version(collForm->collprovider, TextDatumGetCString(datum));
+	}
 
 	/* cannot change from NULL to non-NULL or vice versa */
 	if ((!oldversion && newversion) || (oldversion && !newversion))
@@ -383,8 +425,9 @@ pg_collation_actual_version(PG_FUNCTION_ARGS)
 {
 	Oid			collid = PG_GETARG_OID(0);
 	HeapTuple	tp;
-	char	   *collcollate;
 	char		collprovider;
+	Datum		datum;
+	bool		isnull;
 	char	   *version;
 
 	tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(collid));
@@ -393,12 +436,19 @@ pg_collation_actual_version(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_UNDEFINED_OBJECT),
 				 errmsg("collation with OID %u does not exist", collid)));
 
-	collcollate = pstrdup(NameStr(((Form_pg_collation) GETSTRUCT(tp))->collcollate));
 	collprovider = ((Form_pg_collation) GETSTRUCT(tp))->collprovider;
 
-	ReleaseSysCache(tp);
+	if (collprovider != COLLPROVIDER_DEFAULT)
+	{
+		datum = SysCacheGetAttr(COLLOID, tp, collprovider == COLLPROVIDER_ICU ? Anum_pg_collation_collicucoll : Anum_pg_collation_collcollate, &isnull);
+		Assert(!isnull);
+
+		version = get_collation_actual_version(collprovider, TextDatumGetCString(datum));
+	}
+	else
+		version = NULL;
 
-	version = get_collation_actual_version(collprovider, collcollate);
+	ReleaseSysCache(tp);
 
 	if (version)
 		PG_RETURN_TEXT_P(cstring_to_text(version));
@@ -623,7 +673,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 			 */
 			collid = CollationCreate(localebuf, nspid, GetUserId(),
 									 COLLPROVIDER_LIBC, true, enc,
-									 localebuf, localebuf,
+									 localebuf, localebuf, NULL,
 									 get_collation_actual_version(COLLPROVIDER_LIBC, localebuf),
 									 true, true);
 			if (OidIsValid(collid))
@@ -684,7 +734,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 
 			collid = CollationCreate(alias, nspid, GetUserId(),
 									 COLLPROVIDER_LIBC, true, enc,
-									 locale, locale,
+									 locale, locale, NULL,
 									 get_collation_actual_version(COLLPROVIDER_LIBC, locale),
 									 true, true);
 			if (OidIsValid(collid))
@@ -725,7 +775,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 			const char *name;
 			char	   *langtag;
 			char	   *icucomment;
-			const char *collcollate;
+			const char *icucollstr;
 			Oid			collid;
 
 			if (i == -1)
@@ -734,20 +784,20 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 				name = uloc_getAvailable(i);
 
 			langtag = get_icu_language_tag(name);
-			collcollate = U_ICU_VERSION_MAJOR_NUM >= 54 ? langtag : name;
+			icucollstr = U_ICU_VERSION_MAJOR_NUM >= 54 ? langtag : name;
 
 			/*
 			 * Be paranoid about not allowing any non-ASCII strings into
 			 * pg_collation
 			 */
-			if (!pg_is_ascii(langtag) || !pg_is_ascii(collcollate))
+			if (!pg_is_ascii(langtag) || !pg_is_ascii(icucollstr))
 				continue;
 
 			collid = CollationCreate(psprintf("%s-x-icu", langtag),
 									 nspid, GetUserId(),
 									 COLLPROVIDER_ICU, true, -1,
-									 collcollate, collcollate,
-									 get_collation_actual_version(COLLPROVIDER_ICU, collcollate),
+									 NULL, NULL, icucollstr,
+									 get_collation_actual_version(COLLPROVIDER_ICU, icucollstr),
 									 true, true);
 			if (OidIsValid(collid))
 			{
diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index 029fab48df..7928790cc9 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -36,6 +36,7 @@
 #include "catalog/indexing.h"
 #include "catalog/objectaccess.h"
 #include "catalog/pg_authid.h"
+#include "catalog/pg_collation.h"
 #include "catalog/pg_database.h"
 #include "catalog/pg_db_role_setting.h"
 #include "catalog/pg_subscription.h"
@@ -86,7 +87,8 @@ static bool get_db_info(const char *name, LOCKMODE lockmode,
 						int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP,
 						Oid *dbLastSysOidP, TransactionId *dbFrozenXidP,
 						MultiXactId *dbMinMultiP,
-						Oid *dbTablespace, char **dbCollate, char **dbCtype);
+						Oid *dbTablespace, char **dbCollate, char **dbCtype, char **dbIcucoll,
+						char *dbCollProvider);
 static bool have_createdb_privilege(void);
 static void remove_dbtablespaces(Oid db_id);
 static bool check_db_file_conflict(Oid db_id);
@@ -106,6 +108,8 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	int			src_encoding = -1;
 	char	   *src_collate = NULL;
 	char	   *src_ctype = NULL;
+	char	   *src_icucoll = NULL;
+	char		src_collprovider;
 	bool		src_istemplate;
 	bool		src_allowconn;
 	Oid			src_lastsysoid = InvalidOid;
@@ -127,6 +131,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	DefElem    *dlocale = NULL;
 	DefElem    *dcollate = NULL;
 	DefElem    *dctype = NULL;
+	DefElem	   *dcollprovider = NULL;
 	DefElem    *distemplate = NULL;
 	DefElem    *dallowconnections = NULL;
 	DefElem    *dconnlimit = NULL;
@@ -135,6 +140,8 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	const char *dbtemplate = NULL;
 	char	   *dbcollate = NULL;
 	char	   *dbctype = NULL;
+	char	   *dbicucoll = NULL;
+	char		dbcollprovider = '\0';
 	char	   *canonname;
 	int			encoding = -1;
 	bool		dbistemplate = false;
@@ -191,6 +198,15 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 				errorConflictingDefElem(defel, pstate);
 			dctype = defel;
 		}
+		else if (strcmp(defel->defname, "collation_provider") == 0)
+		{
+			if (dcollprovider)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options"),
+						 parser_errposition(pstate, defel->location)));
+			dcollprovider = defel;
+		}
 		else if (strcmp(defel->defname, "is_template") == 0)
 		{
 			if (distemplate)
@@ -224,12 +240,6 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 					 parser_errposition(pstate, defel->location)));
 	}
 
-	if (dlocale && (dcollate || dctype))
-		ereport(ERROR,
-				(errcode(ERRCODE_SYNTAX_ERROR),
-				 errmsg("conflicting or redundant options"),
-				 errdetail("LOCALE cannot be specified together with LC_COLLATE or LC_CTYPE.")));
-
 	if (downer && downer->arg)
 		dbowner = defGetString(downer);
 	if (dtemplate && dtemplate->arg)
@@ -266,11 +276,29 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	{
 		dbcollate = defGetString(dlocale);
 		dbctype = defGetString(dlocale);
+		dbicucoll = defGetString(dlocale);
 	}
 	if (dcollate && dcollate->arg)
 		dbcollate = defGetString(dcollate);
 	if (dctype && dctype->arg)
 		dbctype = defGetString(dctype);
+	if (dcollprovider && dcollprovider->arg)
+	{
+		char	   *collproviderstr = defGetString(dcollprovider);
+
+#ifdef USE_ICU
+		if (pg_strcasecmp(collproviderstr, "icu") == 0)
+			dbcollprovider = COLLPROVIDER_ICU;
+		else
+#endif
+		if (pg_strcasecmp(collproviderstr, "libc") == 0)
+			dbcollprovider = COLLPROVIDER_LIBC;
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("unrecognized collation provider: %s",
+							collproviderstr)));
+	}
 	if (distemplate && distemplate->arg)
 		dbistemplate = defGetBoolean(distemplate);
 	if (dallowconnections && dallowconnections->arg)
@@ -320,7 +348,7 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 					 &src_dboid, &src_owner, &src_encoding,
 					 &src_istemplate, &src_allowconn, &src_lastsysoid,
 					 &src_frozenxid, &src_minmxid, &src_deftablespace,
-					 &src_collate, &src_ctype))
+					 &src_collate, &src_ctype, &src_icucoll, &src_collprovider))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("template database \"%s\" does not exist",
@@ -346,6 +374,10 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		dbcollate = src_collate;
 	if (dbctype == NULL)
 		dbctype = src_ctype;
+	if (dbicucoll == NULL)
+		dbicucoll = src_icucoll;
+	if (dbcollprovider == '\0')
+		dbcollprovider = src_collprovider;
 
