Create an explicit concept of collations that work for any encoding.

Use collencoding = -1 to represent such a collation in pg_collation.
We need this to make the "default" entry work sanely, and a later
patch will fix the C/POSIX entries to be represented this way instead
of duplicating them across all encodings.  All lookup operations now
search first for an entry that's database-encoding-specific, and then
for the same name with collencoding = -1.

Also some incidental code cleanup in collationcmds.c and pg_collation.c.

src/backend/catalog/information_schema.sql

@@ -448,7 +448,7 @@ CREATE VIEW collations AS
            CAST('NO PAD' AS character_data) AS pad_attribute
     FROM pg_collation c, pg_namespace nc
     WHERE c.collnamespace = nc.oid
-          AND collencoding = (SELECT encoding FROM pg_catalog.pg_database WHERE datname = pg_catalog.current_database());
+          AND collencoding IN (-1, (SELECT encoding FROM pg_database WHERE datname = current_database()));
 
 GRANT SELECT ON collations TO PUBLIC;
 
@@ -467,7 +467,7 @@ CREATE VIEW collation_character_set_applicability AS
            CAST(getdatabaseencoding() AS sql_identifier) AS character_set_name
     FROM pg_collation c, pg_namespace nc
     WHERE c.collnamespace = nc.oid
-          AND collencoding = (SELECT encoding FROM pg_catalog.pg_database WHERE datname = pg_catalog.current_database());
+          AND collencoding IN (-1, (SELECT encoding FROM pg_database WHERE datname = current_database()));
 
 GRANT SELECT ON collation_character_set_applicability TO PUBLIC;
 
@@ -2036,7 +2036,7 @@ CREATE VIEW usage_privileges AS
 
     WHERE u.oid = c.collowner
           AND c.collnamespace = n.oid
-          AND c.collencoding = (SELECT encoding FROM pg_catalog.pg_database WHERE datname = pg_catalog.current_database())
+          AND collencoding IN (-1, (SELECT encoding FROM pg_database WHERE datname = current_database()))
 
     UNION ALL
 

src/backend/catalog/namespace.c

@@ -1617,13 +1617,11 @@ OpfamilyIsVisible(Oid opfid)
  * CollationGetCollid
  *		Try to resolve an unqualified collation name.
  *		Returns OID if collation found in search path, else InvalidOid.
- *
- * This is essentially the same as RelnameGetRelid.
  */
 Oid
 CollationGetCollid(const char *collname)
 {
-	Oid			collid;
+	int32		dbencoding = GetDatabaseEncoding();
 	ListCell   *l;
 
 	recomputeNamespacePath();
@@ -1631,13 +1629,23 @@ CollationGetCollid(const char *collname)
 	foreach(l, activeSearchPath)
 	{
 		Oid			namespaceId = lfirst_oid(l);
+		Oid			collid;
 
 		if (namespaceId == myTempNamespace)
 			continue;			/* do not look in temp namespace */
 
+		/* Check for database-encoding-specific entry */
 		collid = GetSysCacheOid3(COLLNAMEENCNSP,
 								 PointerGetDatum(collname),
-								 Int32GetDatum(GetDatabaseEncoding()),
+								 Int32GetDatum(dbencoding),
+								 ObjectIdGetDatum(namespaceId));
+		if (OidIsValid(collid))
+			return collid;
+
+		/* Check for any-encoding entry */
+		collid = GetSysCacheOid3(COLLNAMEENCNSP,
+								 PointerGetDatum(collname),
+								 Int32GetDatum(-1),
 								 ObjectIdGetDatum(namespaceId));
 		if (OidIsValid(collid))
 			return collid;
@@ -2901,12 +2909,10 @@ get_collation_oid(List *name, bool missing_ok)
 {
 	char	   *schemaname;
 	char	   *collation_name;
+	int32		dbencoding = GetDatabaseEncoding();
 	Oid			namespaceId;
-	Oid			colloid = InvalidOid;
+	Oid			colloid;
 	ListCell   *l;
-	int			encoding;
-
-	encoding = GetDatabaseEncoding();
 
