From ca4af308c32d03db5fbacb54d6e583ceb904f268 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri, 9 Sep 2011 17:59:11 -0400
Subject: [PATCH] Simplify handling of the timezone GUC by making initdb choose
 the default.

We were doing some amazingly complicated things in order to avoid running
the very expensive identify_system_timezone() procedure during GUC
initialization.  But there is an obvious fix for that, which is to do it
once during initdb and have initdb install the system-specific default into
postgresql.conf, as it already does for most other GUC variables that need
system-environment-dependent defaults.  This means that the timezone (and
log_timezone) settings no longer have any magic behavior in the server.
Per discussion.
---
 doc/src/sgml/config.sgml                      |   14 +-
 doc/src/sgml/datatype.sgml                    |   21 +-
 doc/src/sgml/ref/set.sgml                     |    4 +-
 src/backend/bootstrap/bootstrap.c             |    4 -
 src/backend/commands/variable.c               |   43 +-
 src/backend/postmaster/postmaster.c           |   15 -
 src/backend/tcop/postgres.c                   |    4 -
 src/backend/utils/error/elog.c                |   29 +-
 src/backend/utils/misc/guc-file.l             |    1 -
 src/backend/utils/misc/guc.c                  |   21 +-
 src/backend/utils/misc/postgresql.conf.sample |    4 +-
 src/bin/initdb/.gitignore                     |    1 +
 src/bin/initdb/Makefile                       |   11 +-
 src/bin/initdb/findtimezone.c                 | 1224 ++++++++++++++++
 src/bin/initdb/initdb.c                       |   25 +-
 src/include/pgtime.h                          |   23 +-
 src/include/utils/guc.h                       |    2 -
 src/timezone/localtime.c                      |   28 +
 src/timezone/pgtz.c                           | 1265 +----------------
 19 files changed, 1372 insertions(+), 1367 deletions(-)
 create mode 100644 src/bin/initdb/findtimezone.c

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 615b2b078bf..f95f9cc8bd8 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -3915,9 +3915,10 @@ FROM pg_stat_activity;
         Sets the time zone used for timestamps written in the server log.
         Unlike <xref linkend="guc-timezone">, this value is cluster-wide,
         so that all sessions will report timestamps consistently.
-        If not explicitly set, the server initializes this variable to the
-        time zone specified by its system environment.  See <xref
-        linkend="datatype-timezones"> for more information.
+        The built-in default is <literal>GMT</>, but that is typically
+        overridden in <filename>postgresql.conf</>; <application>initdb</>
+        will install a setting there corresponding to its system environment.
+        See <xref linkend="datatype-timezones"> for more information.
         This parameter can only be set in the <filename>postgresql.conf</>
         file or on the server command line.
        </para>
@@ -4963,9 +4964,10 @@ SET XML OPTION { DOCUMENT | CONTENT };
       <listitem>
        <para>
         Sets the time zone for displaying and interpreting time stamps.
-        If not explicitly set, the server initializes this variable to the
-        time zone specified by its system environment.  See <xref
-        linkend="datatype-timezones"> for more information.
+        The built-in default is <literal>GMT</>, but that is typically
+        overridden in <filename>postgresql.conf</>; <application>initdb</>
+        will install a setting there corresponding to its system environment.
+        See <xref linkend="datatype-timezones"> for more information.
        </para>
       </listitem>
      </varlistentry>
diff --git a/doc/src/sgml/datatype.sgml b/doc/src/sgml/datatype.sgml
index 89b531fa1d2..e7b3098f28f 100644
--- a/doc/src/sgml/datatype.sgml
+++ b/doc/src/sgml/datatype.sgml
@@ -2286,7 +2286,7 @@ January 8 04:05:06 1999 PST
     but continue to be prone to arbitrary changes, particularly with
     respect to daylight-savings rules.
     <productname>PostgreSQL</productname> uses the widely-used
-    <literal>zoneinfo</> time zone database for information about
+    <literal>zoneinfo</> (Olson) time zone database for information about
     historical time zone rules.  For times in the future, the assumption
     is that the latest known rules for a given time zone will
     continue to be observed indefinitely far into the future.
@@ -2432,26 +2432,9 @@ January 8 04:05:06 1999 PST
      The <xref linkend="guc-timezone"> configuration parameter can
      be set in the file <filename>postgresql.conf</>, or in any of the
      other standard ways described in <xref linkend="runtime-config">.
-     There are also several special ways to set it:
+     There are also some special ways to set it:
 
      <itemizedlist>
-      <listitem>
-       <para>
-        If <varname>timezone</> is not specified in
-        <filename>postgresql.conf</> or as a server command-line option,
-        the server attempts to use the value of the <envar>TZ</envar>
-        environment variable as the default time zone.  If <envar>TZ</envar>
-        is not defined or is not any of the time zone names known to
-        <productname>PostgreSQL</productname>, the server attempts to
-        determine the operating system's default time zone by checking the
-        behavior of the C library function <literal>localtime()</>.  The
-        default time zone is selected as the closest match among
-        <productname>PostgreSQL</productname>'s known time zones.
-        (These rules are also used to choose the default value of
-        <xref linkend="guc-log-timezone">, if not specified.)
-       </para>
-      </listitem>
-
       <listitem>
        <para>
         The <acronym>SQL</acronym> command <command>SET TIME ZONE</command>
diff --git a/doc/src/sgml/ref/set.sgml b/doc/src/sgml/ref/set.sgml
index 40e1bd4e607..21745db4627 100644
--- a/doc/src/sgml/ref/set.sgml
+++ b/doc/src/sgml/ref/set.sgml
@@ -239,9 +239,7 @@ SELECT setseed(<replaceable>value</replaceable>);
          <listitem>
           <para>
            Set the time zone to your local time zone (that is, the
-           server's default value of <varname>timezone</>; if this
-           has not been explicitly set anywhere, it will be the zone that
-           the server's operating system defaults to).
+           server's default value of <varname>timezone</>).
           </para>
          </listitem>
         </varlistentry>
diff --git a/src/backend/bootstrap/bootstrap.c b/src/backend/bootstrap/bootstrap.c
index e3dd472832e..4fe08df350a 100644
--- a/src/backend/bootstrap/bootstrap.c
+++ b/src/backend/bootstrap/bootstrap.c
@@ -333,10 +333,6 @@ AuxiliaryProcessMain(int argc, char *argv[])
 	{
 		if (!SelectConfigFiles(userDoption, progname))
 			proc_exit(1);
-		/* If timezone is not set, determine what the OS uses */
-		pg_timezone_initialize();
-		/* If timezone_abbreviations is not set, select default */
-		pg_timezone_abbrev_initialize();
 	}
 
 	/* Validate we have been given a reasonable-looking DataDir */
diff --git a/src/backend/commands/variable.c b/src/backend/commands/variable.c
index 239acd07852..87c54b7d480 100644
--- a/src/backend/commands/variable.c
+++ b/src/backend/commands/variable.c
@@ -259,23 +259,6 @@ check_timezone(char **newval, void **extra, GucSource source)
 	char	   *endptr;
 	double		hours;
 
-	if (*newval == NULL)
-	{
-		/*
-		 * The boot_val given for TimeZone in guc.c is NULL.  When we see this
-		 * we just do nothing.	If this isn't overridden from the config file
-		 * then pg_timezone_initialize() will eventually select a default
-		 * value from the environment.	This hack has two purposes: to avoid
-		 * wasting cycles loading values that might soon be overridden from
-		 * the config file, and to avoid trying to read the timezone files
-		 * during InitializeGUCOptions().  The latter doesn't work in an
-		 * EXEC_BACKEND subprocess because my_exec_path hasn't been set yet
-		 * and so we can't locate PGSHAREDIR.
-		 */
-		Assert(source == PGC_S_DEFAULT);
-		return true;
-	}
-
 	/*
 	 * Initialize the "extra" struct that will be passed to assign_timezone.
 	 * We don't want to change any of the three global variables except as
@@ -374,7 +357,7 @@ check_timezone(char **newval, void **extra, GucSource source)
 				return false;
 			}
 
-			if (!tz_acceptable(new_tz))
+			if (!pg_tz_acceptable(new_tz))
 			{
 				GUC_check_errmsg("time zone \"%s\" appears to use leap seconds",
 								 *newval);
@@ -427,10 +410,6 @@ assign_timezone(const char *newval, void *extra)
 {
 	timezone_extra *myextra = (timezone_extra *) extra;
 
-	/* Do nothing for the boot_val default of NULL */
-	if (!myextra)
-		return;
-
 	session_timezone = myextra->session_timezone;
 	CTimeZone = myextra->CTimeZone;
 	HasCTZSet = myextra->HasCTZSet;
@@ -490,20 +469,8 @@ check_log_timezone(char **newval, void **extra, GucSource source)
 {
 	pg_tz	   *new_tz;
 
-	if (*newval == NULL)
-	{
-		/*
-		 * The boot_val given for log_timezone in guc.c is NULL.  When we see
-		 * this we just do nothing.  If this isn't overridden from the config
-		 * file then pg_timezone_initialize() will eventually select a default
-		 * value from the environment.
-		 */
-		Assert(source == PGC_S_DEFAULT);
-		return true;
-	}
-
 	/*
-	 * Otherwise assume it is a timezone name, and try to load it.
+	 * Assume it is a timezone name, and try to load it.
 	 */
 	new_tz = pg_tzset(*newval);
 
@@ -513,7 +480,7 @@ check_log_timezone(char **newval, void **extra, GucSource source)
 		return false;
 	}
 
-	if (!tz_acceptable(new_tz))
+	if (!pg_tz_acceptable(new_tz))
 	{
 		GUC_check_errmsg("time zone \"%s\" appears to use leap seconds",
 						 *newval);
@@ -538,10 +505,6 @@ check_log_timezone(char **newval, void **extra, GucSource source)
 void
 assign_log_timezone(const char *newval, void *extra)
 {
-	/* Do nothing for the boot_val default of NULL */
-	if (!extra)
-		return;
-
 	log_timezone = *((pg_tz **) extra);
 }
 
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index df4a2aa8853..94b57fa7bbd 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -795,21 +795,6 @@ PostmasterMain(int argc, char *argv[])
 	 */
 	CreateDataDirLockFile(true);
 
-	/*
-	 * If timezone is not set, determine what the OS uses.	(In theory this
-	 * should be done during GUC initialization, but because it can take as
-	 * much as several seconds, we delay it until after we've created the
-	 * postmaster.pid file.  This prevents problems with boot scripts that
-	 * expect the pidfile to appear quickly.  Also, we avoid problems with
-	 * trying to locate the timezone files too early in initialization.)
-	 */
-	pg_timezone_initialize();
-
-	/*
-	 * Likewise, init timezone_abbreviations if not already set.
-	 */
-	pg_timezone_abbrev_initialize();
-
 	/*
 	 * Initialize SSL library, if specified.
 	 */
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index b708328926a..072d50c3951 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -3537,10 +3537,6 @@ PostgresMain(int argc, char *argv[], const char *username)
 	{
 		if (!SelectConfigFiles(userDoption, progname))
 			proc_exit(1);
-		/* If timezone is not set, determine what the OS uses */
-		pg_timezone_initialize();
-		/* If timezone_abbreviations is not set, select default */
-		pg_timezone_abbrev_initialize();
 	}
 
 	/*
diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index 6e8e5aef4e0..f0b3b1feb06 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -1805,24 +1805,20 @@ setup_formatted_log_time(void)
 {
 	struct timeval tv;
 	pg_time_t	stamp_time;
-	pg_tz	   *tz;
 	char		msbuf[8];
 
 	gettimeofday(&tv, NULL);
 	stamp_time = (pg_time_t) tv.tv_sec;
 
 	/*
-	 * Normally we print log timestamps in log_timezone, but during startup we
-	 * could get here before that's set. If so, fall back to gmt_timezone
-	 * (which guc.c ensures is set up before Log_line_prefix can become
-	 * nonempty).
+	 * Note: we expect that guc.c will ensure that log_timezone is set up
+	 * (at least with a minimal GMT value) before Log_line_prefix can become
+	 * nonempty or CSV mode can be selected.
 	 */
-	tz = log_timezone ? log_timezone : gmt_timezone;
-
 	pg_strftime(formatted_log_time, FORMATTED_TS_LEN,
 	/* leave room for milliseconds... */
 				"%Y-%m-%d %H:%M:%S     %Z",
-				pg_localtime(&stamp_time, tz));
+				pg_localtime(&stamp_time, log_timezone));
 
 	/* 'paste' milliseconds into place... */
 	sprintf(msbuf, ".%03d", (int) (tv.tv_usec / 1000));
@@ -1836,19 +1832,15 @@ static void
 setup_formatted_start_time(void)
 {
 	pg_time_t	stamp_time = (pg_time_t) MyStartTime;
-	pg_tz	   *tz;
 