 	/* Some encodings are client only */
 	if (!PG_VALID_BE_ENCODING(encoding))
@@ -525,10 +557,13 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		DirectFunctionCall1(namein, CStringGetDatum(dbname));
 	new_record[Anum_pg_database_datdba - 1] = ObjectIdGetDatum(datdba);
 	new_record[Anum_pg_database_encoding - 1] = Int32GetDatum(encoding);
-	new_record[Anum_pg_database_datcollate - 1] =
-		DirectFunctionCall1(namein, CStringGetDatum(dbcollate));
-	new_record[Anum_pg_database_datctype - 1] =
-		DirectFunctionCall1(namein, CStringGetDatum(dbctype));
+	new_record[Anum_pg_database_datcollate - 1] = CStringGetTextDatum(dbcollate);
+	new_record[Anum_pg_database_datctype - 1] = CStringGetTextDatum(dbctype);
+	if (dbicucoll)
+		new_record[Anum_pg_database_daticucoll - 1] = CStringGetTextDatum(dbicucoll);
+	else
+		new_record_nulls[Anum_pg_database_daticucoll] = true;
+	new_record[Anum_pg_database_datcollprovider - 1] = CharGetDatum(dbcollprovider);
 	new_record[Anum_pg_database_datistemplate - 1] = BoolGetDatum(dbistemplate);
 	new_record[Anum_pg_database_datallowconn - 1] = BoolGetDatum(dballowconnections);
 	new_record[Anum_pg_database_datconnlimit - 1] = Int32GetDatum(dbconnlimit);
@@ -802,7 +837,7 @@ dropdb(const char *dbname, bool missing_ok, bool force)
 	pgdbrel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(dbname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 &db_istemplate, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
+					 &db_istemplate, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
 	{
 		if (!missing_ok)
 		{
@@ -1001,7 +1036,7 @@ RenameDatabase(const char *oldname, const char *newname)
 	rel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(oldname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
+					 NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("database \"%s\" does not exist", oldname)));
@@ -1114,7 +1149,7 @@ movedb(const char *dbname, const char *tblspcname)
 	pgdbrel = table_open(DatabaseRelationId, RowExclusiveLock);
 
 	if (!get_db_info(dbname, AccessExclusiveLock, &db_id, NULL, NULL,
-					 NULL, NULL, NULL, NULL, NULL, &src_tblspcoid, NULL, NULL))
+					 NULL, NULL, NULL, NULL, NULL, &src_tblspcoid, NULL, NULL, NULL, NULL))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_DATABASE),
 				 errmsg("database \"%s\" does not exist", dbname)));
@@ -1759,7 +1794,8 @@ get_db_info(const char *name, LOCKMODE lockmode,
 			int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP,
 			Oid *dbLastSysOidP, TransactionId *dbFrozenXidP,
 			MultiXactId *dbMinMultiP,
-			Oid *dbTablespace, char **dbCollate, char **dbCtype)
+			Oid *dbTablespace, char **dbCollate, char **dbCtype, char **dbIcucoll,
+			char *dbCollProvider)
 {
 	bool		result = false;
 	Relation	relation;
@@ -1824,6 +1860,9 @@ get_db_info(const char *name, LOCKMODE lockmode,
 
 			if (strcmp(name, NameStr(dbform->datname)) == 0)
 			{
+				Datum		datum;
+				bool		isnull;
+
 				/* oid of the database */
 				if (dbIdP)
 					*dbIdP = dbOid;
@@ -1852,10 +1891,28 @@ get_db_info(const char *name, LOCKMODE lockmode,
 				if (dbTablespace)
 					*dbTablespace = dbform->dattablespace;
 				/* default locale settings for this database */
+				if (dbCollProvider)
+					*dbCollProvider = dbform->datcollprovider;
 				if (dbCollate)
-					*dbCollate = pstrdup(NameStr(dbform->datcollate));
+				{
+					datum = SysCacheGetAttr(DATABASEOID, tuple, Anum_pg_database_datcollate, &isnull);
+					Assert(!isnull);
+					*dbCollate = TextDatumGetCString(datum);
+				}
 				if (dbCtype)
-					*dbCtype = pstrdup(NameStr(dbform->datctype));
+				{
+					datum = SysCacheGetAttr(DATABASEOID, tuple, Anum_pg_database_datctype, &isnull);
+					Assert(!isnull);
+					*dbCtype = TextDatumGetCString(datum);
+				}
+				if (dbIcucoll)
+				{
+					datum = SysCacheGetAttr(DATABASEOID, tuple, Anum_pg_database_daticucoll, &isnull);
+					if (isnull)
+						*dbIcucoll = NULL;
+					else
+						*dbIcucoll = TextDatumGetCString(datum);
+				}
 				ReleaseSysCache(tuple);
 				result = true;
 				break;
diff --git a/src/backend/regex/regc_pg_locale.c b/src/backend/regex/regc_pg_locale.c
index bbbd61c604..3fe0f1c386 100644
--- a/src/backend/regex/regc_pg_locale.c
+++ b/src/backend/regex/regc_pg_locale.c
@@ -241,7 +241,12 @@ pg_set_regex_collation(Oid collation)
 	else
 	{
 		if (collation == DEFAULT_COLLATION_OID)
-			pg_regex_locale = 0;
+		{
+			if (default_locale.provider == COLLPROVIDER_ICU)
+				pg_regex_locale = &default_locale;
+			else
+				pg_regex_locale = 0;
+		}
 		else if (OidIsValid(collation))
 		{
 			/*
diff --git a/src/backend/utils/adt/formatting.c b/src/backend/utils/adt/formatting.c
index 419469fab5..320047fbd0 100644
--- a/src/backend/utils/adt/formatting.c
+++ b/src/backend/utils/adt/formatting.c
@@ -1666,6 +1666,8 @@ str_tolower(const char *buff, size_t nbytes, Oid collid)
 			}
 			mylocale = pg_newlocale_from_collation(collid);
 		}
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
 
 #ifdef USE_ICU
 		if (mylocale && mylocale->provider == COLLPROVIDER_ICU)
@@ -1790,6 +1792,8 @@ str_toupper(const char *buff, size_t nbytes, Oid collid)
 			}
 			mylocale = pg_newlocale_from_collation(collid);
 		}
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
 
 #ifdef USE_ICU
 		if (mylocale && mylocale->provider == COLLPROVIDER_ICU)
@@ -1915,6 +1919,8 @@ str_initcap(const char *buff, size_t nbytes, Oid collid)
 			}
 			mylocale = pg_newlocale_from_collation(collid);
 		}
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
 
