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From: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
To: pgsql-hackers <pgsql-hackers@postgresql.org>
Cc: Daniel Verite <daniel@manitou-mail.org>
Subject: Re: ICU for global collation
Date: Thu, 30 Dec 2021 13:07:21 +0100
Message-ID: <525ef44f-52bf-505f-a491-07835d039424@enterprisedb.com> (raw)
In-Reply-To: <d7060bf1-177c-e0f2-f13f-b857cdd1182e@2ndquadrant.com>
References: <374f8048-9d87-462c-a8aa-d02ffca6525f@manitou-mail.org>
	<d7060bf1-177c-e0f2-f13f-b857cdd1182e@2ndquadrant.com>


There were a few inquiries about this topic recently, so I dug up the 
old thread and patch.  What we got stuck on last time was that we can't 
just swap out all locale support in a database for ICU.  We still need 
to set the usual locale environment, otherwise some things that are not 
ICU aware will break or degrade.  I had initially anticipated fixing 
that by converting everything that uses libc locales to ICU.  But that 
turned out to be tedious and ultimately not very useful as far as the 
user-facing result is concerned, so I gave up.

So this is a different approach: If you choose ICU as the default locale 
for a database, you still need to specify lc_ctype and lc_collate 
settings, as before.  Unlike in the previous patch, where the ICU 
collation name was written in datcollate, there is now a third column 
(daticucoll), so we can store all three values.  This fixes the 
described problem.  Other than that, once you get all the initial 
settings right, it basically just works: The places that have ICU 
support now will use a database-wide ICU collation if appropriate, the 
places that don't have ICU support continue to use the global libc 
locale settings.

I changed the datcollate, datctype, and the new daticucoll fields to 
type text (from name).  That way, the daticucoll field can be set to 
null if it's not applicable.  Also, the limit of 63 characters can 
actually be a problem if you want to use some combination of the options 
that ICU locales offer.  And for less extreme uses, having 
variable-length fields will save some storage, since typical locale 
names are much shorter.

For the same reasons and to keep things consistent, I also changed the 
analogous pg_collation fields like that.  This also removes some weird 
code that has to check that colcollate and colctype have to be the same 
for ICU, so it's overall cleaner.
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



Attachments:

  [text/plain] v3-0001-Add-option-to-use-ICU-as-global-collation-provide.patch (69.7K, ../525ef44f-52bf-505f-a491-07835d039424@enterprisedb.com/2-v3-0001-Add-option-to-use-ICU-as-global-collation-provide.patch)
  download | inline diff:
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

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  To: pgsql-hackers@postgresql.org
  Cc: peter.eisentraut@enterprisedb.com, daniel@manitou-mail.org
  Subject: Re: ICU for global collation
  In-Reply-To: <525ef44f-52bf-505f-a491-07835d039424@enterprisedb.com>

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