 	/*
-	 * Normally we print log timestamps in log_timezone, but during startup we
-	 * could get here before that's set. If so, fall back to gmt_timezone
-	 * (which guc.c ensures is set up before Log_line_prefix can become
-	 * nonempty).
+	 * Note: we expect that guc.c will ensure that log_timezone is set up
+	 * (at least with a minimal GMT value) before Log_line_prefix can become
+	 * nonempty or CSV mode can be selected.
 	 */
-	tz = log_timezone ? log_timezone : gmt_timezone;
-
 	pg_strftime(formatted_start_time, FORMATTED_TS_LEN,
 				"%Y-%m-%d %H:%M:%S %Z",
-				pg_localtime(&stamp_time, tz));
+				pg_localtime(&stamp_time, log_timezone));
 }
 
 /*
@@ -1947,14 +1939,11 @@ log_line_prefix(StringInfo buf, ErrorData *edata)
 			case 't':
 				{
 					pg_time_t	stamp_time = (pg_time_t) time(NULL);
-					pg_tz	   *tz;
 					char		strfbuf[128];
 
-					tz = log_timezone ? log_timezone : gmt_timezone;
-
 					pg_strftime(strfbuf, sizeof(strfbuf),
 								"%Y-%m-%d %H:%M:%S %Z",
-								pg_localtime(&stamp_time, tz));
+								pg_localtime(&stamp_time, log_timezone));
 					appendStringInfoString(buf, strfbuf);
 				}
 				break;
diff --git a/src/backend/utils/misc/guc-file.l b/src/backend/utils/misc/guc-file.l
index 70abf40a28e..809307da8d3 100644
--- a/src/backend/utils/misc/guc-file.l
+++ b/src/backend/utils/misc/guc-file.l
@@ -292,7 +292,6 @@ ProcessConfigFile(GucContext context)
 	if (context == PGC_SIGHUP)
 	{
 		InitializeGUCOptionsFromEnvironment();
-		pg_timezone_initialize();
 		pg_timezone_abbrev_initialize();
 		/* this selects SQL_ASCII in processes not connected to a database */
 		SetConfigOption("client_encoding", GetDatabaseEncodingName(),
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 6670997acde..a71729c2e70 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -187,6 +187,7 @@ static bool check_log_stats(bool *newval, void **extra, GucSource source);
 static bool check_canonical_path(char **newval, void **extra, GucSource source);
 static bool check_timezone_abbreviations(char **newval, void **extra, GucSource source);
 static void assign_timezone_abbreviations(const char *newval, void *extra);
+static void pg_timezone_abbrev_initialize(void);
 static const char *show_archive_command(void);
 static void assign_tcp_keepalives_idle(int newval, void *extra);
 static void assign_tcp_keepalives_interval(int newval, void *extra);
@@ -2547,7 +2548,7 @@ static struct config_string ConfigureNamesString[] =
 			NULL
 		},
 		&log_timezone_string,
-		NULL,
+		"GMT",
 		check_log_timezone, assign_log_timezone, show_log_timezone
 	},
 
@@ -2827,7 +2828,7 @@ static struct config_string ConfigureNamesString[] =
 			GUC_REPORT
 		},
 		&timezone_string,
-		NULL,
+		"GMT",
 		check_timezone, assign_timezone, show_timezone
 	},
 	{
@@ -3817,7 +3818,7 @@ InitializeGUCOptions(void)
 	 * Before log_line_prefix could possibly receive a nonempty setting, make
 	 * sure that timezone processing is minimally alive (see elog.c).
 	 */
-	pg_timezone_pre_initialize();
+	pg_timezone_initialize();
 
 	/*
 	 * Build sorted array of all GUC variables.
@@ -4114,6 +4115,15 @@ SelectConfigFiles(const char *userDoption, const char *progname)
 	 */
 	SetConfigOption("data_directory", DataDir, PGC_POSTMASTER, PGC_S_OVERRIDE);
 
+	/*
+	 * If timezone_abbreviations wasn't set in the configuration file, install
+	 * the default value.  We do it this way because we can't safely install
+	 * a "real" value until my_exec_path is set, which may not have happened
+	 * when InitializeGUCOptions runs, so the bootstrap default value cannot
+	 * be the real desired default.
+	 */
+	pg_timezone_abbrev_initialize();
+
 	/*
 	 * Figure out where pg_hba.conf is, and make sure the path is absolute.
 	 */
@@ -8444,8 +8454,11 @@ assign_timezone_abbreviations(const char *newval, void *extra)
  * This is called after initial loading of postgresql.conf.  If no
  * timezone_abbreviations setting was found therein, select default.
  * If a non-default value is already installed, nothing will happen.
+ *
+ * This can also be called from ProcessConfigFile to establish the default
+ * value after a postgresql.conf entry for it is removed.
  */
-void
+static void
 pg_timezone_abbrev_initialize(void)
 {
 	SetConfigOption("timezone_abbreviations", "Default",
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index e713defea2c..a18f14ae253 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -406,7 +406,7 @@
 #log_temp_files = -1			# log temporary files equal or larger
 					# than the specified size in kilobytes;
 					# -1 disables, 0 logs all temp files
-#log_timezone = '(defaults to server environment setting)'
+#log_timezone = 'GMT'
 
 
 #------------------------------------------------------------------------------
@@ -486,7 +486,7 @@
 
 #datestyle = 'iso, mdy'
 #intervalstyle = 'postgres'
-#timezone = '(defaults to server environment setting)'
+#timezone = 'GMT'
 #timezone_abbreviations = 'Default'     # Select the set of available time zone
 					# abbreviations.  Currently, there are
 					#   Default
diff --git a/src/bin/initdb/.gitignore b/src/bin/initdb/.gitignore
index 843eaf0c1e2..c0ed2e8d169 100644
--- a/src/bin/initdb/.gitignore
+++ b/src/bin/initdb/.gitignore
@@ -1,4 +1,5 @@
 /encnames.c
 /pqsignal.c
+/localtime.c
 
 /initdb
diff --git a/src/bin/initdb/Makefile b/src/bin/initdb/Makefile
index 7dd66838133..8bd1e6d3a9e 100644
--- a/src/bin/initdb/Makefile
+++ b/src/bin/initdb/Makefile
@@ -16,9 +16,9 @@ subdir = src/bin/initdb
 top_builddir = ../../..
 include $(top_builddir)/src/Makefile.global
 
-override CPPFLAGS := -DFRONTEND -I$(libpq_srcdir) $(CPPFLAGS)
+override CPPFLAGS := -DFRONTEND -I$(libpq_srcdir) -I$(top_srcdir)/src/timezone $(CPPFLAGS)
 
-OBJS=	initdb.o encnames.o pqsignal.o $(WIN32RES)
+OBJS=	initdb.o findtimezone.o localtime.o encnames.o pqsignal.o $(WIN32RES)
 
 all: initdb
 
@@ -35,6 +35,11 @@ encnames.c: % : $(top_srcdir)/src/backend/utils/mb/%
 pqsignal.c: % : $(top_srcdir)/src/interfaces/libpq/%
 	rm -f $@ && $(LN_S) $< .
 
+# Likewise, pull in localtime.c from src/timezones
+
+localtime.c: % : $(top_srcdir)/src/timezone/%
+	rm -f $@ && $(LN_S) $< .
+
 install: all installdirs
 	$(INSTALL_PROGRAM) initdb$(X) '$(DESTDIR)$(bindir)/initdb$(X)'
 
@@ -45,7 +50,7 @@ uninstall:
 	rm -f '$(DESTDIR)$(bindir)/initdb$(X)'
 
 clean distclean maintainer-clean:
-	rm -f initdb$(X) $(OBJS) encnames.c pqsignal.c
+	rm -f initdb$(X) $(OBJS) encnames.c pqsignal.c localtime.c
 