 	/* deconstruct the name list */
 	DeconstructQualifiedName(name, &schemaname, &collation_name);
@@ -2915,10 +2921,20 @@ get_collation_oid(List *name, bool missing_ok)
 	{
 		/* use exact schema given */
 		namespaceId = LookupExplicitNamespace(schemaname);
+
+		/* first try for encoding-specific entry, then any-encoding */
 		colloid = GetSysCacheOid3(COLLNAMEENCNSP,
 								  PointerGetDatum(collation_name),
-								  Int32GetDatum(encoding),
+								  Int32GetDatum(dbencoding),
 								  ObjectIdGetDatum(namespaceId));
+		if (OidIsValid(colloid))
+			return colloid;
+		colloid = GetSysCacheOid3(COLLNAMEENCNSP,
+								  PointerGetDatum(collation_name),
+								  Int32GetDatum(-1),
+								  ObjectIdGetDatum(namespaceId));
+		if (OidIsValid(colloid))
+			return colloid;
 	}
 	else
 	{
@@ -2934,7 +2950,13 @@ get_collation_oid(List *name, bool missing_ok)
 
 			colloid = GetSysCacheOid3(COLLNAMEENCNSP,
 									  PointerGetDatum(collation_name),
-									  Int32GetDatum(encoding),
+									  Int32GetDatum(dbencoding),
+									  ObjectIdGetDatum(namespaceId));
+			if (OidIsValid(colloid))
+				return colloid;
+			colloid = GetSysCacheOid3(COLLNAMEENCNSP,
+									  PointerGetDatum(collation_name),
+									  Int32GetDatum(-1),
 									  ObjectIdGetDatum(namespaceId));
 			if (OidIsValid(colloid))
 				return colloid;
@@ -2942,12 +2964,12 @@ get_collation_oid(List *name, bool missing_ok)
 	}
 
 	/* Not found in path */
-	if (!OidIsValid(colloid) && !missing_ok)
+	if (!missing_ok)
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_OBJECT),
-				 errmsg("collation \"%s\" for current database encoding \"%s\" does not exist",
+				 errmsg("collation \"%s\" for encoding \"%s\" does not exist",
 						NameListToString(name), GetDatabaseEncodingName())));
-	return colloid;
+	return InvalidOid;
 }
 
 /*

src/backend/catalog/pg_collation.c

@@ -14,6 +14,7 @@
  */
 #include "postgres.h"
 
+#include "access/genam.h"
 #include "access/heapam.h"
 #include "access/sysattr.h"
 #include "catalog/dependency.h"
@@ -22,16 +23,13 @@
 #include "catalog/pg_collation.h"
 #include "catalog/pg_collation_fn.h"
 #include "catalog/pg_namespace.h"
-#include "catalog/pg_proc.h"
 #include "mb/pg_wchar.h"
-#include "miscadmin.h"
-#include "utils/acl.h"
 #include "utils/builtins.h"
 #include "utils/fmgroids.h"
-#include "utils/rel.h"
 #include "utils/syscache.h"
 #include "utils/tqual.h"
 
+
 /*
  * CollationCreate
  *
@@ -43,12 +41,11 @@ CollationCreate(const char *collname, Oid collnamespace,
 				int32 collencoding,
 				const char *collcollate, const char *collctype)
 {
-	int			i;
 	Relation	rel;
 	TupleDesc	tupDesc;
 	HeapTuple	tup;
-	bool		nulls[Natts_pg_collation];
 	Datum		values[Natts_pg_collation];
+	bool		nulls[Natts_pg_collation];
 	NameData	name_name, name_collate, name_ctype;
 	Oid			oid;
 	ObjectAddress myself,
@@ -60,7 +57,13 @@ CollationCreate(const char *collname, Oid collnamespace,
 	AssertArg(collcollate);
 	AssertArg(collctype);
 
-	/* make sure there is no existing collation of same name */
+	/*
+	 * Make sure there is no existing collation of same name & encoding.
+	 *
+	 * This would be caught by the unique index anyway; we're just giving
+	 * a friendlier error message.  The unique index provides a backstop
+	 * against race conditions.
+	 */
 	if (SearchSysCacheExists3(COLLNAMEENCNSP,
 							  PointerGetDatum(collname),
 							  Int32GetDatum(collencoding),
@@ -70,18 +73,27 @@ CollationCreate(const char *collname, Oid collnamespace,
 				 errmsg("collation \"%s\" for encoding \"%s\" already exists",
 						collname, pg_encoding_to_char(collencoding))));
 
+	/*
+	 * Also forbid matching an any-encoding entry.  This test of course is
+	 * not backed up by the unique index, but it's not a problem since we
+	 * don't support adding any-encoding entries after initdb.
+	 */
+	if (SearchSysCacheExists3(COLLNAMEENCNSP,
+							  PointerGetDatum(collname),
+							  Int32GetDatum(-1),
+							  ObjectIdGetDatum(collnamespace)))
+		ereport(ERROR,
+				(errcode(ERRCODE_DUPLICATE_OBJECT),
+				 errmsg("collation \"%s\" already exists",
+						collname)));
+
 	/* open pg_collation */
 	rel = heap_open(CollationRelationId, RowExclusiveLock);
-	tupDesc = rel->rd_att;
-
-	/* initialize nulls and values */
-	for (i = 0; i < Natts_pg_collation; i++)
-	{
-		nulls[i] = false;
-		values[i] = (Datum) NULL;
-	}
+	tupDesc = RelationGetDescr(rel);
 
