Force a checkpoint in CREATE DATABASE before starting to copy the files,

to process any pending unlinks for the source database.

Before, if you dropped a relation in the template database just before
CREATE DATABASE, and a checkpoint happened during copydir(), the checkpoint
might delete a file that we're just about to copy, causing lstat() in
copydir() to fail with ENOENT.

Backpatch to 8.3, where the pending unlinks were introduced.

Per report by Matthew Wakeling and analysis by Tom Lane.

src/backend/commands/dbcommands.c

@@ -13,7 +13,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/dbcommands.c,v 1.213 2008/09/30 10:52:12 heikki Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/dbcommands.c,v 1.214 2008/10/09 10:34:06 heikki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -539,10 +539,15 @@ createdb(const CreatedbStmt *stmt)
 	copyTemplateDependencies(src_dboid, dboid);
 
 	/*
-	 * Force dirty buffers out to disk, to ensure source database is
-	 * up-to-date for the copy.
+	 * Force a checkpoint before starting the copy. This will force dirty
+	 * buffers out to disk, to ensure source database is up-to-date on disk
+	 * for the copy. FlushDatabaseBuffers() would suffice for that, but we
+	 * also want to process any pending unlink requests. Otherwise, if a
+	 * checkpoint happened while we're copying files, a file might be deleted
+	 * just when we're about to copy it, causing the lstat() call in copydir()
+	 * to fail with ENOENT.
 	 */
-	FlushDatabaseBuffers(src_dboid);
+	RequestCheckpoint(CHECKPOINT_IMMEDIATE | CHECKPOINT_FORCE | CHECKPOINT_WAIT);
 
 	/*
 	 * Once we start copying subdirectories, we need to be able to clean 'em