 
 # ensure that changes in datadir propagate into object file
diff --git a/src/bin/initdb/findtimezone.c b/src/bin/initdb/findtimezone.c
new file mode 100644
index 00000000000..6d45674b5b8
--- /dev/null
+++ b/src/bin/initdb/findtimezone.c
@@ -0,0 +1,1224 @@
+/*-------------------------------------------------------------------------
+ *
+ * findtimezone.c
+ *	  Functions for determining the default timezone to use.
+ *
+ * Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/bin/initdb/findtimezone.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres_fe.h"
+
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <time.h>
+
+#include "pgtz.h"
+
+/* Ideally this would be in a .h file, but it hardly seems worth the trouble */
+extern const char *select_default_timezone(const char *share_path);
+
+
+#ifndef SYSTEMTZDIR
+static char tzdirpath[MAXPGPATH];
+#endif
+
+
+/*
+ * Return full pathname of timezone data directory
+ *
+ * In this file, tzdirpath is assumed to be set up by select_default_timezone.
+ */
+static const char *
+pg_TZDIR(void)
+{
+#ifndef SYSTEMTZDIR
+	/* normal case: timezone stuff is under our share dir */
+	return tzdirpath;
+#else
+	/* we're configured to use system's timezone database */
+	return SYSTEMTZDIR;
+#endif
+}
+
+
+/*
+ * Given a timezone name, open() the timezone data file.  Return the
+ * file descriptor if successful, -1 if not.
+ *
+ * This is simpler than the backend function of the same name because
+ * we assume that the input string has the correct case already, so there
+ * is no need for case-folding.  (This is obviously true if we got the file
+ * name from the filesystem to start with.  The only other place it can come
+ * from is the environment variable TZ, and there seems no need to allow
+ * case variation in that; other programs aren't likely to.)
+ *
+ * If "canonname" is not NULL, then on success the canonical spelling of the
+ * given name is stored there (the buffer must be > TZ_STRLEN_MAX bytes!).
+ * This is redundant but kept for compatibility with the backend code.
+ */
+int
+pg_open_tzfile(const char *name, char *canonname)
+{
+	char		fullname[MAXPGPATH];
+
+	if (canonname)
+		strlcpy(canonname, name, TZ_STRLEN_MAX + 1);
+
+	strcpy(fullname, pg_TZDIR());
+	if (strlen(fullname) + 1 + strlen(name) >= MAXPGPATH)
+		return -1;				/* not gonna fit */
+	strcat(fullname, "/");
+	strcat(fullname, name);
+
+	return open(fullname, O_RDONLY | PG_BINARY, 0);
+}
+
+
+
+/*
+ * Load a timezone definition.
+ * Does not verify that the timezone is acceptable!
+ *
+ * This corresponds to the backend's pg_tzset(), except that we only support
+ * one loaded timezone at a time.
+ */
+static pg_tz *
+pg_load_tz(const char *name)
+{
+	static pg_tz tz;
+
+	if (strlen(name) > TZ_STRLEN_MAX)
+		return NULL;			/* not going to fit */
+
+	/*
+	 * "GMT" is always sent to tzparse(); see comments for pg_tzset().
+	 */
+	if (strcmp(name, "GMT") == 0)
+	{
+		if (tzparse(name, &tz.state, TRUE) != 0)
+		{
+			/* This really, really should not happen ... */
+			return NULL;
+		}
+	}
+	else if (tzload(name, NULL, &tz.state, TRUE) != 0)
+	{
+		if (name[0] == ':' || tzparse(name, &tz.state, FALSE) != 0)
+		{
+			return NULL;		/* unknown timezone */
+		}
+	}
+
+	strcpy(tz.TZname, name);
+
+	return &tz;
+}
+
+
+/*
+ * The following block of code attempts to determine which timezone in our
+ * timezone database is the best match for the active system timezone.
+ *
+ * On most systems, we rely on trying to match the observable behavior of
+ * the C library's localtime() function.  The database zone that matches
+ * furthest into the past is the one to use.  Often there will be several
+ * zones with identical rankings (since the Olson database assigns multiple
+ * names to many zones).  We break ties arbitrarily by preferring shorter,
+ * then alphabetically earlier zone names.
+ *
+ * Win32's native knowledge about timezones appears to be too incomplete
+ * and too different from the Olson database for the above matching strategy
+ * to be of any use. But there is just a limited number of timezones
+ * available, so we can rely on a handmade mapping table instead.
+ */
+
+#ifndef WIN32
+
+#define T_DAY	((time_t) (60*60*24))
+#define T_WEEK	((time_t) (60*60*24*7))
+#define T_MONTH ((time_t) (60*60*24*31))
+
+#define MAX_TEST_TIMES (52*100) /* 100 years */
+
+struct tztry
+{
+	int			n_test_times;
+	time_t		test_times[MAX_TEST_TIMES];
+};
+
+static void scan_available_timezones(char *tzdir, char *tzdirsub,
+						 struct tztry * tt,
+						 int *bestscore, char *bestzonename);
+
+
+/*
+ * Get GMT offset from a system struct tm
+ */
+static int
+get_timezone_offset(struct tm * tm)
+{
+#if defined(HAVE_STRUCT_TM_TM_ZONE)
+	return tm->tm_gmtoff;
+#elif defined(HAVE_INT_TIMEZONE)
+	return -TIMEZONE_GLOBAL;
+#else
+#error No way to determine TZ? Can this happen?
+#endif
+}
+
+/*
+ * Convenience subroutine to convert y/m/d to time_t (NOT pg_time_t)
+ */
+static time_t
+build_time_t(int year, int month, int day)
+{
+	struct tm	tm;
+
+	memset(&tm, 0, sizeof(tm));
+	tm.tm_mday = day;
+	tm.tm_mon = month - 1;
+	tm.tm_year = year - 1900;
+
+	return mktime(&tm);
+}
+
+/*
+ * Does a system tm value match one we computed ourselves?
+ */
+static bool
+compare_tm(struct tm * s, struct pg_tm * p)
+{
+	if (s->tm_sec != p->tm_sec ||
+		s->tm_min != p->tm_min ||
+		s->tm_hour != p->tm_hour ||
+		s->tm_mday != p->tm_mday ||
+		s->tm_mon != p->tm_mon ||
+		s->tm_year != p->tm_year ||
+		s->tm_wday != p->tm_wday ||
+		s->tm_yday != p->tm_yday ||
+		s->tm_isdst != p->tm_isdst)
+		return false;
+	return true;
+}
+
+/*
+ * See how well a specific timezone setting matches the system behavior
+ *
+ * We score a timezone setting according to the number of test times it
+ * matches.  (The test times are ordered later-to-earlier, but this routine
+ * doesn't actually know that; it just scans until the first non-match.)
+ *
+ * We return -1 for a completely unusable setting; this is worse than the
+ * score of zero for a setting that works but matches not even the first
+ * test time.
+ */
+static int
+score_timezone(const char *tzname, struct tztry * tt)
+{
+	int			i;
+	pg_time_t	pgtt;
+	struct tm  *systm;
+	struct pg_tm *pgtm;
+	char		cbuf[TZ_STRLEN_MAX + 1];
+	pg_tz	   *tz;
+
+	/* Load timezone definition */
+	tz = pg_load_tz(tzname);
+	if (!tz)
+		return -1;				/* unrecognized zone name */
+
+	/* Reject if leap seconds involved */
+	if (!pg_tz_acceptable(tz))
+	{
+#ifdef DEBUG_IDENTIFY_TIMEZONE
+		fprintf(stderr, "Reject TZ \"%s\": uses leap seconds\n", tzname);
+#endif
+		return -1;
+	}
+
+	/* Check for match at all the test times */
+	for (i = 0; i < tt->n_test_times; i++)
+	{
+		pgtt = (pg_time_t) (tt->test_times[i]);
+		pgtm = pg_localtime(&pgtt, tz);
+		if (!pgtm)
+			return -1;			/* probably shouldn't happen */
+		systm = localtime(&(tt->test_times[i]));
+		if (!systm)
+		{
+#ifdef DEBUG_IDENTIFY_TIMEZONE
+			fprintf(stderr, "TZ \"%s\" scores %d: at %ld %04d-%02d-%02d %02d:%02d:%02d %s, system had no data\n",
+					tzname, i, (long) pgtt,
+					pgtm->tm_year + 1900, pgtm->tm_mon + 1, pgtm->tm_mday,
+					pgtm->tm_hour, pgtm->tm_min, pgtm->tm_sec,
+					pgtm->tm_isdst ? "dst" : "std");
+#endif
+			return i;
+		}
+		if (!compare_tm(systm, pgtm))
+		{
+#ifdef DEBUG_IDENTIFY_TIMEZONE
+			fprintf(stderr, "TZ \"%s\" scores %d: at %ld %04d-%02d-%02d %02d:%02d:%02d %s versus %04d-%02d-%02d %02d:%02d:%02d %s\n",
+					tzname, i, (long) pgtt,
+					pgtm->tm_year + 1900, pgtm->tm_mon + 1, pgtm->tm_mday,
+					pgtm->tm_hour, pgtm->tm_min, pgtm->tm_sec,
+					pgtm->tm_isdst ? "dst" : "std",
+					systm->tm_year + 1900, systm->tm_mon + 1, systm->tm_mday,
+					systm->tm_hour, systm->tm_min, systm->tm_sec,
+					systm->tm_isdst ? "dst" : "std");
+#endif
+			return i;
+		}
+		if (systm->tm_isdst >= 0)
+		{
+			/* Check match of zone names, too */
+			if (pgtm->tm_zone == NULL)
+				return -1;		/* probably shouldn't happen */
+			memset(cbuf, 0, sizeof(cbuf));
+			strftime(cbuf, sizeof(cbuf) - 1, "%Z", systm);		/* zone abbr */
+			if (strcmp(cbuf, pgtm->tm_zone) != 0)
+			{
+#ifdef DEBUG_IDENTIFY_TIMEZONE
+				fprintf(stderr, "TZ \"%s\" scores %d: at %ld \"%s\" versus \"%s\"\n",
+						tzname, i, (long) pgtt,
+						pgtm->tm_zone, cbuf);
+#endif
+				return i;
+			}
+		}
+	}
+
+#ifdef DEBUG_IDENTIFY_TIMEZONE
+	fprintf(stderr, "TZ \"%s\" gets max score %d\n", tzname, i);
+#endif
+
+	return i;
+}
+
+
+/*
+ * Try to identify a timezone name (in our terminology) that best matches the
+ * observed behavior of the system timezone library.  We cannot assume that
+ * the system TZ environment setting (if indeed there is one) matches our
+ * terminology, so we ignore it and just look at what localtime() returns.
+ */
+static const char *
+identify_system_timezone(void)
+{
+	static char resultbuf[TZ_STRLEN_MAX + 1];
+	time_t		tnow;
+	time_t		t;
+	struct tztry tt;
+	struct tm  *tm;
+	int			thisyear;
+	int			bestscore;
+	char		tmptzdir[MAXPGPATH];
+	int			std_ofs;
+	char		std_zone_name[TZ_STRLEN_MAX + 1],
+				dst_zone_name[TZ_STRLEN_MAX + 1];
+	char		cbuf[TZ_STRLEN_MAX + 1];
+
+	/* Initialize OS timezone library */
+	tzset();
+
+	/*
+	 * Set up the list of dates to be probed to see how well our timezone
+	 * matches the system zone.  We first probe January and July of the
+	 * current year; this serves to quickly eliminate the vast majority of the
+	 * TZ database entries.  If those dates match, we probe every week for 100
+	 * years backwards from the current July.  (Weekly resolution is good
+	 * enough to identify DST transition rules, since everybody switches on
+	 * Sundays.)  This is sufficient to cover most of the Unix time_t range,
+	 * and we don't want to look further than that since many systems won't
+	 * have sane TZ behavior further back anyway.  The further back the zone
+	 * matches, the better we score it.  This may seem like a rather random
+	 * way of doing things, but experience has shown that system-supplied
+	 * timezone definitions are likely to have DST behavior that is right for
+	 * the recent past and not so accurate further back. Scoring in this way
+	 * allows us to recognize zones that have some commonality with the Olson
+	 * database, without insisting on exact match. (Note: we probe Thursdays,
+	 * not Sundays, to avoid triggering DST-transition bugs in localtime
+	 * itself.)
+	 */
+	tnow = time(NULL);
+	tm = localtime(&tnow);
+	if (!tm)
+		return NULL;			/* give up if localtime is broken... */
+	thisyear = tm->tm_year + 1900;
+
+	t = build_time_t(thisyear, 1, 15);
+
+	/*
+	 * Round back to GMT midnight Thursday.  This depends on the knowledge
+	 * that the time_t origin is Thu Jan 01 1970.  (With a different origin
+	 * we'd be probing some other day of the week, but it wouldn't matter
+	 * anyway unless localtime() had DST-transition bugs.)
+	 */
+	t -= (t % T_WEEK);
+
+	tt.n_test_times = 0;
+	tt.test_times[tt.n_test_times++] = t;
+
+	t = build_time_t(thisyear, 7, 15);
+	t -= (t % T_WEEK);
+
+	tt.test_times[tt.n_test_times++] = t;
+
+	while (tt.n_test_times < MAX_TEST_TIMES)
+	{
+		t -= T_WEEK;
+		tt.test_times[tt.n_test_times++] = t;
+	}
+
+	/* Search for the best-matching timezone file */
+	strcpy(tmptzdir, pg_TZDIR());
+	bestscore = -1;
+	resultbuf[0] = '\0';
+	scan_available_timezones(tmptzdir, tmptzdir + strlen(tmptzdir) + 1,
+							 &tt,
+							 &bestscore, resultbuf);
+	if (bestscore > 0)
+	{
+		/* Ignore Olson's rather silly "Factory" zone; use GMT instead */
+		if (strcmp(resultbuf, "Factory") == 0)
+			return NULL;
+		return resultbuf;
+	}
+
+	/*
+	 * Couldn't find a match in the database, so next we try constructed zone
+	 * names (like "PST8PDT").
+	 *
+	 * First we need to determine the names of the local standard and daylight
+	 * zones.  The idea here is to scan forward from today until we have seen
+	 * both zones, if both are in use.
+	 */
+	memset(std_zone_name, 0, sizeof(std_zone_name));
+	memset(dst_zone_name, 0, sizeof(dst_zone_name));
+	std_ofs = 0;
+
+	tnow = time(NULL);
+
+	/*
