Attached patch gets rid of the global timezone in the following steps:

* Changes the APIs to the timezone functions to take a pg_tz pointer as
an argument, representing the timezone to use for the selected
operation.

* Adds a global_timezone variable that represents the current timezone
in the backend as set by SET TIMEZONE (or guc, or env, etc).

* Implements a hash-table cache of loaded tables, so we don't have to
read and parse the TZ file everytime we change a timezone. While not
necesasry now (we don't change timezones very often), I beleive this
will be necessary (or at least good) when "multiple timezones in the
same query" is eventually implemented. And code-wise, this was the time
to do it.


There are no user-visible changes at this time. Implementing the
"multiple zones in one query" is a later step...

This also gets rid of some of the cruft needed to "back out a timezone
change", since we previously couldn't check a timezone unless it was
activated first.

Passes regression tests on win32, linux (slackware 10) and solaris x86.

Magnus Hagander

src/backend/utils/adt/datetime.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/datetime.c,v 1.137 2005/01/11 18:33:45 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/datetime.c,v 1.138 2005/04/19 03:13:59 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1634,7 +1634,8 @@ DetermineLocalTimeZone(struct pg_tm * tm)
 	res = pg_next_dst_boundary(&prevtime,
 							   &before_gmtoff, &before_isdst,
 							   &boundary,
-							   &after_gmtoff, &after_isdst);
+							   &after_gmtoff, &after_isdst,
+		                       global_timezone);
 	if (res < 0)
 		goto overflow;			/* failure? */