 #ifdef USE_ICU
 		if (mylocale && mylocale->provider == COLLPROVIDER_ICU)
diff --git a/src/backend/utils/adt/like.c b/src/backend/utils/adt/like.c
index eed183cd0d..85a668fa36 100644
--- a/src/backend/utils/adt/like.c
+++ b/src/backend/utils/adt/like.c
@@ -150,9 +150,14 @@ SB_lower_char(unsigned char c, pg_locale_t locale, bool locale_is_c)
 static inline int
 GenericMatchText(const char *s, int slen, const char *p, int plen, Oid collation)
 {
-	if (collation && !lc_ctype_is_c(collation) && collation != DEFAULT_COLLATION_OID)
+	if (collation && !lc_ctype_is_c(collation))
 	{
-		pg_locale_t locale = pg_newlocale_from_collation(collation);
+		pg_locale_t locale = 0;
+
+		if (collation != DEFAULT_COLLATION_OID)
+			locale = pg_newlocale_from_collation(collation);
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			locale = &default_locale;
 
 		if (locale && !locale->deterministic)
 			ereport(ERROR,
@@ -195,11 +200,14 @@ Generic_Text_IC_like(text *str, text *pat, Oid collation)
 		}
 		locale = pg_newlocale_from_collation(collation);
 
-		if (locale && !locale->deterministic)
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("nondeterministic collations are not supported for ILIKE")));
 	}
+	else if (default_locale.provider == COLLPROVIDER_ICU)
+		locale = &default_locale;
+
+	if (locale && !locale->deterministic)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("nondeterministic collations are not supported for ILIKE")));
 
 	/*
 	 * For efficiency reasons, in the single byte case we don't call lower()
diff --git a/src/backend/utils/adt/like_support.c b/src/backend/utils/adt/like_support.c
index 988568825e..6b82ad1d43 100644
--- a/src/backend/utils/adt/like_support.c
+++ b/src/backend/utils/adt/like_support.c
@@ -1030,6 +1030,8 @@ like_fixed_prefix(Const *patt_const, bool case_insensitive, Oid collation,
 			}
 			locale = pg_newlocale_from_collation(collation);
 		}
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			locale = &default_locale;
 	}
 
 	if (typeid != BYTEAOID)
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index cc2ab95535..8d32bc68d8 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1289,21 +1289,36 @@ lookup_collation_cache(Oid collation, bool set_flags)
 		/* Attempt to set the flags */
 		HeapTuple	tp;
 		Form_pg_collation collform;
-		const char *collcollate;
-		const char *collctype;
 
 		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(collation));
 		if (!HeapTupleIsValid(tp))
 			elog(ERROR, "cache lookup failed for collation %u", collation);
 		collform = (Form_pg_collation) GETSTRUCT(tp);
 
-		collcollate = NameStr(collform->collcollate);
-		collctype = NameStr(collform->collctype);
-
-		cache_entry->collate_is_c = ((strcmp(collcollate, "C") == 0) ||
-									 (strcmp(collcollate, "POSIX") == 0));
-		cache_entry->ctype_is_c = ((strcmp(collctype, "C") == 0) ||
-								   (strcmp(collctype, "POSIX") == 0));
+		if (collform->collprovider == COLLPROVIDER_LIBC)
+		{
+			Datum		datum;
+			bool		isnull;
+			const char *collcollate;
+			const char *collctype;
+
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
+			Assert(!isnull);
+			collcollate = TextDatumGetCString(datum);
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
+			Assert(!isnull);
+			collctype = TextDatumGetCString(datum);
+
+			cache_entry->collate_is_c = ((strcmp(collcollate, "C") == 0) ||
+										 (strcmp(collcollate, "POSIX") == 0));
+			cache_entry->ctype_is_c = ((strcmp(collctype, "C") == 0) ||
+									   (strcmp(collctype, "POSIX") == 0));
+		}
+		else
+		{
+			cache_entry->collate_is_c = false;
+			cache_entry->ctype_is_c = false;
+		}
 
 		cache_entry->flags_valid = true;
 
@@ -1336,6 +1351,9 @@ lc_collate_is_c(Oid collation)
 		static int	result = -1;
 		char	   *localeptr;
 
+		if (default_locale.provider == COLLPROVIDER_ICU)
+			return false;
+
 		if (result >= 0)
 			return (bool) result;
 		localeptr = setlocale(LC_COLLATE, NULL);
@@ -1386,6 +1404,9 @@ lc_ctype_is_c(Oid collation)
 		static int	result = -1;
 		char	   *localeptr;
 
+		if (default_locale.provider == COLLPROVIDER_ICU)
+			return false;
+
 		if (result >= 0)
 			return (bool) result;
 		localeptr = setlocale(LC_CTYPE, NULL);
@@ -1414,6 +1435,88 @@ lc_ctype_is_c(Oid collation)
 	return (lookup_collation_cache(collation, true))->ctype_is_c;
 }
 
+struct pg_locale_struct default_locale;
+
+void
+make_icu_collator(const char *icucollstr,
+				  struct pg_locale_struct *resultp)
+{
+#ifdef USE_ICU
+	UCollator  *collator;
+	UErrorCode	status;
+
+	status = U_ZERO_ERROR;
+	collator = ucol_open(icucollstr, &status);
+	if (U_FAILURE(status))
+		ereport(ERROR,
+				(errmsg("could not open collator for locale \"%s\": %s",
+						icucollstr, u_errorName(status))));
+
+	if (U_ICU_VERSION_MAJOR_NUM < 54)
+		icu_set_collation_attributes(collator, icucollstr);
+
+	/* We will leak this string if we get an error below :-( */
+	resultp->info.icu.locale = MemoryContextStrdup(TopMemoryContext, icucollstr);
+	resultp->info.icu.ucol = collator;
+#else							/* not USE_ICU */
+	/* could get here if a collation was created by a build with ICU */
+	ereport(ERROR,
+			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+			 errmsg("ICU is not supported in this build"), \
+			 errhint("You need to rebuild PostgreSQL using %s.", "--with-icu")));
+#endif							/* not USE_ICU */
+}
+
+void
+check_collation_version(HeapTuple colltuple)
+{
+	Form_pg_collation collform;
+	Datum		collversion;
+	bool		isnull;
+
+	collform = (Form_pg_collation) GETSTRUCT(colltuple);
+
+	collversion = SysCacheGetAttr(COLLOID, colltuple, Anum_pg_collation_collversion,
+								  &isnull);
+	if (!isnull)
+	{
+		char	   *actual_versionstr;
+		char	   *collversionstr;
+		Datum		datum;
+		bool		isnull;
+
+		datum = SysCacheGetAttr(COLLOID, colltuple, collform->collprovider == COLLPROVIDER_ICU ? Anum_pg_collation_collicucoll : Anum_pg_collation_collcollate, &isnull);
+		Assert(!isnull);
+
+		actual_versionstr = get_collation_actual_version(collform->collprovider,
+														 TextDatumGetCString(datum));
+		if (!actual_versionstr)
+		{
+			/*
+			 * This could happen when specifying a version in CREATE
+			 * COLLATION for a libc locale, or manually creating a mess in
+			 * the catalogs.
+			 */
+			ereport(ERROR,
+					(errmsg("collation \"%s\" has no actual version, but a version was specified",
+							NameStr(collform->collname))));
+		}
+		collversionstr = TextDatumGetCString(collversion);
+
+		if (strcmp(actual_versionstr, collversionstr) != 0)
+			ereport(WARNING,
+					(errmsg("collation \"%s\" has version mismatch",
+							NameStr(collform->collname)),
+					 errdetail("The collation in the database was created using version %s, "
+							   "but the operating system provides version %s.",
+							   collversionstr, actual_versionstr),
+					 errhint("Rebuild all objects affected by this collation and run "
+							 "ALTER COLLATION %s REFRESH VERSION, "
+							 "or build PostgreSQL with the right library version.",
+							 quote_qualified_identifier(get_namespace_name(collform->collnamespace),
+														NameStr(collform->collname)))));
+	}
+}
 
 /* simple subroutine for reporting errors from newlocale() */
 #ifdef HAVE_LOCALE_T
@@ -1483,21 +1586,14 @@ pg_newlocale_from_collation(Oid collid)
 		/* We haven't computed this yet in this session, so do it */
 		HeapTuple	tp;
 		Form_pg_collation collform;
-		const char *collcollate;
-		const char *collctype pg_attribute_unused();
 		struct pg_locale_struct result;
 		pg_locale_t resultp;
-		Datum		collversion;
-		bool		isnull;
 