+	 * Round back to a GMT midnight so results don't depend on local time of
+	 * day
+	 */
+	tnow -= (tnow % T_DAY);
+
+	/*
+	 * We have to look a little further ahead than one year, in case today is
+	 * just past a DST boundary that falls earlier in the year than the next
+	 * similar boundary.  Arbitrarily scan up to 14 months.
+	 */
+	for (t = tnow; t <= tnow + T_MONTH * 14; t += T_MONTH)
+	{
+		tm = localtime(&t);
+		if (!tm)
+			continue;
+		if (tm->tm_isdst < 0)
+			continue;
+		if (tm->tm_isdst == 0 && std_zone_name[0] == '\0')
+		{
+			/* found STD zone */
+			memset(cbuf, 0, sizeof(cbuf));
+			strftime(cbuf, sizeof(cbuf) - 1, "%Z", tm); /* zone abbr */
+			strcpy(std_zone_name, cbuf);
+			std_ofs = get_timezone_offset(tm);
+		}
+		if (tm->tm_isdst > 0 && dst_zone_name[0] == '\0')
+		{
+			/* found DST zone */
+			memset(cbuf, 0, sizeof(cbuf));
+			strftime(cbuf, sizeof(cbuf) - 1, "%Z", tm); /* zone abbr */
+			strcpy(dst_zone_name, cbuf);
+		}
+		/* Done if found both */
+		if (std_zone_name[0] && dst_zone_name[0])
+			break;
+	}
+
+	/* We should have found a STD zone name by now... */
+	if (std_zone_name[0] == '\0')
+	{
+#ifdef DEBUG_IDENTIFY_TIMEZONE
+		fprintf(stderr, "could not determine system time zone\n");
+#endif
+		return NULL;			/* go to GMT */
+	}
+
+	/* If we found DST then try STD<ofs>DST */
+	if (dst_zone_name[0] != '\0')
+	{
+		snprintf(resultbuf, sizeof(resultbuf), "%s%d%s",
+				 std_zone_name, -std_ofs / 3600, dst_zone_name);
+		if (score_timezone(resultbuf, &tt) > 0)
+			return resultbuf;
+	}
+
+	/* Try just the STD timezone (works for GMT at least) */
+	strcpy(resultbuf, std_zone_name);
+	if (score_timezone(resultbuf, &tt) > 0)
+		return resultbuf;
+
+	/* Try STD<ofs> */
+	snprintf(resultbuf, sizeof(resultbuf), "%s%d",
+			 std_zone_name, -std_ofs / 3600);
+	if (score_timezone(resultbuf, &tt) > 0)
+		return resultbuf;
+
+	/*
+	 * Did not find the timezone.  Fallback to use a GMT zone.	Note that the
+	 * Olson timezone database names the GMT-offset zones in POSIX style: plus
+	 * is west of Greenwich.  It's unfortunate that this is opposite of SQL
+	 * conventions.  Should we therefore change the names? Probably not...
+	 */
+	snprintf(resultbuf, sizeof(resultbuf), "Etc/GMT%s%d",
+			 (-std_ofs > 0) ? "+" : "", -std_ofs / 3600);
+
+#ifdef DEBUG_IDENTIFY_TIMEZONE
+	fprintf(stderr, "could not recognize system time zone, using \"%s\"\n",
+			resultbuf);
+#endif
+	return resultbuf;
+}
+
+/*
+ * Recursively scan the timezone database looking for the best match to
+ * the system timezone behavior.
+ *
+ * tzdir points to a buffer of size MAXPGPATH.	On entry, it holds the
+ * pathname of a directory containing TZ files.  We internally modify it
+ * to hold pathnames of sub-directories and files, but must restore it
+ * to its original contents before exit.
+ *
+ * tzdirsub points to the part of tzdir that represents the subfile name
+ * (ie, tzdir + the original directory name length, plus one for the
+ * first added '/').
+ *
+ * tt tells about the system timezone behavior we need to match.
+ *
+ * *bestscore and *bestzonename on entry hold the best score found so far
+ * and the name of the best zone.  We overwrite them if we find a better
+ * score.  bestzonename must be a buffer of length TZ_STRLEN_MAX + 1.
+ */
+static void
+scan_available_timezones(char *tzdir, char *tzdirsub, struct tztry * tt,
+						 int *bestscore, char *bestzonename)
+{
+	int			tzdir_orig_len = strlen(tzdir);
+	char	  **names;
+	char	  **namep;
+
+	names = pgfnames(tzdir);
+	if (!names)
+		return;
+
+	for (namep = names; *namep; namep++)
+	{
+		char	   *name = *namep;
+		struct stat statbuf;
+
+		/* Ignore . and .., plus any other "hidden" files */
+		if (name[0] == '.')
+			continue;
+
+		snprintf(tzdir + tzdir_orig_len, MAXPGPATH - tzdir_orig_len,
+				 "/%s", name);
+
+		if (stat(tzdir, &statbuf) != 0)
+		{
+#ifdef DEBUG_IDENTIFY_TIMEZONE
+			fprintf(stderr, "could not stat \"%s\": %s\n",
+					tzdir, strerror(errno));
+#endif
+			tzdir[tzdir_orig_len] = '\0';
+			continue;
+		}
+
+		if (S_ISDIR(statbuf.st_mode))
+		{
+			/* Recurse into subdirectory */
+			scan_available_timezones(tzdir, tzdirsub, tt,
+									 bestscore, bestzonename);
+		}
+		else
+		{
+			/* Load and test this file */
+			int			score = score_timezone(tzdirsub, tt);
+
+			if (score > *bestscore)
+			{
+				*bestscore = score;
+				strlcpy(bestzonename, tzdirsub, TZ_STRLEN_MAX + 1);
+			}
+			else if (score == *bestscore)
+			{
+				/* Consider how to break a tie */
+				if (strlen(tzdirsub) < strlen(bestzonename) ||
+					(strlen(tzdirsub) == strlen(bestzonename) &&
+					 strcmp(tzdirsub, bestzonename) < 0))
+					strlcpy(bestzonename, tzdirsub, TZ_STRLEN_MAX + 1);
+			}
+		}
+
+		/* Restore tzdir */
+		tzdir[tzdir_orig_len] = '\0';
+	}
+
+	pgfnames_cleanup(names);
+}
+
+#else							/* WIN32 */
+
+static const struct
+{
+	const char *stdname;		/* Windows name of standard timezone */
+	const char *dstname;		/* Windows name of daylight timezone */
+	const char *pgtzname;		/* Name of pgsql timezone to map to */
+}	win32_tzmap[] =
+
+{
+	/*
+	 * This list was built from the contents of the registry at
+	 * HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time
+	 * Zones on Windows 2003 R2.
+	 *
+	 * The zones have been matched to Olson timezones by looking at the cities
+	 * listed in the win32 display name (in the comment here) in most cases.
+	 */
+	{
+		"Afghanistan Standard Time", "Afghanistan Daylight Time",
+		"Asia/Kabul"
+	},							/* (GMT+04:30) Kabul */
+	{
+		"Alaskan Standard Time", "Alaskan Daylight Time",
+		"US/Alaska"
+	},							/* (GMT-09:00) Alaska */
+	{
+		"Arab Standard Time", "Arab Daylight Time",
+		"Asia/Kuwait"
+	},							/* (GMT+03:00) Kuwait, Riyadh */
+	{
+		"Arabian Standard Time", "Arabian Daylight Time",
+		"Asia/Muscat"
+	},							/* (GMT+04:00) Abu Dhabi, Muscat */
+	{
+		"Arabic Standard Time", "Arabic Daylight Time",
+		"Asia/Baghdad"
+	},							/* (GMT+03:00) Baghdad */
+	{
+		"Argentina Standard Time", "Argentina Daylight Time",
+		"America/Buenos_Aires"
+	},							/* (GMT-03:00) Buenos Aires */
+	{
+		"Armenian Standard Time", "Armenian Daylight Time",
+		"Asia/Yerevan"
+	},							/* (GMT+04:00) Yerevan */
+	{
+		"Atlantic Standard Time", "Atlantic Daylight Time",
+		"Canada/Atlantic"
+	},							/* (GMT-04:00) Atlantic Time (Canada) */
+	{
+		"AUS Central Standard Time", "AUS Central Daylight Time",
+		"Australia/Darwin"
+	},							/* (GMT+09:30) Darwin */
+	{
+		"AUS Eastern Standard Time", "AUS Eastern Daylight Time",
+		"Australia/Canberra"
+	},							/* (GMT+10:00) Canberra, Melbourne, Sydney */
+	{
+		"Azerbaijan Standard Time", "Azerbaijan Daylight Time",
+		"Asia/Baku"
+	},							/* (GMT+04:00) Baku */
+	{
+		"Azores Standard Time", "Azores Daylight Time",
+		"Atlantic/Azores"
+	},							/* (GMT-01:00) Azores */
+	{
+		"Bangladesh Standard Time", "Bangladesh Daylight Time",
+		"Asia/Dhaka"
+	},							/* (GMT+06:00) Dhaka */
+	{
+		"Canada Central Standard Time", "Canada Central Daylight Time",
+		"Canada/Saskatchewan"
+	},							/* (GMT-06:00) Saskatchewan */
+	{
+		"Cape Verde Standard Time", "Cape Verde Daylight Time",
+		"Atlantic/Cape_Verde"
+	},							/* (GMT-01:00) Cape Verde Is. */
+	{
+		"Caucasus Standard Time", "Caucasus Daylight Time",
+		"Asia/Baku"
+	},							/* (GMT+04:00) Baku, Tbilisi, Yerevan */
+	{
+		"Cen. Australia Standard Time", "Cen. Australia Daylight Time",
+		"Australia/Adelaide"
+	},							/* (GMT+09:30) Adelaide */
+	{
+		"Central America Standard Time", "Central America Daylight Time",
+		"CST6CDT"
+	},							/* (GMT-06:00) Central America */
+	{
+		"Central Asia Standard Time", "Central Asia Daylight Time",
+		"Asia/Dhaka"
+	},							/* (GMT+06:00) Astana, Dhaka */
+	{
+		"Central Brazilian Standard Time", "Central Brazilian Daylight Time",
+		"America/Cuiaba"
+	},							/* (GMT-04:00) Cuiaba */
+	{
+		"Central Europe Standard Time", "Central Europe Daylight Time",
+		"Europe/Belgrade"
+	},							/* (GMT+01:00) Belgrade, Bratislava, Budapest,
+								 * Ljubljana, Prague */
+	{
+		"Central European Standard Time", "Central European Daylight Time",
+		"Europe/Sarajevo"
+	},							/* (GMT+01:00) Sarajevo, Skopje, Warsaw,
+								 * Zagreb */
+	{
+		"Central Pacific Standard Time", "Central Pacific Daylight Time",
+		"Pacific/Noumea"
+	},							/* (GMT+11:00) Magadan, Solomon Is., New
+								 * Caledonia */
+	{
+		"Central Standard Time", "Central Daylight Time",
+		"US/Central"
+	},							/* (GMT-06:00) Central Time (US & Canada) */
+	{
+		"Central Standard Time (Mexico)", "Central Daylight Time (Mexico)",
+		"America/Mexico_City"
+	},							/* (GMT-06:00) Guadalajara, Mexico City,
+								 * Monterrey - New */
+	{
+		"China Standard Time", "China Daylight Time",
+		"Asia/Hong_Kong"
+	},							/* (GMT+08:00) Beijing, Chongqing, Hong Kong,
+								 * Urumqi */
+	{
+		"Dateline Standard Time", "Dateline Daylight Time",
+		"Etc/GMT+12"
+	},							/* (GMT-12:00) International Date Line West */
+	{
+		"E. Africa Standard Time", "E. Africa Daylight Time",
+		"Africa/Nairobi"
+	},							/* (GMT+03:00) Nairobi */
+	{
+		"E. Australia Standard Time", "E. Australia Daylight Time",
+		"Australia/Brisbane"
+	},							/* (GMT+10:00) Brisbane */
+	{
+		"E. Europe Standard Time", "E. Europe Daylight Time",
+		"Europe/Bucharest"
+	},							/* (GMT+02:00) Bucharest */
+	{
+		"E. South America Standard Time", "E. South America Daylight Time",
+		"America/Araguaina"
+	},							/* (GMT-03:00) Brasilia */
+	{
+		"Eastern Standard Time", "Eastern Daylight Time",
+		"US/Eastern"
+	},							/* (GMT-05:00) Eastern Time (US & Canada) */
+	{
+		"Egypt Standard Time", "Egypt Daylight Time",
+		"Africa/Cairo"
+	},							/* (GMT+02:00) Cairo */
+	{
+		"Ekaterinburg Standard Time", "Ekaterinburg Daylight Time",
+		"Asia/Yekaterinburg"
+	},							/* (GMT+05:00) Ekaterinburg */
+	{
+		"Fiji Standard Time", "Fiji Daylight Time",
+		"Pacific/Fiji"
+	},							/* (GMT+12:00) Fiji, Kamchatka, Marshall Is. */
+	{
+		"FLE Standard Time", "FLE Daylight Time",
+		"Europe/Helsinki"
+	},							/* (GMT+02:00) Helsinki, Kyiv, Riga, Sofia,
+								 * Tallinn, Vilnius */
+	{
+		"Georgian Standard Time", "Georgian Daylight Time",
+		"Asia/Tbilisi"
+	},							/* (GMT+03:00) Tbilisi */
+	{
+		"GMT Standard Time", "GMT Daylight Time",
+		"Europe/London"
+	},							/* (GMT) Greenwich Mean Time : Dublin,
+								 * Edinburgh, Lisbon, London */
+	{
+		"Greenland Standard Time", "Greenland Daylight Time",
+		"America/Godthab"
+	},							/* (GMT-03:00) Greenland */
+	{
+		"Greenwich Standard Time", "Greenwich Daylight Time",
+		"Africa/Casablanca"
+	},							/* (GMT) Casablanca, Monrovia */
+	{
+		"GTB Standard Time", "GTB Daylight Time",
+		"Europe/Athens"
+	},							/* (GMT+02:00) Athens, Istanbul, Minsk */
+	{
+		"Hawaiian Standard Time", "Hawaiian Daylight Time",
+		"US/Hawaii"
+	},							/* (GMT-10:00) Hawaii */
+	{
+		"India Standard Time", "India Daylight Time",
+		"Asia/Calcutta"
+	},							/* (GMT+05:30) Chennai, Kolkata, Mumbai, New
+								 * Delhi */
+	{
+		"Iran Standard Time", "Iran Daylight Time",
+		"Asia/Tehran"
+	},							/* (GMT+03:30) Tehran */
+	{
+		"Jerusalem Standard Time", "Jerusalem Daylight Time",
+		"Asia/Jerusalem"
+	},							/* (GMT+02:00) Jerusalem */
+	{
+		"Jordan Standard Time", "Jordan Daylight Time",
+		"Asia/Amman"
+	},							/* (GMT+02:00) Amman */
+	{
+		"Kamchatka Standard Time", "Kamchatka Daylight Time",
+		"Asia/Kamchatka"
+	},							/* (GMT+12:00) Petropavlovsk-Kamchatsky */
+	{
+		"Korea Standard Time", "Korea Daylight Time",
+		"Asia/Seoul"
+	},							/* (GMT+09:00) Seoul */
+	{
+		"Mauritius Standard Time", "Mauritius Daylight Time",
+		"Indian/Mauritius"
+	},							/* (GMT+04:00) Port Louis */
+	{
+		"Mexico Standard Time", "Mexico Daylight Time",
+		"America/Mexico_City"
+	},							/* (GMT-06:00) Guadalajara, Mexico City,
+								 * Monterrey */
+	{
+		"Mexico Standard Time 2", "Mexico Daylight Time 2",
+		"America/Chihuahua"
+	},							/* (GMT-07:00) Chihuahua, La Paz, Mazatlan */
+	{
