Insert CHECK_FOR_INTERRUPTS calls into loops in dbsize.c, to ensure that

the various disk-size-reporting functions will respond to query cancel
reasonably promptly even in very large databases.  Per report from
Kevin Grittner.

src/backend/utils/adt/dbsize.c

@@ -5,7 +5,7 @@
  * Copyright (c) 2002-2010, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/dbsize.c,v 1.27 2010/01/19 05:50:18 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/dbsize.c,v 1.28 2010/01/23 21:29:00 tgl Exp $
  *
  */
 
@@ -46,6 +46,8 @@ db_dir_size(const char *path)
 	{
 		struct stat fst;
 
+		CHECK_FOR_INTERRUPTS();
+
 		if (strcmp(direntry->d_name, ".") == 0 ||
 			strcmp(direntry->d_name, "..") == 0)
 			continue;
@@ -104,6 +106,8 @@ calculate_database_size(Oid dbOid)
 
 	while ((direntry = ReadDir(dirdesc, dirpath)) != NULL)
 	{
+		CHECK_FOR_INTERRUPTS();
+
 		if (strcmp(direntry->d_name, ".") == 0 ||
 			strcmp(direntry->d_name, "..") == 0)
 			continue;
@@ -194,6 +198,8 @@ calculate_tablespace_size(Oid tblspcOid)
 	{
 		struct stat fst;
 
+		CHECK_FOR_INTERRUPTS();
+
 		if (strcmp(direntry->d_name, ".") == 0 ||
 			strcmp(direntry->d_name, "..") == 0)
 			continue;
@@ -262,6 +268,8 @@ calculate_relation_size(RelFileNode *rfn, ForkNumber forknum)
 	{
 		struct stat fst;
 
+		CHECK_FOR_INTERRUPTS();
+
 		if (segcount == 0)
 			snprintf(pathname, MAXPGPATH, "%s",
 					 relationpath);