 		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(collid));
 		if (!HeapTupleIsValid(tp))
 			elog(ERROR, "cache lookup failed for collation %u", collid);
 		collform = (Form_pg_collation) GETSTRUCT(tp);
 
-		collcollate = NameStr(collform->collcollate);
-		collctype = NameStr(collform->collctype);
-
 		/* We'll fill in the result struct locally before allocating memory */
 		memset(&result, 0, sizeof(result));
 		result.provider = collform->collprovider;
@@ -1506,8 +1602,19 @@ pg_newlocale_from_collation(Oid collid)
 		if (collform->collprovider == COLLPROVIDER_LIBC)
 		{
 #ifdef HAVE_LOCALE_T
+			Datum		datum;
+			bool		isnull;
+			const char *collcollate;
+			const char *collctype pg_attribute_unused();
 			locale_t	loc;
 
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collcollate, &isnull);
+			Assert(!isnull);
+			collcollate = TextDatumGetCString(datum);
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collctype, &isnull);
+			Assert(!isnull);
+			collctype = TextDatumGetCString(datum);
+
 			if (strcmp(collcollate, collctype) == 0)
 			{
 				/* Normal case where they're the same */
@@ -1558,72 +1665,17 @@ pg_newlocale_from_collation(Oid collid)
 		}
 		else if (collform->collprovider == COLLPROVIDER_ICU)
 		{
-#ifdef USE_ICU
-			UCollator  *collator;
-			UErrorCode	status;
-
-			if (strcmp(collcollate, collctype) != 0)
-				ereport(ERROR,
-						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-						 errmsg("collations with different collate and ctype values are not supported by ICU")));
-
-			status = U_ZERO_ERROR;
-			collator = ucol_open(collcollate, &status);
-			if (U_FAILURE(status))
-				ereport(ERROR,
-						(errmsg("could not open collator for locale \"%s\": %s",
-								collcollate, u_errorName(status))));
-
-			if (U_ICU_VERSION_MAJOR_NUM < 54)
-				icu_set_collation_attributes(collator, collcollate);
-
-			/* We will leak this string if we get an error below :-( */
-			result.info.icu.locale = MemoryContextStrdup(TopMemoryContext,
-														 collcollate);
-			result.info.icu.ucol = collator;
-#else							/* not USE_ICU */
-			/* could get here if a collation was created by a build with ICU */
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("ICU is not supported in this build"), \
-					 errhint("You need to rebuild PostgreSQL using %s.", "--with-icu")));
-#endif							/* not USE_ICU */
+			Datum		datum;
+			bool		isnull;
+			const char *icucollstr;;
+
+			datum = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collicucoll, &isnull);
+			Assert(!isnull);
+			icucollstr = TextDatumGetCString(datum);
+			make_icu_collator(icucollstr, &result);
 		}
 
-		collversion = SysCacheGetAttr(COLLOID, tp, Anum_pg_collation_collversion,
-									  &isnull);
-		if (!isnull)
-		{
-			char	   *actual_versionstr;
-			char	   *collversionstr;
-
-			actual_versionstr = get_collation_actual_version(collform->collprovider, collcollate);
-			if (!actual_versionstr)
-			{
-				/*
-				 * This could happen when specifying a version in CREATE
-				 * COLLATION for a libc locale, or manually creating a mess in
-				 * the catalogs.
-				 */
-				ereport(ERROR,
-						(errmsg("collation \"%s\" has no actual version, but a version was specified",
-								NameStr(collform->collname))));
-			}
-			collversionstr = TextDatumGetCString(collversion);
-
-			if (strcmp(actual_versionstr, collversionstr) != 0)
-				ereport(WARNING,
-						(errmsg("collation \"%s\" has version mismatch",
-								NameStr(collform->collname)),
-						 errdetail("The collation in the database was created using version %s, "
-								   "but the operating system provides version %s.",
-								   collversionstr, actual_versionstr),
-						 errhint("Rebuild all objects affected by this collation and run "
-								 "ALTER COLLATION %s REFRESH VERSION, "
-								 "or build PostgreSQL with the right library version.",
-								 quote_qualified_identifier(get_namespace_name(collform->collnamespace),
-															NameStr(collform->collname)))));
-		}
+		check_collation_version(tp);
 
 		ReleaseSysCache(tp);
 
@@ -1646,6 +1698,17 @@ get_collation_actual_version(char collprovider, const char *collcollate)
 {
 	char	   *collversion = NULL;
 
+	if (collprovider == COLLPROVIDER_DEFAULT)
+	{
+#ifdef USE_ICU
+		if (default_locale.provider == COLLPROVIDER_ICU)
+			collversion = get_collation_actual_version(default_locale.provider,
+													   default_locale.info.icu.locale);
+		else
+#endif
+			collversion = NULL;
+	}
+	else
 #ifdef USE_ICU
 	if (collprovider == COLLPROVIDER_ICU)
 	{
diff --git a/src/backend/utils/adt/varchar.c b/src/backend/utils/adt/varchar.c
index 8fc84649f1..7eb9e59a2c 100644
--- a/src/backend/utils/adt/varchar.c
+++ b/src/backend/utils/adt/varchar.c
@@ -750,7 +750,7 @@ bpchareq(PG_FUNCTION_ARGS)
 	len2 = bcTruelen(arg2);
 
 	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
+		(collid == DEFAULT_COLLATION_OID && default_locale.deterministic) ||
 		pg_newlocale_from_collation(collid)->deterministic)
 	{
 		/*
@@ -790,7 +790,7 @@ bpcharne(PG_FUNCTION_ARGS)
 	len2 = bcTruelen(arg2);
 
 	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
+		(collid == DEFAULT_COLLATION_OID && default_locale.deterministic) ||
 		pg_newlocale_from_collation(collid)->deterministic)
 	{
 		/*
@@ -996,8 +996,13 @@ hashbpchar(PG_FUNCTION_ARGS)
 	keydata = VARDATA_ANY(key);
 	keylen = bcTruelen(key);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
+	}
 
 	if (!mylocale || mylocale->deterministic)
 	{
@@ -1056,8 +1061,13 @@ hashbpcharextended(PG_FUNCTION_ARGS)
 	keydata = VARDATA_ANY(key);
 	keylen = bcTruelen(key);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
+	}
 
 	if (!mylocale || mylocale->deterministic)
 	{
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index bd3091bbfb..5492c85f36 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -1200,8 +1200,13 @@ text_position_setup(text *t1, text *t2, Oid collid, TextPositionState *state)
 
 	check_collation_set(collid);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
+	}
 
 	if (mylocale && !mylocale->deterministic)
 		ereport(ERROR,
@@ -1560,6 +1565,8 @@ varstr_cmp(const char *arg1, int len1, const char *arg2, int len2, Oid collid)
 
 		if (collid != DEFAULT_COLLATION_OID)
 			mylocale = pg_newlocale_from_collation(collid);
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
 
 		/*
 		 * memcmp() can't tell us which of two unequal strings sorts first,
@@ -1781,7 +1788,7 @@ texteq(PG_FUNCTION_ARGS)
 	check_collation_set(collid);
 
 	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
+		(collid == DEFAULT_COLLATION_OID && default_locale.deterministic) ||
 		pg_newlocale_from_collation(collid)->deterministic)
 	{
 		Datum		arg1 = PG_GETARG_DATUM(0);
@@ -1835,7 +1842,7 @@ textne(PG_FUNCTION_ARGS)
 	check_collation_set(collid);
 
 	if (lc_collate_is_c(collid) ||
-		collid == DEFAULT_COLLATION_OID ||
+		(collid == DEFAULT_COLLATION_OID && default_locale.deterministic) ||
 		pg_newlocale_from_collation(collid)->deterministic)
 	{
 		Datum		arg1 = PG_GETARG_DATUM(0);
@@ -1947,8 +1954,13 @@ text_starts_with(PG_FUNCTION_ARGS)
 
 	check_collation_set(collid);
 
