Rethink method for assigning OIDs to the template0 and postgres DBs.

Commit aa01051 assigned fixed OIDs to template0 and postgres
in a very ad-hoc way.  Notably, instead of teaching Catalog.pm
about these OIDs, the unused_oids script was just hacked to
not show them as unused.  That's problematic since, for example,
duplicate_oids wouldn't report any future conflict.  Hence,
invent a macro DECLARE_OID_DEFINING_MACRO() that can be used to
define an OID that is known to Catalog.pm and will participate
in duplicate-detection as well as renumbering by renumber_oids.pl.
(We don't anticipate renumbering these particular OIDs, but we
might as well build out all the Catalog.pm infrastructure while
we're here.)

Another issue is that aa01051 neglected to touch IsPinnedObject,
with the result that it now claimed template0 and postgres are
pinned.  The right thing to do there seems to be to teach it that
no database is pinned, since in fact DROP DATABASE doesn't check
for pinned-ness (and at least for these cases, that is an
intentional choice).  It's not clear whether this wrong answer
had any visible effect, but perhaps it could have resulted in
erroneous management of dependency entries.

In passing, rename the TemplateDbOid macro to Template1DbOid
to reduce confusion (likely we should have done that way back
when we invented template0, but we didn't), and rename the
OID macros for template0 and postgres to have a similar style.

There are no changes to postgres.bki here, so no need for a
catversion bump.

Discussion: https://postgr.es/m/2935358.1650479692@sss.pgh.pa.us

Author: tglsfdc

doc/src/sgml/bki.sgml

@@ -180,12 +180,13 @@
 [
 
 # A comment could appear here.
-{ oid => '1', oid_symbol => 'TemplateDbOid',
+{ oid => '1', oid_symbol => 'Template1DbOid',
   descr => 'database\'s default template',
-  datname => 'template1', encoding => 'ENCODING', datistemplate => 't',
+  datname => 'template1', encoding => 'ENCODING',
+  datlocprovider => 'LOCALE_PROVIDER', datistemplate => 't',
   datallowconn => 't', datconnlimit => '-1', datfrozenxid => '0',
   datminmxid => '1', dattablespace => 'pg_default', datcollate => 'LC_COLLATE',
-  datctype => 'LC_CTYPE', datacl => '_null_' },
+  datctype => 'LC_CTYPE', daticulocale => 'ICU_LOCALE', datacl => '_null_' },
 
 ]
 ]]></programlisting>

src/backend/access/transam/xlog.c

@@ -4540,9 +4540,9 @@ BootStrapXLOG(void)
 	checkPoint.nextMulti = FirstMultiXactId;
 	checkPoint.nextMultiOffset = 0;
 	checkPoint.oldestXid = FirstNormalTransactionId;
-	checkPoint.oldestXidDB = TemplateDbOid;
+	checkPoint.oldestXidDB = Template1DbOid;
 	checkPoint.oldestMulti = FirstMultiXactId;
-	checkPoint.oldestMultiDB = TemplateDbOid;
+	checkPoint.oldestMultiDB = Template1DbOid;
 	checkPoint.oldestCommitTsXid = InvalidTransactionId;
 	checkPoint.newestCommitTsXid = InvalidTransactionId;
 	checkPoint.time = (pg_time_t) time(NULL);

src/backend/catalog/Catalog.pm

@@ -44,6 +44,8 @@ sub ParseHeader
 	$catalog{columns}     = [];
 	$catalog{toasting}    = [];
 	$catalog{indexing}    = [];
+	$catalog{other_oids}  = [];
+	$catalog{foreign_keys} = [];
 	$catalog{client_code} = [];
 
 	open(my $ifh, '<', $input_file) || die "$input_file: $!";
@@ -118,6 +120,14 @@ sub ParseHeader
 				index_decl => $6
 			  };
 		}
+		elsif (/^DECLARE_OID_DEFINING_MACRO\(\s*(\w+),\s*(\d+)\)/)
+		{
+			push @{ $catalog{other_oids} },
+			  {
+				other_name => $1,
+				other_oid  => $2
+			  };
+		}
 		elsif (
 			/^DECLARE_(ARRAY_)?FOREIGN_KEY(_OPT)?\(\s*\(([^)]+)\),\s*(\w+),\s*\(([^)]+)\)\)/
 		  )
@@ -572,6 +582,10 @@ sub FindAllOidsFromHeaders
 		{
 			push @oids, $index->{index_oid};
 		}
+		foreach my $other (@{ $catalog->{other_oids} })
+		{
+			push @oids, $other->{other_oid};
+		}
 	}
 
 	return \@oids;

src/backend/catalog/catalog.c

@@ -339,16 +339,20 @@ IsPinnedObject(Oid classId, Oid objectId)
 	 * robustness.
 	 */
 