 	/* form a tuple */
+	memset(nulls, 0, sizeof(nulls));
+
 	namestrcpy(&name_name, collname);
 	values[Anum_pg_collation_collname - 1] = NameGetDatum(&name_name);
 	values[Anum_pg_collation_collnamespace - 1] = ObjectIdGetDatum(collnamespace);
@@ -101,8 +113,9 @@ CollationCreate(const char *collname, Oid collnamespace,
 	/* update the index if any */
 	CatalogUpdateIndexes(rel, tup);
 
+	/* set up dependencies for the new collation */
 	myself.classId = CollationRelationId;
-	myself.objectId = HeapTupleGetOid(tup);
+	myself.objectId = oid;
 	myself.objectSubId = 0;
 
 	/* create dependency on namespace */
@@ -120,7 +133,7 @@ CollationCreate(const char *collname, Oid collnamespace,
 
 	/* Post creation hook for new collation */
 	InvokeObjectAccessHook(OAT_POST_CREATE,
-						   CollationRelationId, HeapTupleGetOid(tup), 0);
+						   CollationRelationId, oid, 0);
 
 	heap_freetuple(tup);
 	heap_close(rel, RowExclusiveLock);
@@ -138,26 +151,28 @@ void
 RemoveCollationById(Oid collationOid)
 {
 	Relation	rel;
-	HeapTuple	tuple;
-	HeapScanDesc scan;
 	ScanKeyData scanKeyData;
+	SysScanDesc scandesc;
+	HeapTuple	tuple;
+
+	rel = heap_open(CollationRelationId, RowExclusiveLock);
 
 	ScanKeyInit(&scanKeyData,
 				ObjectIdAttributeNumber,
 				BTEqualStrategyNumber, F_OIDEQ,
 				ObjectIdGetDatum(collationOid));
 
-	/* open pg_collation */
-	rel = heap_open(CollationRelationId, RowExclusiveLock);
+	scandesc = systable_beginscan(rel, CollationOidIndexId, true,
+								  SnapshotNow, 1, &scanKeyData);
 
-	scan = heap_beginscan(rel, SnapshotNow,
-						  1, &scanKeyData);
+	tuple = systable_getnext(scandesc);
 
-	/* search for the target tuple */
-	if (HeapTupleIsValid(tuple = heap_getnext(scan, ForwardScanDirection)))
+	if (HeapTupleIsValid(tuple))
 		simple_heap_delete(rel, &tuple->t_self);
 	else
 		elog(ERROR, "could not find tuple for collation %u", collationOid);
-	heap_endscan(scan);
+
+	systable_endscan(scandesc);
+
 	heap_close(rel, RowExclusiveLock);
 }

src/backend/commands/collationcmds.c

@@ -1,7 +1,7 @@
 /*-------------------------------------------------------------------------
  *
  * collationcmds.c
- *	  collation creation command support code
+ *	  collation-related commands support code
  *
  * Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
@@ -27,7 +27,6 @@
 #include "commands/defrem.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
-#include "parser/parse_type.h"
 #include "utils/acl.h"
 #include "utils/builtins.h"
 #include "utils/lsyscache.h"
@@ -134,11 +133,11 @@ DefineCollation(List *names, List *parameters)
 	check_encoding_locale_matches(GetDatabaseEncoding(), collcollate, collctype);
 
 	newoid = CollationCreate(collName,
-					collNamespace,
-					GetUserId(),
-					GetDatabaseEncoding(),
-					collcollate,
-					collctype);
+							 collNamespace,
+							 GetUserId(),
+							 GetDatabaseEncoding(),
+							 collcollate,
+							 collctype);
 
 	/* check that the locales can be loaded */
 	CommandCounterIncrement();
@@ -235,11 +234,22 @@ RenameCollation(List *name, const char *newname)
 							  ObjectIdGetDatum(namespaceOid)))
 		ereport(ERROR,
 				(errcode(ERRCODE_DUPLICATE_OBJECT),
-				 errmsg("collation \"%s\" for current database encoding \"%s\" already exists in schema \"%s\"",
+				 errmsg("collation \"%s\" for encoding \"%s\" already exists in schema \"%s\"",
 						newname,
 						GetDatabaseEncodingName(),
 						get_namespace_name(namespaceOid))));
 