-	if (!lc_collate_is_c(collid) && collid != DEFAULT_COLLATION_OID)
-		mylocale = pg_newlocale_from_collation(collid);
+	if (!lc_collate_is_c(collid))
+	{
+		if (collid != DEFAULT_COLLATION_OID)
+			mylocale = pg_newlocale_from_collation(collid);
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			mylocale = &default_locale;
+	}
 
 	if (mylocale && !mylocale->deterministic)
 		ereport(ERROR,
@@ -2063,6 +2075,8 @@ varstr_sortsupport(SortSupport ssup, Oid typid, Oid collid)
 		 */
 		if (collid != DEFAULT_COLLATION_OID)
 			locale = pg_newlocale_from_collation(collid);
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+			locale = &default_locale;
 
 		/*
 		 * There is a further exception on Windows.  When the database
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 7292e51f7d..2319166e91 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -30,6 +30,7 @@
 #include "catalog/catalog.h"
 #include "catalog/namespace.h"
 #include "catalog/pg_authid.h"
+#include "catalog/pg_collation.h"
 #include "catalog/pg_database.h"
 #include "catalog/pg_db_role_setting.h"
 #include "catalog/pg_tablespace.h"
@@ -53,6 +54,7 @@
 #include "storage/sync.h"
 #include "tcop/tcopprot.h"
 #include "utils/acl.h"
+#include "utils/builtins.h"
 #include "utils/fmgroids.h"
 #include "utils/guc.h"
 #include "utils/memutils.h"
@@ -306,6 +308,8 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 {
 	HeapTuple	tup;
 	Form_pg_database dbform;
+	Datum		datum;
+	bool		isnull;
 	char	   *collate;
 	char	   *ctype;
 
@@ -389,8 +393,12 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 					PGC_BACKEND, PGC_S_DYNAMIC_DEFAULT);
 
 	/* assign locale variables */
-	collate = NameStr(dbform->datcollate);
-	ctype = NameStr(dbform->datctype);
+	datum = SysCacheGetAttr(DATABASEOID, tup, Anum_pg_database_datcollate, &isnull);
+	Assert(!isnull);
+	collate = TextDatumGetCString(datum);
+	datum = SysCacheGetAttr(DATABASEOID, tup, Anum_pg_database_datctype, &isnull);
+	Assert(!isnull);
+	ctype = TextDatumGetCString(datum);
 
 	if (pg_perm_setlocale(LC_COLLATE, collate) == NULL)
 		ereport(FATAL,
@@ -406,6 +414,31 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 						   " which is not recognized by setlocale().", ctype),
 				 errhint("Recreate the database with another locale or install the missing locale.")));
 
+	if (dbform->datcollprovider == COLLPROVIDER_ICU)
+	{
+		datum = SysCacheGetAttr(DATABASEOID, tup, Anum_pg_database_daticucoll, &isnull);
+		Assert(!isnull);
+		make_icu_collator(TextDatumGetCString(datum), &default_locale);
+	}
+
+	default_locale.provider = dbform->datcollprovider;
+	/*
+	 * Default locale is currently always deterministic.  Nondeterministic
+	 * locales currently don't support pattern matching, which would break a
+	 * lot of things if applied globally.
+	 */
+	default_locale.deterministic = true;
+
+	{
+		HeapTuple	tp;
+
+		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(DEFAULT_COLLATION_OID));
+		if (!HeapTupleIsValid(tp))
+			elog(ERROR, "cache lookup failed for collation %u", DEFAULT_COLLATION_OID);
+		check_collation_version(tp);
+		ReleaseSysCache(tp);
+	}
+
 	/* Make the locale settings visible as GUC variables, too */
 	SetConfigOption("lc_collate", collate, PGC_INTERNAL, PGC_S_OVERRIDE);
 	SetConfigOption("lc_ctype", ctype, PGC_INTERNAL, PGC_S_OVERRIDE);
diff --git a/src/bin/initdb/Makefile b/src/bin/initdb/Makefile
index a620a5bea0..993d2fa7a3 100644
--- a/src/bin/initdb/Makefile
+++ b/src/bin/initdb/Makefile
@@ -62,6 +62,8 @@ clean distclean maintainer-clean:
 # ensure that changes in datadir propagate into object file
 initdb.o: initdb.c $(top_builddir)/src/Makefile.global
 
+export with_icu
+
 check:
 	$(prove_check)
 
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index 03b80f9575..9ee0037d50 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -131,6 +131,8 @@ static char *lc_monetary = NULL;
 static char *lc_numeric = NULL;
 static char *lc_time = NULL;
 static char *lc_messages = NULL;
+static char collation_provider[] = {COLLPROVIDER_LIBC, '\0'};
+static char *icu_locale = NULL;
 static const char *default_text_search_config = NULL;
 static char *username = NULL;
 static bool pwprompt = false;
@@ -1404,6 +1406,12 @@ bootstrap_template1(void)
 	bki_lines = replace_token(bki_lines, "LC_CTYPE",
 							  escape_quotes_bki(lc_ctype));
 
+	bki_lines = replace_token(bki_lines, "ICUCOLL",
+							  escape_quotes_bki(collation_provider[0] == COLLPROVIDER_ICU ? icu_locale : "_null_"));
+
+	bki_lines = replace_token(bki_lines, "COLLPROVIDER",
+							  collation_provider);
+
 	/* Also ensure backend isn't confused by this environment var: */
 	unsetenv("PGCLIENTENCODING");
 
@@ -1586,6 +1594,12 @@ setup_description(FILE *cmdfd)
 static void
 setup_collation(FILE *cmdfd)
 {
+	/*
+	 * Set version of the default collation.
+	 */
+	PG_CMD_PRINTF("UPDATE pg_collation SET collversion = pg_collation_actual_version(oid) WHERE oid = %d;\n\n",
+				  DEFAULT_COLLATION_OID);
+
 	/*
 	 * Add an SQL-standard name.  We don't want to pin this, so it doesn't go
 	 * in pg_collation.h.  But add it before reading system collations, so
@@ -1839,8 +1853,6 @@ make_template0(FILE *cmdfd)
 {
 	const char *const *line;
 	static const char *const template0_setup[] = {
-		"CREATE DATABASE template0 IS_TEMPLATE = true ALLOW_CONNECTIONS = false;\n\n",
-
 		/*
 		 * We use the OID of template0 to determine datlastsysoid
 		 */
@@ -1865,6 +1877,9 @@ make_template0(FILE *cmdfd)
 		NULL
 	};
 
+	PG_CMD_PRINTF("CREATE DATABASE template0 IS_TEMPLATE = true ALLOW_CONNECTIONS = false COLLATION_PROVIDER = %s;\n\n",
+				  collation_provider[0] == COLLPROVIDER_ICU ? "icu" : "libc");
+
 	for (line = template0_setup; *line; line++)
 		PG_CMD_PUTS(*line);
 }
@@ -2136,13 +2151,14 @@ setlocales(void)
 			lc_monetary = locale;
 		if (!lc_messages)
 			lc_messages = locale;
+		if (!icu_locale)
+			icu_locale = locale;
 	}
 