+		"Mid-Atlantic Standard Time", "Mid-Atlantic Daylight Time",
+		"Atlantic/South_Georgia"
+	},							/* (GMT-02:00) Mid-Atlantic */
+	{
+		"Middle East Standard Time", "Middle East Daylight Time",
+		"Asia/Beirut"
+	},							/* (GMT+02:00) Beirut */
+	{
+		"Montevideo Standard Time", "Montevideo Daylight Time",
+		"America/Montevideo"
+	},							/* (GMT-03:00) Montevideo */
+	{
+		"Morocco Standard Time", "Morocco Daylight Time",
+		"Africa/Casablanca"
+	},							/* (GMT) Casablanca */
+	{
+		"Mountain Standard Time", "Mountain Daylight Time",
+		"US/Mountain"
+	},							/* (GMT-07:00) Mountain Time (US & Canada) */
+	{
+		"Mountain Standard Time (Mexico)", "Mountain Daylight Time (Mexico)",
+		"America/Chihuahua"
+	},							/* (GMT-07:00) Chihuahua, La Paz, Mazatlan -
+								 * New */
+	{
+		"Myanmar Standard Time", "Myanmar Daylight Time",
+		"Asia/Rangoon"
+	},							/* (GMT+06:30) Rangoon */
+	{
+		"N. Central Asia Standard Time", "N. Central Asia Daylight Time",
+		"Asia/Novosibirsk"
+	},							/* (GMT+06:00) Novosibirsk */
+	{
+		"Namibia Standard Time", "Namibia Daylight Time",
+		"Africa/Windhoek"
+	},							/* (GMT+02:00) Windhoek */
+	{
+		"Nepal Standard Time", "Nepal Daylight Time",
+		"Asia/Katmandu"
+	},							/* (GMT+05:45) Kathmandu */
+	{
+		"New Zealand Standard Time", "New Zealand Daylight Time",
+		"Pacific/Auckland"
+	},							/* (GMT+12:00) Auckland, Wellington */
+	{
+		"Newfoundland Standard Time", "Newfoundland Daylight Time",
+		"Canada/Newfoundland"
+	},							/* (GMT-03:30) Newfoundland */
+	{
+		"North Asia East Standard Time", "North Asia East Daylight Time",
+		"Asia/Irkutsk"
+	},							/* (GMT+08:00) Irkutsk, Ulaan Bataar */
+	{
+		"North Asia Standard Time", "North Asia Daylight Time",
+		"Asia/Krasnoyarsk"
+	},							/* (GMT+07:00) Krasnoyarsk */
+	{
+		"Pacific SA Standard Time", "Pacific SA Daylight Time",
+		"America/Santiago"
+	},							/* (GMT-04:00) Santiago */
+	{
+		"Pacific Standard Time", "Pacific Daylight Time",
+		"US/Pacific"
+	},							/* (GMT-08:00) Pacific Time (US & Canada);
+								 * Tijuana */
+	{
+		"Pacific Standard Time (Mexico)", "Pacific Daylight Time (Mexico)",
+		"America/Tijuana"
+	},							/* (GMT-08:00) Tijuana, Baja California */
+	{
+		"Pakistan Standard Time", "Pakistan Daylight Time",
+		"Asia/Karachi"
+	},							/* (GMT+05:00) Islamabad, Karachi */
+	{
+		"Paraguay Standard Time", "Paraguay Daylight Time",
+		"America/Asuncion"
+	},							/* (GMT-04:00) Asuncion */
+	{
+		"Romance Standard Time", "Romance Daylight Time",
+		"Europe/Brussels"
+	},							/* (GMT+01:00) Brussels, Copenhagen, Madrid,
+								 * Paris */
+	{
+		"Russian Standard Time", "Russian Daylight Time",
+		"Europe/Moscow"
+	},							/* (GMT+03:00) Moscow, St. Petersburg,
+								 * Volgograd */
+	{
+		"SA Eastern Standard Time", "SA Eastern Daylight Time",
+		"America/Buenos_Aires"
+	},							/* (GMT-03:00) Buenos Aires, Georgetown */
+	{
+		"SA Pacific Standard Time", "SA Pacific Daylight Time",
+		"America/Bogota"
+	},							/* (GMT-05:00) Bogota, Lima, Quito */
+	{
+		"SA Western Standard Time", "SA Western Daylight Time",
+		"America/Caracas"
+	},							/* (GMT-04:00) Caracas, La Paz */
+	{
+		"Samoa Standard Time", "Samoa Daylight Time",
+		"Pacific/Midway"
+	},							/* (GMT-11:00) Midway Island, Samoa */
+	{
+		"SE Asia Standard Time", "SE Asia Daylight Time",
+		"Asia/Bangkok"
+	},							/* (GMT+07:00) Bangkok, Hanoi, Jakarta */
+	{
+		"Malay Peninsula Standard Time", "Malay Peninsula Daylight Time",
+		"Asia/Kuala_Lumpur"
+	},							/* (GMT+08:00) Kuala Lumpur, Singapore */
+	{
+		"South Africa Standard Time", "South Africa Daylight Time",
+		"Africa/Harare"
+	},							/* (GMT+02:00) Harare, Pretoria */
+	{
+		"Sri Lanka Standard Time", "Sri Lanka Daylight Time",
+		"Asia/Colombo"
+	},							/* (GMT+06:00) Sri Jayawardenepura */
+	{
+		"Taipei Standard Time", "Taipei Daylight Time",
+		"Asia/Taipei"
+	},							/* (GMT+08:00) Taipei */
+	{
+		"Tasmania Standard Time", "Tasmania Daylight Time",
+		"Australia/Hobart"
+	},							/* (GMT+10:00) Hobart */
+	{
+		"Tokyo Standard Time", "Tokyo Daylight Time",
+		"Asia/Tokyo"
+	},							/* (GMT+09:00) Osaka, Sapporo, Tokyo */
+	{
+		"Tonga Standard Time", "Tonga Daylight Time",
+		"Pacific/Tongatapu"
+	},							/* (GMT+13:00) Nuku'alofa */
+	{
+		"Ulaanbaatar Standard Time", "Ulaanbaatar Daylight Time",
+		"Asia/Ulaanbaatar",
+	},							/* (GMT+08:00) Ulaanbaatar */
+	{
+		"US Eastern Standard Time", "US Eastern Daylight Time",
+		"US/Eastern"
+	},							/* (GMT-05:00) Indiana (East) */
+	{
+		"US Mountain Standard Time", "US Mountain Daylight Time",
+		"US/Arizona"
+	},							/* (GMT-07:00) Arizona */
+	{
+		"Coordinated Universal Time", "Coordinated Universal Time",
+		"UTC"
+	},							/* (GMT) Coordinated Universal Time */
+	{
+		"UTC+12", "UTC+12",
+		"Etc/GMT+12"
+	},							/* (GMT+12:00) Coordinated Universal Time+12 */
+	{
+		"UTC-02", "UTC-02",
+		"Etc/GMT-02"
+	},							/* (GMT-02:00) Coordinated Universal Time-02 */
+	{
+		"UTC-11", "UTC-11",
+		"Etc/GMT-11"
+	},							/* (GMT-11:00) Coordinated Universal Time-11 */
+	{
+		"Venezuela Standard Time", "Venezuela Daylight Time",
+		"America/Caracas",
+	},							/* (GMT-04:30) Caracas */
+	{
+		"Vladivostok Standard Time", "Vladivostok Daylight Time",
+		"Asia/Vladivostok"
+	},							/* (GMT+10:00) Vladivostok */
+	{
+		"W. Australia Standard Time", "W. Australia Daylight Time",
+		"Australia/Perth"
+	},							/* (GMT+08:00) Perth */
+#ifdef NOT_USED
+	/* Could not find a match for this one (just a guess). Excluded for now. */
+	{
+		"W. Central Africa Standard Time", "W. Central Africa Daylight Time",
+		"WAT"
+	},							/* (GMT+01:00) West Central Africa */
+#endif
+	{
+		"W. Europe Standard Time", "W. Europe Daylight Time",
+		"CET"
+	},							/* (GMT+01:00) Amsterdam, Berlin, Bern, Rome,
+								 * Stockholm, Vienna */
+	{
+		"West Asia Standard Time", "West Asia Daylight Time",
+		"Asia/Karachi"
+	},							/* (GMT+05:00) Islamabad, Karachi, Tashkent */
+	{
+		"West Pacific Standard Time", "West Pacific Daylight Time",
+		"Pacific/Guam"
+	},							/* (GMT+10:00) Guam, Port Moresby */
+	{
+		"Yakutsk Standard Time", "Yakutsk Daylight Time",
+		"Asia/Yakutsk"
+	},							/* (GMT+09:00) Yakutsk */
+	{
+		NULL, NULL, NULL
+	}
+};
+
+static const char *
+identify_system_timezone(void)
+{
+	int			i;
+	char		tzname[128];
+	char		localtzname[256];
+	time_t		t = time(NULL);
+	struct tm  *tm = localtime(&t);
+	HKEY		rootKey;
+	int			idx;
+
+	if (!tm)
+	{
+#ifdef DEBUG_IDENTIFY_TIMEZONE
+		fprintf(stderr, "could not identify system time zone: localtime() failed\n");
+#endif
+		return NULL;			/* go to GMT */
+	}
+
+	memset(tzname, 0, sizeof(tzname));
+	strftime(tzname, sizeof(tzname) - 1, "%Z", tm);
+
+	for (i = 0; win32_tzmap[i].stdname != NULL; i++)
+	{
+		if (strcmp(tzname, win32_tzmap[i].stdname) == 0 ||
+			strcmp(tzname, win32_tzmap[i].dstname) == 0)
+		{
+#ifdef DEBUG_IDENTIFY_TIMEZONE
+			fprintf(stderr, "TZ \"%s\" matches system time zone \"%s\"\n",
+					win32_tzmap[i].pgtzname, tzname);
+#endif
+			return win32_tzmap[i].pgtzname;
+		}
+	}
+
+	/*
+	 * Localized Windows versions return localized names for the timezone.
+	 * Scan the registry to find the English name, and then try matching
+	 * against our table again.
+	 */
+	memset(localtzname, 0, sizeof(localtzname));
+	if (RegOpenKeyEx(HKEY_LOCAL_MACHINE,
+			   "SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Time Zones",
+					 0,
+					 KEY_READ,
+					 &rootKey) != ERROR_SUCCESS)
+	{
+#ifdef DEBUG_IDENTIFY_TIMEZONE
+		fprintf(stderr, "could not open registry key to identify system time zone: error code %lu\n",
+				GetLastError());
+#endif
+		return NULL;			/* go to GMT */
+	}
+
+	for (idx = 0;; idx++)
+	{
+		char		keyname[256];
+		char		zonename[256];
+		DWORD		namesize;
+		FILETIME	lastwrite;
+		HKEY		key;
+		LONG		r;
+
+		memset(keyname, 0, sizeof(keyname));
+		namesize = sizeof(keyname);
+		if ((r = RegEnumKeyEx(rootKey,
+							  idx,
+							  keyname,
+							  &namesize,
+							  NULL,
+							  NULL,
+							  NULL,
+							  &lastwrite)) != ERROR_SUCCESS)
+		{
+			if (r == ERROR_NO_MORE_ITEMS)
+				break;
+#ifdef DEBUG_IDENTIFY_TIMEZONE
+			fprintf(stderr, "could not enumerate registry subkeys to identify system time zone: %d\n",
+					(int) r);
+#endif
+			break;
+		}
+
+		if ((r = RegOpenKeyEx(rootKey, keyname, 0, KEY_READ, &key)) != ERROR_SUCCESS)
+		{
+#ifdef DEBUG_IDENTIFY_TIMEZONE
+			fprintf(stderr, "could not open registry subkey to identify system time zone: %d\n",
+					(int) r);
+#endif
+			break;
+		}
+
+		memset(zonename, 0, sizeof(zonename));
+		namesize = sizeof(zonename);
+		if ((r = RegQueryValueEx(key, "Std", NULL, NULL, (unsigned char *) zonename, &namesize)) != ERROR_SUCCESS)
+		{
+#ifdef DEBUG_IDENTIFY_TIMEZONE
+			fprintf(stderr, "could not query value for key \"std\" to identify system time zone \"%s\": %d\n",
+					keyname, (int) r);
+#endif
+			RegCloseKey(key);
+			continue;			/* Proceed to look at the next timezone */
+		}
+		if (strcmp(tzname, zonename) == 0)
+		{
+			/* Matched zone */
+			strcpy(localtzname, keyname);
+			RegCloseKey(key);
+			break;
+		}
+		memset(zonename, 0, sizeof(zonename));
+		namesize = sizeof(zonename);
+		if ((r = RegQueryValueEx(key, "Dlt", NULL, NULL, (unsigned char *) zonename, &namesize)) != ERROR_SUCCESS)
+		{
+#ifdef DEBUG_IDENTIFY_TIMEZONE
+			fprintf(stderr, "could not query value for key \"dlt\" to identify system time zone \"%s\": %d\n",
+					keyname, (int) r);
+#endif
+			RegCloseKey(key);
+			continue;			/* Proceed to look at the next timezone */
+		}
+		if (strcmp(tzname, zonename) == 0)
+		{
+			/* Matched DST zone */
+			strcpy(localtzname, keyname);
+			RegCloseKey(key);
+			break;
+		}
+
+		RegCloseKey(key);
+	}
+
+	RegCloseKey(rootKey);
+
+	if (localtzname[0])
+	{
+		/* Found a localized name, so scan for that one too */
+		for (i = 0; win32_tzmap[i].stdname != NULL; i++)
+		{
+			if (strcmp(localtzname, win32_tzmap[i].stdname) == 0 ||
+				strcmp(localtzname, win32_tzmap[i].dstname) == 0)
+			{
+#ifdef DEBUG_IDENTIFY_TIMEZONE
+				fprintf(stderr, "TZ \"%s\" matches localized system time zone \"%s\" (\"%s\")\n",
+						win32_tzmap[i].pgtzname, tzname, localtzname);
+#endif
+				return win32_tzmap[i].pgtzname;
+			}
+		}
+	}
+
+#ifdef DEBUG_IDENTIFY_TIMEZONE
+	fprintf(stderr, "could not find a match for system time zone \"%s\"\n",
+			tzname);
+#endif
+	return NULL;				/* go to GMT */
+}
+#endif   /* WIN32 */
+
+
+/*
+ * Return true if the given zone name is valid and is an "acceptable" zone.
+ */
+static bool
+validate_zone(const char *tzname)
+{
+	pg_tz	   *tz;
+
+	if (!tzname || !tzname[0])
+		return false;
+
+	tz = pg_load_tz(tzname);
+	if (!tz)
+		return false;
+
+	if (!pg_tz_acceptable(tz))
+		return false;
+
+	return true;
+}
+
+/*
+ * Identify a suitable default timezone setting based on the environment.
+ *
+ * The installation share_path must be passed in, as that is the default
+ * location for the timezone database directory.
+ *
+ * We first look to the TZ environment variable.  If not found or not
+ * recognized by our own code, we see if we can identify the timezone
+ * from the behavior of the system timezone library.  When all else fails,
+ * return NULL, indicating that we should default to GMT.
+ */
+const char *
+select_default_timezone(const char *share_path)
+{
+	const char *tzname;
+
+	/* Initialize timezone directory path, if needed */
+#ifndef SYSTEMTZDIR
+	snprintf(tzdirpath, sizeof(tzdirpath), "%s/timezone", share_path);
+#endif
+
+	/* Check TZ environment variable */
+	tzname = getenv("TZ");
+	if (validate_zone(tzname))
+		return tzname;
+
+	/* Nope, so try to identify the system timezone */
+	tzname = identify_system_timezone();
+	if (validate_zone(tzname))
+		return tzname;
+
+	return NULL;
+}
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index 1dbd6f603a3..e535fdad1e9 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -61,6 +61,9 @@
 #include "getopt_long.h"
 #include "miscadmin.h"
 