-	/* template1 is not pinned */
-	if (classId == DatabaseRelationId &&
-		objectId == TemplateDbOid)
-		return false;
-
 	/* the public namespace is not pinned */
 	if (classId == NamespaceRelationId &&
 		objectId == PG_PUBLIC_NAMESPACE)
 		return false;
 
+	/*
+	 * Databases are never pinned.  It might seem that it'd be prudent to pin
+	 * at least template0; but we do this intentionally so that template0 and
+	 * template1 can be rebuilt from each other, thus letting them serve as
+	 * mutual backups (as long as you've not modified template1, anyway).
+	 */
+	if (classId == DatabaseRelationId)
+		return false;
+
 	/*
 	 * All other initdb-created objects are pinned.  This is overkill (the
 	 * system doesn't really depend on having every last weird datatype, for

src/backend/catalog/genbki.pl

@@ -472,7 +472,7 @@
 	  $catalog->{rowtype_oid_macro}, $catalog->{rowtype_oid}
 	  if $catalog->{rowtype_oid_macro};
 
-	# Likewise for macros for toast and index OIDs
+	# Likewise for macros for toast, index, and other OIDs
 	foreach my $toast (@{ $catalog->{toasting} })
 	{
 		printf $def "#define %s %s\n",
@@ -488,6 +488,12 @@
 		  $index->{index_oid_macro}, $index->{index_oid}
 		  if $index->{index_oid_macro};
 	}
+	foreach my $other (@{ $catalog->{other_oids} })
+	{
+		printf $def "#define %s %s\n",
+		  $other->{other_name}, $other->{other_oid}
+		  if $other->{other_name};
+	}
 
 	print $def "\n";
 

src/backend/utils/init/postinit.c

@@ -908,7 +908,7 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
 	 */
 	if (bootstrap)
 	{
-		MyDatabaseId = TemplateDbOid;
+		MyDatabaseId = Template1DbOid;
 		MyDatabaseTableSpace = DEFAULTTABLESPACE_OID;
 	}
 	else if (in_dbname != NULL)

src/bin/initdb/initdb.c

@@ -59,11 +59,11 @@
 #include "sys/mman.h"
 #endif
 
-#include "access/transam.h"
 #include "access/xlog_internal.h"
 #include "catalog/pg_authid_d.h"
 #include "catalog/pg_class_d.h" /* pgrminclude ignore */
 #include "catalog/pg_collation_d.h"
+#include "catalog/pg_database_d.h"	/* pgrminclude ignore */
 #include "common/file_perm.h"
 #include "common/file_utils.h"
 #include "common/logging.h"
@@ -1812,8 +1812,8 @@ make_template0(FILE *cmdfd)
 	 * be a little bit slower and make the new cluster a little bit bigger.
 	 */
 	static const char *const template0_setup[] = {
-		"CREATE DATABASE template0 IS_TEMPLATE = true ALLOW_CONNECTIONS = false OID = "
-		CppAsString2(Template0ObjectId)
+		"CREATE DATABASE template0 IS_TEMPLATE = true ALLOW_CONNECTIONS = false"
+		" OID = " CppAsString2(Template0DbOid)
 		" STRATEGY = file_copy;\n\n",
 
 		/*
@@ -1862,7 +1862,8 @@ make_postgres(FILE *cmdfd)
 	 * OID to postgres and select the file_copy strategy.
 	 */
 	static const char *const postgres_setup[] = {
-		"CREATE DATABASE postgres OID = " CppAsString2(PostgresObjectId) " STRATEGY = file_copy;\n\n",
+		"CREATE DATABASE postgres OID = " CppAsString2(PostgresDbOid)
+		" STRATEGY = file_copy;\n\n",
 		"COMMENT ON DATABASE postgres IS 'default administrative connection database';\n\n",
 		NULL
 	};

src/bin/pg_dump/pg_dump.c

@@ -2901,10 +2901,11 @@ dumpDatabase(Archive *fout)
 	qdatname = pg_strdup(fmtId(datname));
 
 	/*
-	 * Prepare the CREATE DATABASE command.  We must specify encoding, locale,
-	 * and tablespace since those can't be altered later.  Other DB properties
-	 * are left to the DATABASE PROPERTIES entry, so that they can be applied
-	 * after reconnecting to the target DB.
+	 * Prepare the CREATE DATABASE command.  We must specify OID (if we want
+	 * to preserve that), as well as the encoding, locale, and tablespace
+	 * since those can't be altered later.  Other DB properties are left to
+	 * the DATABASE PROPERTIES entry, so that they can be applied after
+	 * reconnecting to the target DB.
 	 */
 	if (dopt->binary_upgrade)
 	{

src/include/access/transam.h

@@ -196,10 +196,6 @@ FullTransactionIdAdvance(FullTransactionId *dest)
 #define FirstUnpinnedObjectId	12000
 #define FirstNormalObjectId		16384
 