 	/*
 	 * canonicalize locale names, and obtain any missing values from our
 	 * current environment
 	 */
-
 	check_locale_name(LC_CTYPE, lc_ctype, &canonname);
 	lc_ctype = canonname;
 	check_locale_name(LC_COLLATE, lc_collate, &canonname);
@@ -2161,6 +2177,18 @@ setlocales(void)
 	check_locale_name(LC_CTYPE, lc_messages, &canonname);
 	lc_messages = canonname;
 #endif
+
+	/*
+	 * If ICU is selected but no ICU locale has been given, take the
+	 * lc_collate locale and chop off any encoding suffix.  This should give
+	 * the user a configuration that resembles their operating system's locale
+	 * setup.
+	 */
+	if (collation_provider[0] == COLLPROVIDER_ICU && !icu_locale)
+	{
+		icu_locale = pg_strdup(lc_collate);
+		icu_locale[strcspn(icu_locale, ".")] = '\0';
+	}
 }
 
 /*
@@ -2176,9 +2204,12 @@ usage(const char *progname)
 	printf(_("  -A, --auth=METHOD         default authentication method for local connections\n"));
 	printf(_("      --auth-host=METHOD    default authentication method for local TCP/IP connections\n"));
 	printf(_("      --auth-local=METHOD   default authentication method for local-socket connections\n"));
+	printf(_("      --collation-provider={libc|icu}\n"
+			 "                            set default collation provider for new databases\n"));
 	printf(_(" [-D, --pgdata=]DATADIR     location for this database cluster\n"));
 	printf(_("  -E, --encoding=ENCODING   set default encoding for new databases\n"));
 	printf(_("  -g, --allow-group-access  allow group read/execute on data directory\n"));
+	printf(_("      --icu-locale          set ICU locale for new databases\n"));
 	printf(_("  -k, --data-checksums      use data page checksums\n"));
 	printf(_("      --locale=LOCALE       set default locale for new databases\n"));
 	printf(_("      --lc-collate=, --lc-ctype=, --lc-messages=LOCALE\n"
@@ -2353,7 +2384,8 @@ setup_locale_encoding(void)
 		strcmp(lc_ctype, lc_time) == 0 &&
 		strcmp(lc_ctype, lc_numeric) == 0 &&
 		strcmp(lc_ctype, lc_monetary) == 0 &&
-		strcmp(lc_ctype, lc_messages) == 0)
+		strcmp(lc_ctype, lc_messages) == 0 &&
+		(!icu_locale || strcmp(lc_ctype, icu_locale) == 0))
 		printf(_("The database cluster will be initialized with locale \"%s\".\n"), lc_ctype);
 	else
 	{
@@ -2370,9 +2402,13 @@ setup_locale_encoding(void)
 			   lc_monetary,
 			   lc_numeric,
 			   lc_time);
+		if (icu_locale)
+			printf(_("  ICU:      %s\n"), icu_locale);
 	}
 
-	if (!encoding)
+	if (!encoding && collation_provider[0] == COLLPROVIDER_ICU)
+		encodingid = PG_UTF8;
+	else if (!encoding)
 	{
 		int			ctype_enc;
 
@@ -2876,6 +2912,8 @@ main(int argc, char *argv[])
 		{"data-checksums", no_argument, NULL, 'k'},
 		{"allow-group-access", no_argument, NULL, 'g'},
 		{"discard-caches", no_argument, NULL, 14},
+		{"collation-provider", required_argument, NULL, 15},
+		{"icu-locale", required_argument, NULL, 16},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -3022,6 +3060,20 @@ main(int argc, char *argv[])
 										 extra_options,
 										 "-c debug_discard_caches=1");
 				break;
+			case 15:
+				if (strcmp(optarg, "icu") == 0)
+					collation_provider[0] = COLLPROVIDER_ICU;
+				else if (strcmp(optarg, "libc") == 0)
+					collation_provider[0] = COLLPROVIDER_LIBC;
+				else
+				{
+					pg_log_error("unrecognized collation provider: %s", optarg);
+					exit(1);
+				}
+				break;
+			case 16:
+				icu_locale = pg_strdup(optarg);
+				break;
 			default:
 				/* getopt_long already emitted a complaint */
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
diff --git a/src/bin/initdb/t/001_initdb.pl b/src/bin/initdb/t/001_initdb.pl
index 6796d8520e..6b3208a03d 100644
--- a/src/bin/initdb/t/001_initdb.pl
+++ b/src/bin/initdb/t/001_initdb.pl
@@ -11,7 +11,7 @@
 use File::stat qw{lstat};
 use PostgreSQL::Test::Cluster;
 use PostgreSQL::Test::Utils;
-use Test::More tests => 22;
+use Test::More tests => 24;
 
 my $tempdir = PostgreSQL::Test::Utils::tempdir;
 my $xlogdir = "$tempdir/pgxlog";
@@ -92,3 +92,19 @@
 	ok(check_mode_recursive($datadir_group, 0750, 0640),
 		'check PGDATA permissions');
 }
+
+# Collation provider tests
+
+if ($ENV{with_icu} eq 'yes')
+{
+	command_ok(['initdb', '--no-sync', '--collation-provider=icu', "$tempdir/data2"],
+			   'collation provider ICU');
+}
+else
+{
+	command_fails(['initdb', '--no-sync', '--collation-provider=icu', "$tempdir/data2"],
+				  'collation provider ICU fails since no ICU support');
+}
+
+command_fails(['initdb', '--no-sync', '--collation-provider=xyz', "$tempdir/dataX"],
+			  'fails for invalid collation provider');
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index b52f3ccda2..7c6af8d2ef 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -2740,6 +2740,7 @@ dumpDatabase(Archive *fout)
 				i_datname,
 				i_dba,
 				i_encoding,
+				i_datcollprovider,
 				i_collate,
 				i_ctype,
 				i_frozenxid,
@@ -2755,6 +2756,7 @@ dumpDatabase(Archive *fout)
 	const char *datname,
 			   *dba,
 			   *encoding,
+			   *datcollprovider,
 			   *collate,
 			   *ctype,
 			   *datistemplate,
@@ -2774,6 +2776,7 @@ dumpDatabase(Archive *fout)
 		appendPQExpBuffer(dbQry, "SELECT tableoid, oid, datname, "
 						  "(%s datdba) AS dba, "
 						  "pg_encoding_to_char(encoding) AS encoding, "
+						  "datcollprovider, "
 						  "datcollate, datctype, datfrozenxid, datminmxid, "
 						  "datacl, acldefault('d', datdba) AS acldefault, "
 						  "datistemplate, datconnlimit, "
@@ -2807,6 +2810,7 @@ dumpDatabase(Archive *fout)
 	i_datname = PQfnumber(res, "datname");
 	i_dba = PQfnumber(res, "dba");
 	i_encoding = PQfnumber(res, "encoding");
+	i_datcollprovider = PQfnumber(res, "datcollprovider");
 	i_collate = PQfnumber(res, "datcollate");
 	i_ctype = PQfnumber(res, "datctype");
 	i_frozenxid = PQfnumber(res, "datfrozenxid");
@@ -2822,6 +2826,7 @@ dumpDatabase(Archive *fout)
 	datname = PQgetvalue(res, 0, i_datname);
 	dba = PQgetvalue(res, 0, i_dba);
 	encoding = PQgetvalue(res, 0, i_encoding);
+	datcollprovider = PQgetvalue(res, 0, i_datcollprovider);
 	collate = PQgetvalue(res, 0, i_collate);
 	ctype = PQgetvalue(res, 0, i_ctype);
 	frozenxid = atooid(PQgetvalue(res, 0, i_frozenxid));
@@ -2847,6 +2852,17 @@ dumpDatabase(Archive *fout)
 		appendPQExpBufferStr(creaQry, " ENCODING = ");
 		appendStringLiteralAH(creaQry, encoding, fout);
 	}
+	if (strlen(datcollprovider) > 0)
+	{
+		appendPQExpBufferStr(creaQry, " COLLATION_PROVIDER = ");
+		if (datcollprovider[0] == 'c')
+			appendPQExpBufferStr(creaQry, "libc");
+		else if (datcollprovider[0] == 'i')
+			appendPQExpBufferStr(creaQry, "icu");
+		else
+			fatal("unrecognized collation provider: %s",
+				  datcollprovider);
+	}
 	if (strlen(collate) > 0 && strcmp(collate, ctype) == 0)
 	{
 		appendPQExpBufferStr(creaQry, " LOCALE = ");
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index c28788e84f..0d710bd47e 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -896,6 +896,18 @@ listAllDbs(const char *pattern, bool verbose)
 					  gettext_noop("Encoding"),
 					  gettext_noop("Collate"),
 					  gettext_noop("Ctype"));
+	if (pset.sversion >= 150000)
+		appendPQExpBuffer(&buf,
+						  "       d.daticucoll as \"%s\",\n"
+						  "       CASE d.datcollprovider WHEN 'c' THEN 'libc' WHEN 'i' THEN 'icu' END AS \"%s\",\n",
+						  gettext_noop("ICU Collation"),
+						  gettext_noop("Coll. Provider"));
+	else
+		appendPQExpBuffer(&buf,
+						  "       d.datcollate as \"%s\",\n"
+						  "       'libc' AS \"%s\",\n",
+						  gettext_noop("ICU Collation"),
+						  gettext_noop("Coll. Provider"));
 	appendPQExpBufferStr(&buf, "       ");
 	printACLColumn(&buf, "d.datacl");
 	if (verbose)
@@ -4573,7 +4585,7 @@ listCollations(const char *pattern, bool verbose, bool showSystem)
 	PQExpBufferData buf;
 	PGresult   *res;
 	printQueryOpt myopt = pset.popt;
-	static const bool translate_columns[] = {false, false, false, false, false, true, false};
+	static const bool translate_columns[] = {false, false, false, false, false, false, true, false};
 