+/* Ideally this would be in a .h file, but it hardly seems worth the trouble */
+extern const char *select_default_timezone(const char *share_path);
+
 
 /*
  * these values are passed in by makefile defines
@@ -947,8 +950,9 @@ static void
 setup_config(void)
 {
 	char	  **conflines;
-	char		repltok[100];
+	char		repltok[TZ_STRLEN_MAX + 100];
 	char		path[MAXPGPATH];
+	const char *default_timezone;
 
 	fputs(_("creating configuration files ... "), stdout);
 	fflush(stdout);
@@ -1011,6 +1015,17 @@ setup_config(void)
 						 "#default_text_search_config = 'pg_catalog.simple'",
 							  repltok);
 
+	default_timezone = select_default_timezone(share_path);
+	if (default_timezone)
+	{
+		snprintf(repltok, sizeof(repltok), "timezone = '%s'",
+				 escape_quotes(default_timezone));
+		conflines = replace_token(conflines, "#timezone = 'GMT'", repltok);
+		snprintf(repltok, sizeof(repltok), "log_timezone = '%s'",
+				 escape_quotes(default_timezone));
+		conflines = replace_token(conflines, "#log_timezone = 'GMT'", repltok);
+	}
+
 	snprintf(path, sizeof(path), "%s/postgresql.conf", pg_data);
 
 	writefile(path, conflines);
@@ -2796,14 +2811,6 @@ main(int argc, char *argv[])
 	sprintf(pgdenv, "PGDATA=%s", pg_data);
 	putenv(pgdenv);
 
-	/*
-	 * Also ensure that TZ is set, so that we don't waste time identifying the
-	 * system timezone each of the many times we start a standalone backend.
-	 * It's okay to use a hard-wired value here because nothing done during
-	 * initdb cares about the timezone setting.
-	 */
-	putenv("TZ=GMT");
-
 	if ((ret = find_other_exec(argv[0], "postgres", PG_BACKEND_VERSIONSTR,
 							   backend_exec)) < 0)
 	{
diff --git a/src/include/pgtime.h b/src/include/pgtime.h
index e73cfa51a4d..9dc794026c1 100644
--- a/src/include/pgtime.h
+++ b/src/include/pgtime.h
@@ -40,6 +40,11 @@ struct pg_tm
 typedef struct pg_tz pg_tz;
 typedef struct pg_tzenum pg_tzenum;
 
+/* Maximum length of a timezone name (not including trailing null) */
+#define TZ_STRLEN_MAX 255
+
+/* these functions are in localtime.c */
+
 extern struct pg_tm *pg_localtime(const pg_time_t *timep, const pg_tz *tz);
 extern struct pg_tm *pg_gmtime(const pg_time_t *timep);
 extern int pg_next_dst_boundary(const pg_time_t *timep,
@@ -52,22 +57,20 @@ extern int pg_next_dst_boundary(const pg_time_t *timep,
 extern size_t pg_strftime(char *s, size_t max, const char *format,
 			const struct pg_tm * tm);
 
-extern void pg_timezone_pre_initialize(void);
-extern void pg_timezone_initialize(void);
-extern pg_tz *pg_tzset(const char *tzname);
-extern bool tz_acceptable(pg_tz *tz);
 extern bool pg_get_timezone_offset(const pg_tz *tz, long int *gmtoff);
 extern const char *pg_get_timezone_name(pg_tz *tz);
+extern bool pg_tz_acceptable(pg_tz *tz);
 
-extern pg_tzenum *pg_tzenumerate_start(void);
-extern pg_tz *pg_tzenumerate_next(pg_tzenum *dir);
-extern void pg_tzenumerate_end(pg_tzenum *dir);
+/* these functions and variables are in pgtz.c */
 
 extern pg_tz *session_timezone;
 extern pg_tz *log_timezone;
-extern pg_tz *gmt_timezone;
 
-/* Maximum length of a timezone name (not including trailing null) */
-#define TZ_STRLEN_MAX 255
+extern void pg_timezone_initialize(void);
+extern pg_tz *pg_tzset(const char *tzname);
+
+extern pg_tzenum *pg_tzenumerate_start(void);
+extern pg_tz *pg_tzenumerate_next(pg_tzenum *dir);
+extern void pg_tzenumerate_end(pg_tzenum *dir);
 
 #endif   /* _PGTIME_H */
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index 6b3b5c66949..d99d624fae5 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -333,8 +333,6 @@ extern ArrayType *GUCArrayAdd(ArrayType *array, const char *name, const char *va
 extern ArrayType *GUCArrayDelete(ArrayType *array, const char *name);
 extern ArrayType *GUCArrayReset(ArrayType *array);
 
-extern void pg_timezone_abbrev_initialize(void);
-
 #ifdef EXEC_BACKEND
 extern void write_nondefault_variables(GucContext context);
 extern void read_nondefault_variables(void);
diff --git a/src/timezone/localtime.c b/src/timezone/localtime.c
index 782b99adfb7..037cdbbdcd7 100644
--- a/src/timezone/localtime.c
+++ b/src/timezone/localtime.c
@@ -16,6 +16,7 @@
 
 #include <fcntl.h>
 
+#include "datatype/timestamp.h"
 #include "private.h"
 #include "pgtz.h"
 #include "tzfile.h"
@@ -734,6 +735,7 @@ tzparse(const char *name, struct state * sp, int lastditch)
 		 * can't assume pg_open_tzfile() is sane yet, and we don't care about
 		 * leap seconds anyway.
 		 */
+		sp->goback = sp->goahead = FALSE;
 		load_result = -1;
 	}
 	else
@@ -1476,3 +1478,29 @@ pg_get_timezone_name(pg_tz *tz)
 		return tz->TZname;
 	return NULL;
 }
+
+/*
+ * Check whether timezone is acceptable.
+ *
+ * What we are doing here is checking for leap-second-aware timekeeping.
+ * We need to reject such TZ settings because they'll wreak havoc with our
+ * date/time arithmetic.
+ */
+bool
+pg_tz_acceptable(pg_tz *tz)
+{
+	struct pg_tm *tt;
+	pg_time_t	time2000;
+
+	/*
+	 * To detect leap-second timekeeping, run pg_localtime for what should be
+	 * GMT midnight, 2000-01-01.  Insist that the tm_sec value be zero; any
+	 * other result has to be due to leap seconds.
+	 */
+	time2000 = (POSTGRES_EPOCH_JDATE - UNIX_EPOCH_JDATE) * SECS_PER_DAY;
+	tt = pg_localtime(&time2000, tz);
+	if (!tt || tt->tm_sec != 0)
+		return false;
+
+	return true;
+}
diff --git a/src/timezone/pgtz.c b/src/timezone/pgtz.c
index 254ddb8ad63..7063bf458ee 100644
--- a/src/timezone/pgtz.c
+++ b/src/timezone/pgtz.c
@@ -10,8 +10,6 @@
  *
  *-------------------------------------------------------------------------
  */
-#define NO_REDEFINE_TIMEFUNCS
-
 #include "postgres.h"
 
 #include <ctype.h>
@@ -22,28 +20,19 @@
 #include "miscadmin.h"
 #include "pgtz.h"
 #include "storage/fd.h"
-#include "tzfile.h"
-#include "utils/datetime.h"
-#include "utils/guc.h"
 #include "utils/hsearch.h"
 
+
 /* Current session timezone (controlled by TimeZone GUC) */
 pg_tz	   *session_timezone = NULL;
 
 /* Current log timezone (controlled by log_timezone GUC) */
 pg_tz	   *log_timezone = NULL;
 
-/* Fallback GMT timezone for last-ditch error message formatting */
-pg_tz	   *gmt_timezone = NULL;
-static pg_tz gmt_timezone_data;
-
 
 static bool scan_directory_ci(const char *dirname,
 				  const char *fname, int fnamelen,
 				  char *canonname, int canonnamelen);
-static const char *identify_system_timezone(void);
-static pg_tz *get_pg_tz_for_zone(const char *tzname);
-static pg_tz *select_default_timezone(void);
 
 
 /*
@@ -80,7 +69,7 @@ pg_TZDIR(void)
  * timezone database does not contain case-equivalent names).
  *
  * If "canonname" is not NULL, then on success the canonical spelling of the
- * given name is stored there (it is assumed to be > TZ_STRLEN_MAX bytes!).
+ * given name is stored there (the buffer must be > TZ_STRLEN_MAX bytes!).
  */
 int
 pg_open_tzfile(const char *name, char *canonname)
@@ -175,1054 +164,6 @@ scan_directory_ci(const char *dirname, const char *fname, int fnamelen,
 }
 
