Add code to prevent transaction ID wraparound by enforcing a safe limit

in GetNewTransactionId().  Since the limit value has to be computed
before we run any real transactions, this requires adding code to database
startup to scan pg_database and determine the oldest datfrozenxid.
This can conveniently be combined with the first stage of an attack on
the problem that the 'flat file' copies of pg_shadow and pg_group are
not properly updated during WAL recovery.  The code I've added to
startup resides in a new file src/backend/utils/init/flatfiles.c, and
it is responsible for rewriting the flat files as well as initializing
the XID wraparound limit value.  This will eventually allow us to get
rid of GetRawDatabaseInfo too, but we'll need an initdb so we can add
a trigger to pg_database.

1 files changed, 27 insertions, 1 deletions

diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index e5a2a0bcd31..0962e32c5e1 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/dbcommands.c,v 1.149 2005/01/27 23:23:55 neilc Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/dbcommands.c,v 1.150 2005/02/20 02:21:34 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -39,6 +39,7 @@
 #include "utils/acl.h"
 #include "utils/array.h"
 #include "utils/builtins.h"
+#include "utils/flatfiles.h"
 #include "utils/fmgroids.h"
 #include "utils/guc.h"
 #include "utils/lsyscache.h"
@@ -506,6 +507,11 @@ createdb(const CreatedbStmt *stmt)
 
 	/* Close pg_database, but keep exclusive lock till commit */
 	heap_close(pg_database_rel, NoLock);
+
+	/*
+	 * Set flag to update flat database file at commit.
+	 */
+	database_file_update_needed();
 }
 
 
@@ -642,6 +648,11 @@ dropdb(const char *dbname)
 
 	/* Close pg_database, but keep exclusive lock till commit */
 	heap_close(pgdbrel, NoLock);
+
+	/*
+	 * Set flag to update flat database file at commit.
+	 */
+	database_file_update_needed();
 }
 
 
@@ -741,6 +752,11 @@ RenameDatabase(const char *oldname, const char *newname)
 
 	/* Close pg_database, but keep exclusive lock till commit */
 	heap_close(rel, NoLock);
+
+	/*
+	 * Set flag to update flat database file at commit.
+	 */
+	database_file_update_needed();
 }
 
 
@@ -834,6 +850,11 @@ AlterDatabaseSet(AlterDatabaseSetStmt *stmt)
 
 	/* Close pg_database, but keep exclusive lock till commit */
 	heap_close(rel, NoLock);
+
+	/*
+	 * We don't bother updating the flat file since ALTER DATABASE SET
+	 * doesn't affect it.
+	 */
 }
 
 
@@ -933,6 +954,11 @@ AlterDatabaseOwner(const char *dbname, AclId newOwnerSysId)
 
 	/* Close pg_database, but keep exclusive lock till commit */
 	heap_close(rel, NoLock);
+
+	/*
+	 * We don't bother updating the flat file since ALTER DATABASE OWNER
+	 * doesn't affect it.
+	 */
 }