 	initPQExpBuffer(&buf);
 
@@ -4587,6 +4599,15 @@ listCollations(const char *pattern, bool verbose, bool showSystem)
 					  gettext_noop("Collate"),
 					  gettext_noop("Ctype"));
 
+	if (pset.sversion >= 150000)
+		appendPQExpBuffer(&buf,
+						  ",\n       c.collicucoll AS \"%s\"",
+						  gettext_noop("ICU Collation"));
+	else
+		appendPQExpBuffer(&buf,
+						  ",\n       c.collcollate AS \"%s\"",
+						  gettext_noop("ICU Collation"));
+
 	if (pset.sversion >= 100000)
 		appendPQExpBuffer(&buf,
 						  ",\n       CASE c.collprovider WHEN 'd' THEN 'default' WHEN 'c' THEN 'libc' WHEN 'i' THEN 'icu' END AS \"%s\"",
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index cf30239f6d..7db4a68df6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -2587,7 +2587,7 @@ psql_completion(const char *text, int start, int end)
 		COMPLETE_WITH("OWNER", "TEMPLATE", "ENCODING", "TABLESPACE",
 					  "IS_TEMPLATE",
 					  "ALLOW_CONNECTIONS", "CONNECTION LIMIT",
-					  "LC_COLLATE", "LC_CTYPE", "LOCALE");
+					  "LC_COLLATE", "LC_CTYPE", "LOCALE", "COLLATION_PROVIDER");
 
 	else if (Matches("CREATE", "DATABASE", MatchAny, "TEMPLATE"))
 		COMPLETE_WITH_QUERY(Query_for_list_of_template_databases);
diff --git a/src/bin/scripts/Makefile b/src/bin/scripts/Makefile
index b8d7cf2f2d..342a57d71b 100644
--- a/src/bin/scripts/Makefile
+++ b/src/bin/scripts/Makefile
@@ -53,6 +53,8 @@ clean distclean maintainer-clean:
 	rm -f common.o $(WIN32RES)
 	rm -rf tmp_check
 
+export with_icu
+
 check:
 	$(prove_check)
 
diff --git a/src/bin/scripts/createdb.c b/src/bin/scripts/createdb.c
index 041454f075..1944580f36 100644
--- a/src/bin/scripts/createdb.c
+++ b/src/bin/scripts/createdb.c
@@ -38,6 +38,7 @@ main(int argc, char *argv[])
 		{"lc-ctype", required_argument, NULL, 2},
 		{"locale", required_argument, NULL, 'l'},
 		{"maintenance-db", required_argument, NULL, 3},
+		{"collation-provider", required_argument, NULL, 4},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -61,6 +62,7 @@ main(int argc, char *argv[])
 	char	   *lc_collate = NULL;
 	char	   *lc_ctype = NULL;
 	char	   *locale = NULL;
+	char	   *collation_provider = NULL;
 
 	PQExpBufferData sql;
 
@@ -119,6 +121,9 @@ main(int argc, char *argv[])
 			case 3:
 				maintenance_db = pg_strdup(optarg);
 				break;
+			case 4:
+				collation_provider = pg_strdup(optarg);
+				break;
 			default:
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
 				exit(1);
@@ -217,6 +222,8 @@ main(int argc, char *argv[])
 		appendPQExpBufferStr(&sql, " LC_CTYPE ");
 		appendStringLiteralConn(&sql, lc_ctype, conn);
 	}
+	if (collation_provider)
+		appendPQExpBuffer(&sql, " COLLATION_PROVIDER %s", collation_provider);
 
 	appendPQExpBufferChar(&sql, ';');
 
@@ -267,6 +274,8 @@ help(const char *progname)
 	printf(_("Usage:\n"));
 	printf(_("  %s [OPTION]... [DBNAME] [DESCRIPTION]\n"), progname);
 	printf(_("\nOptions:\n"));
+	printf(_("      --collation-provider={libc|icu}\n"
+			 "                               collation provider for the database's default collation\n"));
 	printf(_("  -D, --tablespace=TABLESPACE  default tablespace for the database\n"));
 	printf(_("  -e, --echo                   show the commands being sent to the server\n"));
 	printf(_("  -E, --encoding=ENCODING      encoding for the database\n"));
diff --git a/src/bin/scripts/t/020_createdb.pl b/src/bin/scripts/t/020_createdb.pl
index 6bcc59de08..e1a4af384c 100644
--- a/src/bin/scripts/t/020_createdb.pl
+++ b/src/bin/scripts/t/020_createdb.pl
@@ -6,7 +6,7 @@
 
 use PostgreSQL::Test::Cluster;
 use PostgreSQL::Test::Utils;
-use Test::More tests => 25;
+use Test::More tests => 28;
 
 program_help_ok('createdb');
 program_version_ok('createdb');
@@ -25,9 +25,27 @@
 	qr/statement: CREATE DATABASE foobar2 ENCODING 'LATIN1'/,
 	'create database with encoding');
 
+if ($ENV{with_icu} eq 'yes')
+{
+	$node->issues_sql_like(
+		[ 'createdb', '-T', 'template0', '--collation-provider=icu', 'foobar4' ],
+		qr/statement: CREATE DATABASE foobar4 .* COLLATION_PROVIDER icu/,
+		'create database with ICU');
+}
+else
+{
+	$node->command_fails(
+		[ 'createdb', '-T', 'template0', '--collation-provider=icu', 'foobar4' ],
+		'create database with ICU fails since no ICU support');
+	pass;
+}
+
 $node->command_fails([ 'createdb', 'foobar1' ],
 	'fails if database already exists');
 
+$node->command_fails([ 'createdb', '-T', 'template0', '--collation-provider=xyz', 'foobarX' ],
+	'fails for invalid collation provider');
+
 # Check use of templates with shared dependencies copied from the template.
 my ($ret, $stdout, $stderr) = $node->psql(
 	'foobar2',
diff --git a/src/include/catalog/pg_collation.dat b/src/include/catalog/pg_collation.dat
index 6e0ab1ab4b..2a8cf2be7c 100644
--- a/src/include/catalog/pg_collation.dat
+++ b/src/include/catalog/pg_collation.dat
@@ -14,8 +14,7 @@
 