 
-/*
- * The following block of code attempts to determine which timezone in our
- * timezone database is the best match for the active system timezone.
- *
- * On most systems, we rely on trying to match the observable behavior of
- * the C library's localtime() function.  The database zone that matches
- * furthest into the past is the one to use.  Often there will be several
- * zones with identical rankings (since the zic database assigns multiple
- * names to many zones).  We break ties arbitrarily by preferring shorter,
- * then alphabetically earlier zone names.
- *
- * Win32's native knowledge about timezones appears to be too incomplete
- * and too different from the zic database for the above matching strategy
- * to be of any use. But there is just a limited number of timezones
- * available, so we can rely on a handmade mapping table instead.
- */
-
-#ifndef WIN32
-
-#define T_DAY	((time_t) (60*60*24))
-#define T_WEEK	((time_t) (60*60*24*7))
-#define T_MONTH ((time_t) (60*60*24*31))
-
-#define MAX_TEST_TIMES (52*100) /* 100 years */
-
-struct tztry
-{
-	int			n_test_times;
-	time_t		test_times[MAX_TEST_TIMES];
-};
-
-static void scan_available_timezones(char *tzdir, char *tzdirsub,
-						 struct tztry * tt,
-						 int *bestscore, char *bestzonename);
-
-
-/*
- * Get GMT offset from a system struct tm
- */
-static int
-get_timezone_offset(struct tm * tm)
-{
-#if defined(HAVE_STRUCT_TM_TM_ZONE)
-	return tm->tm_gmtoff;
-#elif defined(HAVE_INT_TIMEZONE)
-	return -TIMEZONE_GLOBAL;
-#else
-#error No way to determine TZ? Can this happen?
-#endif
-}
-
-/*
- * Convenience subroutine to convert y/m/d to time_t (NOT pg_time_t)
- */
-static time_t
-build_time_t(int year, int month, int day)
-{
-	struct tm	tm;
-
-	memset(&tm, 0, sizeof(tm));
-	tm.tm_mday = day;
-	tm.tm_mon = month - 1;
-	tm.tm_year = year - 1900;
-
-	return mktime(&tm);
-}
-
-/*
- * Does a system tm value match one we computed ourselves?
- */
-static bool
-compare_tm(struct tm * s, struct pg_tm * p)
-{
-	if (s->tm_sec != p->tm_sec ||
-		s->tm_min != p->tm_min ||
-		s->tm_hour != p->tm_hour ||
-		s->tm_mday != p->tm_mday ||
-		s->tm_mon != p->tm_mon ||
-		s->tm_year != p->tm_year ||
-		s->tm_wday != p->tm_wday ||
-		s->tm_yday != p->tm_yday ||
-		s->tm_isdst != p->tm_isdst)
-		return false;
-	return true;
-}
-
-/*
- * See how well a specific timezone setting matches the system behavior
- *
- * We score a timezone setting according to the number of test times it
- * matches.  (The test times are ordered later-to-earlier, but this routine
- * doesn't actually know that; it just scans until the first non-match.)
- *
- * We return -1 for a completely unusable setting; this is worse than the
- * score of zero for a setting that works but matches not even the first
- * test time.
- */
-static int
-score_timezone(const char *tzname, struct tztry * tt)
-{
-	int			i;
-	pg_time_t	pgtt;
-	struct tm  *systm;
-	struct pg_tm *pgtm;
-	char		cbuf[TZ_STRLEN_MAX + 1];
-	pg_tz		tz;
-
-
-	/*
-	 * Load timezone directly. Don't use pg_tzset, because we don't want all
-	 * timezones loaded in the cache at startup.
-	 */
-	if (tzload(tzname, NULL, &tz.state, TRUE) != 0)
-	{
-		if (tzname[0] == ':' || tzparse(tzname, &tz.state, FALSE) != 0)
-		{
-			return -1;			/* can't handle the TZ name at all */
-		}
-	}
-
-	/* Reject if leap seconds involved */
-	if (!tz_acceptable(&tz))
-	{
-		elog(DEBUG4, "Reject TZ \"%s\": uses leap seconds", tzname);
-		return -1;
-	}
-
-	/* Check for match at all the test times */
-	for (i = 0; i < tt->n_test_times; i++)
-	{
-		pgtt = (pg_time_t) (tt->test_times[i]);
-		pgtm = pg_localtime(&pgtt, &tz);
-		if (!pgtm)
-			return -1;			/* probably shouldn't happen */
-		systm = localtime(&(tt->test_times[i]));
-		if (!systm)
-		{
-			elog(DEBUG4, "TZ \"%s\" scores %d: at %ld %04d-%02d-%02d %02d:%02d:%02d %s, system had no data",
-				 tzname, i, (long) pgtt,
-				 pgtm->tm_year + 1900, pgtm->tm_mon + 1, pgtm->tm_mday,
-				 pgtm->tm_hour, pgtm->tm_min, pgtm->tm_sec,
-				 pgtm->tm_isdst ? "dst" : "std");
-			return i;
-		}
-		if (!compare_tm(systm, pgtm))
-		{
-			elog(DEBUG4, "TZ \"%s\" scores %d: at %ld %04d-%02d-%02d %02d:%02d:%02d %s versus %04d-%02d-%02d %02d:%02d:%02d %s",
-				 tzname, i, (long) pgtt,
-				 pgtm->tm_year + 1900, pgtm->tm_mon + 1, pgtm->tm_mday,
-				 pgtm->tm_hour, pgtm->tm_min, pgtm->tm_sec,
-				 pgtm->tm_isdst ? "dst" : "std",
-				 systm->tm_year + 1900, systm->tm_mon + 1, systm->tm_mday,
-				 systm->tm_hour, systm->tm_min, systm->tm_sec,
-				 systm->tm_isdst ? "dst" : "std");
-			return i;
-		}
-		if (systm->tm_isdst >= 0)
-		{
-			/* Check match of zone names, too */
-			if (pgtm->tm_zone == NULL)
-				return -1;		/* probably shouldn't happen */
-			memset(cbuf, 0, sizeof(cbuf));
-			strftime(cbuf, sizeof(cbuf) - 1, "%Z", systm);		/* zone abbr */
-			if (strcmp(cbuf, pgtm->tm_zone) != 0)
-			{
-				elog(DEBUG4, "TZ \"%s\" scores %d: at %ld \"%s\" versus \"%s\"",
-					 tzname, i, (long) pgtt,
-					 pgtm->tm_zone, cbuf);
-				return i;
-			}
-		}
-	}
-
-	elog(DEBUG4, "TZ \"%s\" gets max score %d", tzname, i);
-	return i;
-}
-
-
-/*
- * Try to identify a timezone name (in our terminology) that best matches the
- * observed behavior of the system timezone library.  We cannot assume that
- * the system TZ environment setting (if indeed there is one) matches our
- * terminology, so we ignore it and just look at what localtime() returns.
- */
-static const char *
-identify_system_timezone(void)
-{
-	static char resultbuf[TZ_STRLEN_MAX + 1];
-	time_t		tnow;
-	time_t		t;
-	struct tztry tt;
-	struct tm  *tm;
-	int			thisyear;
-	int			bestscore;
-	char		tmptzdir[MAXPGPATH];
-	int			std_ofs;
-	char		std_zone_name[TZ_STRLEN_MAX + 1],
-				dst_zone_name[TZ_STRLEN_MAX + 1];
-	char		cbuf[TZ_STRLEN_MAX + 1];
-
-	/* Initialize OS timezone library */
-	tzset();
-
-	/*
-	 * Set up the list of dates to be probed to see how well our timezone
-	 * matches the system zone.  We first probe January and July of the
-	 * current year; this serves to quickly eliminate the vast majority of the
-	 * TZ database entries.  If those dates match, we probe every week for 100
-	 * years backwards from the current July.  (Weekly resolution is good
-	 * enough to identify DST transition rules, since everybody switches on
-	 * Sundays.)  This is sufficient to cover most of the Unix time_t range,
-	 * and we don't want to look further than that since many systems won't
-	 * have sane TZ behavior further back anyway.  The further back the zone
-	 * matches, the better we score it.  This may seem like a rather random
-	 * way of doing things, but experience has shown that system-supplied
-	 * timezone definitions are likely to have DST behavior that is right for
-	 * the recent past and not so accurate further back. Scoring in this way
-	 * allows us to recognize zones that have some commonality with the zic
-	 * database, without insisting on exact match. (Note: we probe Thursdays,
-	 * not Sundays, to avoid triggering DST-transition bugs in localtime
-	 * itself.)
-	 */
-	tnow = time(NULL);
-	tm = localtime(&tnow);
-	if (!tm)
-		return NULL;			/* give up if localtime is broken... */
-	thisyear = tm->tm_year + 1900;
-
-	t = build_time_t(thisyear, 1, 15);
-
-	/*
-	 * Round back to GMT midnight Thursday.  This depends on the knowledge
-	 * that the time_t origin is Thu Jan 01 1970.  (With a different origin
-	 * we'd be probing some other day of the week, but it wouldn't matter
-	 * anyway unless localtime() had DST-transition bugs.)
-	 */
-	t -= (t % T_WEEK);
-
-	tt.n_test_times = 0;
-	tt.test_times[tt.n_test_times++] = t;
-
-	t = build_time_t(thisyear, 7, 15);
-	t -= (t % T_WEEK);
-
-	tt.test_times[tt.n_test_times++] = t;
-
-	while (tt.n_test_times < MAX_TEST_TIMES)
-	{
-		t -= T_WEEK;
-		tt.test_times[tt.n_test_times++] = t;
-	}
-
-	/* Search for the best-matching timezone file */
-	strcpy(tmptzdir, pg_TZDIR());
-	bestscore = -1;
-	resultbuf[0] = '\0';
-	scan_available_timezones(tmptzdir, tmptzdir + strlen(tmptzdir) + 1,
-							 &tt,
-							 &bestscore, resultbuf);
-	if (bestscore > 0)
-	{
-		/* Ignore zic's rather silly "Factory" time zone; use GMT instead */
-		if (strcmp(resultbuf, "Factory") == 0)
-			return NULL;
-		return resultbuf;
-	}
-
-	/*
-	 * Couldn't find a match in the database, so next we try constructed zone
-	 * names (like "PST8PDT").
-	 *
-	 * First we need to determine the names of the local standard and daylight
-	 * zones.  The idea here is to scan forward from today until we have seen
-	 * both zones, if both are in use.
-	 */
-	memset(std_zone_name, 0, sizeof(std_zone_name));
-	memset(dst_zone_name, 0, sizeof(dst_zone_name));
-	std_ofs = 0;
-
-	tnow = time(NULL);
-
-	/*
-	 * Round back to a GMT midnight so results don't depend on local time of
-	 * day
-	 */
-	tnow -= (tnow % T_DAY);
-
-	/*
-	 * We have to look a little further ahead than one year, in case today is
-	 * just past a DST boundary that falls earlier in the year than the next
-	 * similar boundary.  Arbitrarily scan up to 14 months.
-	 */
-	for (t = tnow; t <= tnow + T_MONTH * 14; t += T_MONTH)
-	{
-		tm = localtime(&t);
-		if (!tm)
-			continue;
-		if (tm->tm_isdst < 0)
-			continue;
-		if (tm->tm_isdst == 0 && std_zone_name[0] == '\0')
-		{
-			/* found STD zone */
-			memset(cbuf, 0, sizeof(cbuf));
-			strftime(cbuf, sizeof(cbuf) - 1, "%Z", tm); /* zone abbr */
-			strcpy(std_zone_name, cbuf);
-			std_ofs = get_timezone_offset(tm);
-		}
-		if (tm->tm_isdst > 0 && dst_zone_name[0] == '\0')
-		{
-			/* found DST zone */
-			memset(cbuf, 0, sizeof(cbuf));
-			strftime(cbuf, sizeof(cbuf) - 1, "%Z", tm); /* zone abbr */
-			strcpy(dst_zone_name, cbuf);
-		}
-		/* Done if found both */
-		if (std_zone_name[0] && dst_zone_name[0])
-			break;
-	}
-
-	/* We should have found a STD zone name by now... */
-	if (std_zone_name[0] == '\0')
-	{
-		ereport(LOG,
-				(errmsg("could not determine system time zone"),
-				 errdetail("The PostgreSQL time zone will be set to \"%s\".",
-						   "GMT"),
-		errhint("You can specify the correct timezone in postgresql.conf.")));
-		return NULL;			/* go to GMT */
-	}
-
-	/* If we found DST then try STD<ofs>DST */
-	if (dst_zone_name[0] != '\0')