+	/* mustn't match an any-encoding entry, either */
+	if (SearchSysCacheExists3(COLLNAMEENCNSP,
+							  CStringGetDatum(newname),
+							  Int32GetDatum(-1),
+							  ObjectIdGetDatum(namespaceOid)))
+		ereport(ERROR,
+				(errcode(ERRCODE_DUPLICATE_OBJECT),
+				 errmsg("collation \"%s\" already exists in schema \"%s\"",
+						newname,
+						get_namespace_name(namespaceOid))));
+
 	/* must be owner */
 	if (!pg_collation_ownercheck(collationOid, GetUserId()))
 		aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_COLLATION,
@@ -256,8 +266,9 @@ RenameCollation(List *name, const char *newname)
 	simple_heap_update(rel, &tup->t_self, tup);
 	CatalogUpdateIndexes(rel, tup);
 
-	heap_close(rel, NoLock);
 	heap_freetuple(tup);
+
+	heap_close(rel, RowExclusiveLock);
 }
 
 /*
@@ -275,7 +286,7 @@ AlterCollationOwner(List *name, Oid newOwnerId)
 
 	AlterCollationOwner_internal(rel, collationOid, newOwnerId);
 
-	heap_close(rel, NoLock);
+	heap_close(rel, RowExclusiveLock);
 }
 
 /*
@@ -290,7 +301,7 @@ AlterCollationOwner_oid(Oid collationOid, Oid newOwnerId)
 
 	AlterCollationOwner_internal(rel, collationOid, newOwnerId);
 
-	heap_close(rel, NoLock);
+	heap_close(rel, RowExclusiveLock);
 }
 
 /*
@@ -364,24 +375,14 @@ AlterCollationOwner_internal(Relation rel, Oid collationOid, Oid newOwnerId)
 void
 AlterCollationNamespace(List *name, const char *newschema)
 {
-	Oid			collOid, nspOid;
-	Relation	rel;
-
-	rel = heap_open(CollationRelationId, RowExclusiveLock);
+	Oid			collOid,
+				nspOid;
 
 	collOid = get_collation_oid(name, false);
 
-	/* get schema OID */
 	nspOid = LookupCreationNamespace(newschema);
 
-	AlterObjectNamespace(rel, COLLOID, -1,
-						 collOid, nspOid,
-						 Anum_pg_collation_collname,
-						 Anum_pg_collation_collnamespace,
-						 Anum_pg_collation_collowner,
-						 ACL_KIND_COLLATION);
-
-	heap_close(rel, NoLock);
+	AlterCollationNamespace_oid(collOid, nspOid);
 }
 
 /*
@@ -392,9 +393,43 @@ AlterCollationNamespace_oid(Oid collOid, Oid newNspOid)
 {
 	Oid         oldNspOid;
 	Relation	rel;
+	char	   *collation_name;
 
 	rel = heap_open(CollationRelationId, RowExclusiveLock);
 
+	/*
+	 * We have to check for name collision ourselves, because
+	 * AlterObjectNamespace doesn't know how to deal with the encoding
+	 * considerations.
+	 */
+	collation_name = get_collation_name(collOid);
+	if (!collation_name)
+		elog(ERROR, "cache lookup failed for collation %u", collOid);
+
+	/* make sure the name doesn't already exist in new schema */
+	if (SearchSysCacheExists3(COLLNAMEENCNSP,
+							  CStringGetDatum(collation_name),
+							  Int32GetDatum(GetDatabaseEncoding()),
+							  ObjectIdGetDatum(newNspOid)))
+		ereport(ERROR,
+				(errcode(ERRCODE_DUPLICATE_OBJECT),
+				 errmsg("collation \"%s\" for encoding \"%s\" already exists in schema \"%s\"",
+						collation_name,
+						GetDatabaseEncodingName(),
+						get_namespace_name(newNspOid))));
+
+	/* mustn't match an any-encoding entry, either */
+	if (SearchSysCacheExists3(COLLNAMEENCNSP,
+							  CStringGetDatum(collation_name),
+							  Int32GetDatum(-1),
+							  ObjectIdGetDatum(newNspOid)))
+		ereport(ERROR,
+				(errcode(ERRCODE_DUPLICATE_OBJECT),
+				 errmsg("collation \"%s\" already exists in schema \"%s\"",
+						collation_name,
+						get_namespace_name(newNspOid))));
+
+	/* OK, do the work */
 	oldNspOid = AlterObjectNamespace(rel, COLLOID, -1,
 									 collOid, newNspOid,
 									 Anum_pg_collation_collname,