-/* OIDs of Template0 and Postgres database are fixed */
-#define Template0ObjectId		4
-#define PostgresObjectId		5
-
 /*
  * VariableCache is a data structure in shared memory that is used to track
  * OID and XID assignment state.  For largely historical reasons, there is

src/include/catalog/genbki.h

@@ -84,6 +84,14 @@
 #define DECLARE_UNIQUE_INDEX(name,oid,oidmacro,decl) extern int no_such_variable
 #define DECLARE_UNIQUE_INDEX_PKEY(name,oid,oidmacro,decl) extern int no_such_variable
 
+/*
+ * These lines inform genbki.pl about manually-assigned OIDs that do not
+ * correspond to any entry in the catalog *.dat files, but should be subject
+ * to uniqueness verification and renumber_oids.pl renumbering.  A C macro
+ * to #define the given name is emitted into the corresponding *_d.h file.
+ */
+#define DECLARE_OID_DEFINING_MACRO(name,oid) extern int no_such_variable
+
 /*
  * These lines are processed by genbki.pl to create a table for use
  * by the pg_get_catalog_foreign_keys() function.  We do not have any

src/include/catalog/pg_database.dat

@@ -12,7 +12,7 @@
 
 [
 
-{ oid => '1', oid_symbol => 'TemplateDbOid',
+{ oid => '1', oid_symbol => 'Template1DbOid',
   descr => 'default template for new databases',
   datname => 'template1', encoding => 'ENCODING', datlocprovider => 'LOCALE_PROVIDER', datistemplate => 't',
   datallowconn => 't', datconnlimit => '-1', datfrozenxid => '0',

src/include/catalog/pg_database.h

@@ -91,4 +91,13 @@ DECLARE_TOAST_WITH_MACRO(pg_database, 4177, 4178, PgDatabaseToastTable, PgDataba
 DECLARE_UNIQUE_INDEX(pg_database_datname_index, 2671, DatabaseNameIndexId, on pg_database using btree(datname name_ops));
 DECLARE_UNIQUE_INDEX_PKEY(pg_database_oid_index, 2672, DatabaseOidIndexId, on pg_database using btree(oid oid_ops));
 
+/*
+ * pg_database.dat contains an entry for template1, but not for the template0
+ * or postgres databases, because those are created later in initdb.
+ * However, we still want to manually assign the OIDs for template0 and
+ * postgres, so declare those here.
+ */
+DECLARE_OID_DEFINING_MACRO(Template0DbOid, 4);
+DECLARE_OID_DEFINING_MACRO(PostgresDbOid, 5);
+
 #endif							/* PG_DATABASE_H */

src/include/catalog/renumber_oids.pl

@@ -170,6 +170,16 @@
 				$changed = 1;
 			}
 		}
+		elsif (/^(DECLARE_OID_DEFINING_MACRO\(\s*\w+,\s*)(\d+)\)/)
+		{
+			if (exists $maphash{$2})
+			{
+				my $repl = $1 . $maphash{$2} . ")";
+				$line =~
+				  s/^DECLARE_OID_DEFINING_MACRO\(\s*\w+,\s*\d+\)/$repl/;
+				$changed = 1;
+			}
+		}
 		elsif ($line =~ m/^CATALOG\((\w+),(\d+),(\w+)\)/)
 		{
 			if (exists $maphash{$2})

src/include/catalog/unused_oids

@@ -32,15 +32,6 @@ my @input_files = glob("pg_*.h");
 
 my $oids = Catalog::FindAllOidsFromHeaders(@input_files);
 
-# Push the template0 and postgres database OIDs.
-my $Template0ObjectId =
-  Catalog::FindDefinedSymbol('access/transam.h', '..', 'Template0ObjectId');
-push @{$oids}, $Template0ObjectId;
-
-my $PostgresObjectId =
-  Catalog::FindDefinedSymbol('access/transam.h', '..', 'PostgresObjectId');
-push @{$oids}, $PostgresObjectId;
-
 # Also push FirstGenbkiObjectId to serve as a terminator for the last gap.
 my $FirstGenbkiObjectId =
   Catalog::FindDefinedSymbol('access/transam.h', '..', 'FirstGenbkiObjectId');