 { oid => '100', oid_symbol => 'DEFAULT_COLLATION_OID',
   descr => 'database\'s default collation',
-  collname => 'default', collprovider => 'd', collencoding => '-1',
-  collcollate => '', collctype => '' },
+  collname => 'default', collprovider => 'd', collencoding => '-1' },
 { oid => '950', oid_symbol => 'C_COLLATION_OID',
   descr => 'standard C collation',
   collname => 'C', collprovider => 'c', collencoding => '-1',
diff --git a/src/include/catalog/pg_collation.h b/src/include/catalog/pg_collation.h
index 03bd4cb5d4..bff59abe92 100644
--- a/src/include/catalog/pg_collation.h
+++ b/src/include/catalog/pg_collation.h
@@ -39,9 +39,10 @@ CATALOG(pg_collation,3456,CollationRelationId)
 	char		collprovider;	/* see constants below */
 	bool		collisdeterministic BKI_DEFAULT(t);
 	int32		collencoding;	/* encoding for this collation; -1 = "all" */
-	NameData	collcollate;	/* LC_COLLATE setting */
-	NameData	collctype;		/* LC_CTYPE setting */
 #ifdef CATALOG_VARLEN			/* variable-length fields start here */
+	text		collcollate BKI_DEFAULT(_null_);	/* LC_COLLATE setting */
+	text		collctype BKI_DEFAULT(_null_);		/* LC_CTYPE setting */
+	text		collicucoll BKI_DEFAULT(_null_);	/* ICU collation string */
 	text		collversion BKI_DEFAULT(_null_);	/* provider-dependent
 													 * version of collation
 													 * data */
@@ -75,6 +76,7 @@ extern Oid	CollationCreate(const char *collname, Oid collnamespace,
 							bool collisdeterministic,
 							int32 collencoding,
 							const char *collcollate, const char *collctype,
+							const char *collicucoll,
 							const char *collversion,
 							bool if_not_exists,
 							bool quiet);
diff --git a/src/include/catalog/pg_database.dat b/src/include/catalog/pg_database.dat
index b8aa1364a0..6c62efcc54 100644
--- a/src/include/catalog/pg_database.dat
+++ b/src/include/catalog/pg_database.dat
@@ -15,7 +15,7 @@
 { oid => '1', oid_symbol => 'TemplateDbOid',
   descr => 'default template for new databases',
   datname => 'template1', encoding => 'ENCODING', datcollate => 'LC_COLLATE',
-  datctype => 'LC_CTYPE', datistemplate => 't', datallowconn => 't',
+  datctype => 'LC_CTYPE', daticucoll => 'ICUCOLL', datcollprovider => 'COLLPROVIDER', datistemplate => 't', datallowconn => 't',
   datconnlimit => '-1', datlastsysoid => '0', datfrozenxid => '0',
   datminmxid => '1', dattablespace => 'pg_default', datacl => '_null_' },
 
diff --git a/src/include/catalog/pg_database.h b/src/include/catalog/pg_database.h
index 43f3beb6a3..9280850185 100644
--- a/src/include/catalog/pg_database.h
+++ b/src/include/catalog/pg_database.h
@@ -40,11 +40,8 @@ CATALOG(pg_database,1262,DatabaseRelationId) BKI_SHARED_RELATION BKI_ROWTYPE_OID
 	/* character encoding */
 	int32		encoding;
 
-	/* LC_COLLATE setting */
-	NameData	datcollate;
-
-	/* LC_CTYPE setting */
-	NameData	datctype;
+	/* see pg_collation.collprovider */
+	char		datcollprovider;
 
 	/* allowed as CREATE DATABASE template? */
 	bool		datistemplate;
@@ -68,6 +65,15 @@ CATALOG(pg_database,1262,DatabaseRelationId) BKI_SHARED_RELATION BKI_ROWTYPE_OID
 	Oid			dattablespace BKI_LOOKUP(pg_tablespace);
 
 #ifdef CATALOG_VARLEN			/* variable-length fields start here */
+	/* LC_COLLATE setting */
+	text		datcollate BKI_FORCE_NOT_NULL;
+
+	/* LC_CTYPE setting */
+	text		datctype BKI_FORCE_NOT_NULL;
+
+	/* ICU collation */
+	text		daticucoll;
+
 	/* access permissions */
 	aclitem		datacl[1];
 #endif
diff --git a/src/include/utils/pg_locale.h b/src/include/utils/pg_locale.h
index 2946f46c76..19478e573f 100644
--- a/src/include/utils/pg_locale.h
+++ b/src/include/utils/pg_locale.h
@@ -101,6 +101,12 @@ struct pg_locale_struct
 
 typedef struct pg_locale_struct *pg_locale_t;
 
+extern struct pg_locale_struct default_locale;
+
+extern void make_icu_collator(const char *icucollstr,
+							  struct pg_locale_struct *resultp);
+extern void check_collation_version(HeapTuple colltuple);
+
 extern pg_locale_t pg_newlocale_from_collation(Oid collid);
 
 extern char *get_collation_actual_version(char collprovider, const char *collcollate);
diff --git a/src/test/regress/expected/collate.icu.utf8.out b/src/test/regress/expected/collate.icu.utf8.out
index 70133df804..3d9647b597 100644
--- a/src/test/regress/expected/collate.icu.utf8.out
+++ b/src/test/regress/expected/collate.icu.utf8.out
@@ -1029,14 +1029,12 @@ CREATE COLLATION test0 FROM "C"; -- fail, duplicate name
 ERROR:  collation "test0" already exists
 do $$
 BEGIN
-  EXECUTE 'CREATE COLLATION test1 (provider = icu, lc_collate = ' ||
-          quote_literal(current_setting('lc_collate')) ||
-          ', lc_ctype = ' ||
-          quote_literal(current_setting('lc_ctype')) || ');';
+  EXECUTE 'CREATE COLLATION test1 (provider = icu, locale = ' ||
+          quote_literal(current_setting('lc_collate')) || ');';
 END
 $$;
-CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, need lc_ctype
-ERROR:  parameter "lc_ctype" must be specified
+CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, needs "locale"
+ERROR:  parameter "locale" must be specified
 CREATE COLLATION testx (provider = icu, locale = 'nonsense'); /* never fails with ICU */  DROP COLLATION testx;
 CREATE COLLATION test4 FROM nonsense;
 ERROR:  collation "nonsense" for encoding "UTF8" does not exist
diff --git a/src/test/regress/sql/collate.icu.utf8.sql b/src/test/regress/sql/collate.icu.utf8.sql
index 9cee3d0042..0677ba56e4 100644
--- a/src/test/regress/sql/collate.icu.utf8.sql
+++ b/src/test/regress/sql/collate.icu.utf8.sql
@@ -366,13 +366,11 @@ CREATE SCHEMA test_schema;
 CREATE COLLATION test0 FROM "C"; -- fail, duplicate name
 do $$
 BEGIN
-  EXECUTE 'CREATE COLLATION test1 (provider = icu, lc_collate = ' ||
-          quote_literal(current_setting('lc_collate')) ||
-          ', lc_ctype = ' ||
-          quote_literal(current_setting('lc_ctype')) || ');';
+  EXECUTE 'CREATE COLLATION test1 (provider = icu, locale = ' ||
+          quote_literal(current_setting('lc_collate')) || ');';
 END
 $$;
-CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, need lc_ctype
+CREATE COLLATION test3 (provider = icu, lc_collate = 'en_US.utf8'); -- fail, needs "locale"
 CREATE COLLATION testx (provider = icu, locale = 'nonsense'); /* never fails with ICU */  DROP COLLATION testx;
 
 CREATE COLLATION test4 FROM nonsense;

base-commit: 8112bcf0cc602e00e95eab6c4bdc0eb73b5b547d
-- 
2.34.1