Force pg_database updates out to disk immediately after ALTER DATABASE;

this is to avoid scenarios where incoming backends find no live copies
of a database's row because the only live copy is in an as-yet-unwritten
shared buffer, which they can't see.  Also, use FlushRelationBuffers()
for forcing out pg_database, instead of the much more expensive BufferSync().
There's no need to write out pages belonging to other relations.

diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index a74ad9b2f0720b655c7b976c4efd36fc7a874a78..6d0fa6a13d453b6cd93cadca0c874db103a40c79 100644 (file)
--- 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 1.146 2004/10/28 00:39:58 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/commands/dbcommands.c,v 1.147 2004/11/18 01:14:26 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -330,7 +330,7 @@ createdb(const CreatedbStmt *stmt)
        /*
         * Force dirty buffers out to disk, to ensure source database is
         * up-to-date for the copy.  (We really only need to flush buffers for
-        * the source database...)
+        * the source database, but bufmgr.c provides no API for that.)
         */
        BufferSync(-1, -1);
 
@@ -497,15 +497,15 @@ createdb(const CreatedbStmt *stmt)
        /* Update indexes */
        CatalogUpdateIndexes(pg_database_rel, tuple);
 
-       /* Close pg_database, but keep lock till commit */
-       heap_close(pg_database_rel, NoLock);
-
        /*
         * Force dirty buffers out to disk, so that newly-connecting backends
         * will see the new database in pg_database right away.  (They'll see
         * an uncommitted tuple, but they don't care; see GetRawDatabaseInfo.)
         */
-       BufferSync(-1, -1);
+       FlushRelationBuffers(pg_database_rel, MaxBlockNumber);
+
+       /* Close pg_database, but keep exclusive lock till commit */
+       heap_close(pg_database_rel, NoLock);
 }
 
 
@@ -607,12 +607,6 @@ dropdb(const char *dbname)
         */
        DeleteComments(db_id, RelationGetRelid(pgdbrel), 0);
 
-       /*
-        * Close pg_database, but keep exclusive lock till commit to ensure
-        * that any new backend scanning pg_database will see the tuple dead.
-        */
-       heap_close(pgdbrel, NoLock);
-
        /*
         * Drop pages for this database that are in the shared buffer cache.
         * This is important to ensure that no remaining backend tries to
@@ -644,7 +638,10 @@ dropdb(const char *dbname)
         * (They'll see an uncommitted deletion, but they don't care; see
         * GetRawDatabaseInfo.)
         */
-       BufferSync(-1, -1);
+       FlushRelationBuffers(pgdbrel, MaxBlockNumber);
+
+       /* Close pg_database, but keep exclusive lock till commit */
+       heap_close(pgdbrel, NoLock);
 }
 
 
@@ -733,7 +730,6 @@ RenameDatabase(const char *oldname, const char *newname)
        CatalogUpdateIndexes(rel, newtup);
 
        systable_endscan(scan);
-       heap_close(rel, NoLock);
 
        /*
         * Force dirty buffers out to disk, so that newly-connecting backends
@@ -741,7 +737,10 @@ RenameDatabase(const char *oldname, const char *newname)
         * see an uncommitted tuple, but they don't care; see
         * GetRawDatabaseInfo.)
         */
-       BufferSync(-1, -1);
+       FlushRelationBuffers(rel, MaxBlockNumber);
+
+       /* Close pg_database, but keep exclusive lock till commit */
+       heap_close(rel, NoLock);
 }
 
 
@@ -763,7 +762,10 @@ AlterDatabaseSet(AlterDatabaseSetStmt *stmt)
 
        valuestr = flatten_set_variable_args(stmt->variable, stmt->value);
 
-       rel = heap_openr(DatabaseRelationName, RowExclusiveLock);
+       /*
+        * We need AccessExclusiveLock so we can safely do FlushRelationBuffers.
+        */
+       rel = heap_openr(DatabaseRelationName, AccessExclusiveLock);
        ScanKeyInit(&scankey,
                                Anum_pg_database_datname,
                                BTEqualStrategyNumber, F_NAMEEQ,
@@ -821,6 +823,16 @@ AlterDatabaseSet(AlterDatabaseSetStmt *stmt)
        CatalogUpdateIndexes(rel, newtuple);
 
        systable_endscan(scan);
+
+       /*
+        * Force dirty buffers out to disk, so that newly-connecting backends
+        * will see the altered row in pg_database right away.  (They'll
+        * see an uncommitted tuple, but they don't care; see
+        * GetRawDatabaseInfo.)
+        */
+       FlushRelationBuffers(rel, MaxBlockNumber);
+
+       /* Close pg_database, but keep exclusive lock till commit */
        heap_close(rel, NoLock);
 }
 
@@ -837,7 +849,10 @@ AlterDatabaseOwner(const char *dbname, AclId newOwnerSysId)
        SysScanDesc scan;
        Form_pg_database datForm;
 
-       rel = heap_openr(DatabaseRelationName, RowExclusiveLock);
+       /*
+        * We need AccessExclusiveLock so we can safely do FlushRelationBuffers.
+        */
+       rel = heap_openr(DatabaseRelationName, AccessExclusiveLock);
        ScanKeyInit(&scankey,
                                Anum_pg_database_datname,
                                BTEqualStrategyNumber, F_NAMEEQ,
@@ -901,9 +916,22 @@ AlterDatabaseOwner(const char *dbname, AclId newOwnerSysId)
                CatalogUpdateIndexes(rel, newtuple);
 
                heap_freetuple(newtuple);
+
+               /* must release buffer pins before FlushRelationBuffers */
+               systable_endscan(scan);
+
+               /*
+                * Force dirty buffers out to disk, so that newly-connecting backends
+                * will see the altered row in pg_database right away.  (They'll
+                * see an uncommitted tuple, but they don't care; see
+                * GetRawDatabaseInfo.)
+                */
+               FlushRelationBuffers(rel, MaxBlockNumber);
        }
+       else
+               systable_endscan(scan);
 
-       systable_endscan(scan);
+       /* Close pg_database, but keep exclusive lock till commit */
        heap_close(rel, NoLock);
 }
 
@@ -1176,7 +1204,7 @@ dbase_redo(XLogRecPtr lsn, XLogRecord *record)
                /*
                 * Force dirty buffers out to disk, to ensure source database is
                 * up-to-date for the copy.  (We really only need to flush buffers for
-                * the source database...)
+                * the source database, but bufmgr.c provides no API for that.)
                 */
                BufferSync(-1, -1);