-	{
-		snprintf(resultbuf, sizeof(resultbuf), "%s%d%s",
-				 std_zone_name, -std_ofs / 3600, dst_zone_name);
-		if (score_timezone(resultbuf, &tt) > 0)
-			return resultbuf;
-	}
-
-	/* Try just the STD timezone (works for GMT at least) */
-	strcpy(resultbuf, std_zone_name);
-	if (score_timezone(resultbuf, &tt) > 0)
-		return resultbuf;
-
-	/* Try STD<ofs> */
-	snprintf(resultbuf, sizeof(resultbuf), "%s%d",
-			 std_zone_name, -std_ofs / 3600);
-	if (score_timezone(resultbuf, &tt) > 0)
-		return resultbuf;
-
-	/*
-	 * Did not find the timezone.  Fallback to use a GMT zone.	Note that the
-	 * zic timezone database names the GMT-offset zones in POSIX style: plus
-	 * is west of Greenwich.  It's unfortunate that this is opposite of SQL
-	 * conventions.  Should we therefore change the names? Probably not...
-	 */
-	snprintf(resultbuf, sizeof(resultbuf), "Etc/GMT%s%d",
-			 (-std_ofs > 0) ? "+" : "", -std_ofs / 3600);
-
-	ereport(LOG,
-			(errmsg("could not recognize system time zone"),
-			 errdetail("The PostgreSQL time zone will be set to \"%s\".",
-					   resultbuf),
-	   errhint("You can specify the correct timezone in postgresql.conf.")));
-	return resultbuf;
-}
-
-/*
- * Recursively scan the timezone database looking for the best match to
- * the system timezone behavior.
- *
- * tzdir points to a buffer of size MAXPGPATH.	On entry, it holds the
- * pathname of a directory containing TZ files.  We internally modify it
- * to hold pathnames of sub-directories and files, but must restore it
- * to its original contents before exit.
- *
- * tzdirsub points to the part of tzdir that represents the subfile name
- * (ie, tzdir + the original directory name length, plus one for the
- * first added '/').
- *
- * tt tells about the system timezone behavior we need to match.
- *
- * *bestscore and *bestzonename on entry hold the best score found so far
- * and the name of the best zone.  We overwrite them if we find a better
- * score.  bestzonename must be a buffer of length TZ_STRLEN_MAX + 1.
- */
-static void
-scan_available_timezones(char *tzdir, char *tzdirsub, struct tztry * tt,
-						 int *bestscore, char *bestzonename)
-{
-	int			tzdir_orig_len = strlen(tzdir);
-	DIR		   *dirdesc;
-	struct dirent *direntry;
-
-	dirdesc = AllocateDir(tzdir);
-	if (!dirdesc)
-	{
-		ereport(LOG,
-				(errcode_for_file_access(),
-				 errmsg("could not open directory \"%s\": %m", tzdir)));
-		return;
-	}
-
-	while ((direntry = ReadDir(dirdesc, tzdir)) != NULL)
-	{
-		struct stat statbuf;
-
-		/* Ignore . and .., plus any other "hidden" files */
-		if (direntry->d_name[0] == '.')
-			continue;
-
-		snprintf(tzdir + tzdir_orig_len, MAXPGPATH - tzdir_orig_len,
-				 "/%s", direntry->d_name);
-
-		if (stat(tzdir, &statbuf) != 0)
-		{
-			ereport(LOG,
-					(errcode_for_file_access(),
-					 errmsg("could not stat \"%s\": %m", tzdir)));
-			tzdir[tzdir_orig_len] = '\0';
-			continue;
-		}
-
-		if (S_ISDIR(statbuf.st_mode))
-		{
-			/* Recurse into subdirectory */
-			scan_available_timezones(tzdir, tzdirsub, tt,
-									 bestscore, bestzonename);
-		}
-		else
-		{
-			/* Load and test this file */
-			int			score = score_timezone(tzdirsub, tt);
-
-			if (score > *bestscore)
-			{
-				*bestscore = score;
-				strlcpy(bestzonename, tzdirsub, TZ_STRLEN_MAX + 1);
-			}
-			else if (score == *bestscore)
-			{
-				/* Consider how to break a tie */
-				if (strlen(tzdirsub) < strlen(bestzonename) ||
-					(strlen(tzdirsub) == strlen(bestzonename) &&
-					 strcmp(tzdirsub, bestzonename) < 0))
-					strlcpy(bestzonename, tzdirsub, TZ_STRLEN_MAX + 1);
-			}
-		}
-
-		/* Restore tzdir */
-		tzdir[tzdir_orig_len] = '\0';
-	}
-
-	FreeDir(dirdesc);
-}
-#else							/* WIN32 */
-
-static const struct
-{
-	const char *stdname;		/* Windows name of standard timezone */
-	const char *dstname;		/* Windows name of daylight timezone */
-	const char *pgtzname;		/* Name of pgsql timezone to map to */
-}	win32_tzmap[] =
-
-{
-	/*
-	 * This list was built from the contents of the registry at
-	 * HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time
-	 * Zones on Windows 2003 R2.
-	 *
-	 * The zones have been matched to zic timezones by looking at the cities
-	 * listed in the win32 display name (in the comment here) in most cases.
-	 */
-	{
-		"Afghanistan Standard Time", "Afghanistan Daylight Time",
-		"Asia/Kabul"
-	},							/* (GMT+04:30) Kabul */
-	{
-		"Alaskan Standard Time", "Alaskan Daylight Time",
-		"US/Alaska"
-	},							/* (GMT-09:00) Alaska */
-	{
-		"Arab Standard Time", "Arab Daylight Time",
-		"Asia/Kuwait"
-	},							/* (GMT+03:00) Kuwait, Riyadh */
-	{
-		"Arabian Standard Time", "Arabian Daylight Time",
-		"Asia/Muscat"
-	},							/* (GMT+04:00) Abu Dhabi, Muscat */
-	{
-		"Arabic Standard Time", "Arabic Daylight Time",
-		"Asia/Baghdad"
-	},							/* (GMT+03:00) Baghdad */
-	{
-		"Argentina Standard Time", "Argentina Daylight Time",
-		"America/Buenos_Aires"
-	},							/* (GMT-03:00) Buenos Aires */
-	{
-		"Armenian Standard Time", "Armenian Daylight Time",
-		"Asia/Yerevan"
-	},							/* (GMT+04:00) Yerevan */
-	{
-		"Atlantic Standard Time", "Atlantic Daylight Time",
-		"Canada/Atlantic"
-	},							/* (GMT-04:00) Atlantic Time (Canada) */
-	{
-		"AUS Central Standard Time", "AUS Central Daylight Time",
-		"Australia/Darwin"
-	},							/* (GMT+09:30) Darwin */
-	{
-		"AUS Eastern Standard Time", "AUS Eastern Daylight Time",
-		"Australia/Canberra"
-	},							/* (GMT+10:00) Canberra, Melbourne, Sydney */
-	{
-		"Azerbaijan Standard Time", "Azerbaijan Daylight Time",
-		"Asia/Baku"
-	},							/* (GMT+04:00) Baku */
-	{
-		"Azores Standard Time", "Azores Daylight Time",
-		"Atlantic/Azores"
-	},							/* (GMT-01:00) Azores */
-	{
-		"Bangladesh Standard Time", "Bangladesh Daylight Time",
-		"Asia/Dhaka"
-	},							/* (GMT+06:00) Dhaka */
-	{
-		"Canada Central Standard Time", "Canada Central Daylight Time",
-		"Canada/Saskatchewan"
-	},							/* (GMT-06:00) Saskatchewan */
-	{
-		"Cape Verde Standard Time", "Cape Verde Daylight Time",
-		"Atlantic/Cape_Verde"
-	},							/* (GMT-01:00) Cape Verde Is. */
-	{
-		"Caucasus Standard Time", "Caucasus Daylight Time",
-		"Asia/Baku"
-	},							/* (GMT+04:00) Baku, Tbilisi, Yerevan */
-	{
-		"Cen. Australia Standard Time", "Cen. Australia Daylight Time",
-		"Australia/Adelaide"
-	},							/* (GMT+09:30) Adelaide */
-	{
-		"Central America Standard Time", "Central America Daylight Time",
-		"CST6CDT"
-	},							/* (GMT-06:00) Central America */
-	{
-		"Central Asia Standard Time", "Central Asia Daylight Time",
-		"Asia/Dhaka"
-	},							/* (GMT+06:00) Astana, Dhaka */
-	{
-		"Central Brazilian Standard Time", "Central Brazilian Daylight Time",
-		"America/Cuiaba"
-	},							/* (GMT-04:00) Cuiaba */
-	{
-		"Central Europe Standard Time", "Central Europe Daylight Time",
-		"Europe/Belgrade"
-	},							/* (GMT+01:00) Belgrade, Bratislava, Budapest,
-								 * Ljubljana, Prague */
-	{
-		"Central European Standard Time", "Central European Daylight Time",
-		"Europe/Sarajevo"
-	},							/* (GMT+01:00) Sarajevo, Skopje, Warsaw,
-								 * Zagreb */
-	{
-		"Central Pacific Standard Time", "Central Pacific Daylight Time",
-		"Pacific/Noumea"
-	},							/* (GMT+11:00) Magadan, Solomon Is., New
-								 * Caledonia */
-	{
-		"Central Standard Time", "Central Daylight Time",
-		"US/Central"
-	},							/* (GMT-06:00) Central Time (US & Canada) */
-	{
-		"Central Standard Time (Mexico)", "Central Daylight Time (Mexico)",
-		"America/Mexico_City"
-	},							/* (GMT-06:00) Guadalajara, Mexico City,
-								 * Monterrey - New */
-	{
-		"China Standard Time", "China Daylight Time",
-		"Asia/Hong_Kong"
-	},							/* (GMT+08:00) Beijing, Chongqing, Hong Kong,
-								 * Urumqi */
-	{
-		"Dateline Standard Time", "Dateline Daylight Time",
-		"Etc/GMT+12"
-	},							/* (GMT-12:00) International Date Line West */
-	{
-		"E. Africa Standard Time", "E. Africa Daylight Time",
-		"Africa/Nairobi"
-	},							/* (GMT+03:00) Nairobi */
-	{
-		"E. Australia Standard Time", "E. Australia Daylight Time",
-		"Australia/Brisbane"
-	},							/* (GMT+10:00) Brisbane */
-	{
-		"E. Europe Standard Time", "E. Europe Daylight Time",
-		"Europe/Bucharest"
-	},							/* (GMT+02:00) Bucharest */
-	{
-		"E. South America Standard Time", "E. South America Daylight Time",
-		"America/Araguaina"
-	},							/* (GMT-03:00) Brasilia */
-	{
-		"Eastern Standard Time", "Eastern Daylight Time",
-		"US/Eastern"
-	},							/* (GMT-05:00) Eastern Time (US & Canada) */
-	{
-		"Egypt Standard Time", "Egypt Daylight Time",
-		"Africa/Cairo"
-	},							/* (GMT+02:00) Cairo */
-	{
-		"Ekaterinburg Standard Time", "Ekaterinburg Daylight Time",
-		"Asia/Yekaterinburg"
-	},							/* (GMT+05:00) Ekaterinburg */
-	{
-		"Fiji Standard Time", "Fiji Daylight Time",
-		"Pacific/Fiji"
-	},							/* (GMT+12:00) Fiji, Kamchatka, Marshall Is. */
-	{
-		"FLE Standard Time", "FLE Daylight Time",
-		"Europe/Helsinki"
-	},							/* (GMT+02:00) Helsinki, Kyiv, Riga, Sofia,
-								 * Tallinn, Vilnius */
-	{
-		"Georgian Standard Time", "Georgian Daylight Time",
-		"Asia/Tbilisi"
-	},							/* (GMT+03:00) Tbilisi */
-	{
-		"GMT Standard Time", "GMT Daylight Time",
-		"Europe/London"
-	},							/* (GMT) Greenwich Mean Time : Dublin,
-								 * Edinburgh, Lisbon, London */
-	{
-		"Greenland Standard Time", "Greenland Daylight Time",
-		"America/Godthab"
-	},							/* (GMT-03:00) Greenland */
-	{
-		"Greenwich Standard Time", "Greenwich Daylight Time",
-		"Africa/Casablanca"
-	},							/* (GMT) Casablanca, Monrovia */
-	{
-		"GTB Standard Time", "GTB Daylight Time",
-		"Europe/Athens"
-	},							/* (GMT+02:00) Athens, Istanbul, Minsk */
-	{
-		"Hawaiian Standard Time", "Hawaiian Daylight Time",
-		"US/Hawaii"
-	},							/* (GMT-10:00) Hawaii */
-	{
-		"India Standard Time", "India Daylight Time",
-		"Asia/Calcutta"
-	},							/* (GMT+05:30) Chennai, Kolkata, Mumbai, New
-								 * Delhi */
-	{
-		"Iran Standard Time", "Iran Daylight Time",
-		"Asia/Tehran"
-	},							/* (GMT+03:30) Tehran */
-	{
-		"Jerusalem Standard Time", "Jerusalem Daylight Time",
-		"Asia/Jerusalem"
-	},							/* (GMT+02:00) Jerusalem */
-	{
-		"Jordan Standard Time", "Jordan Daylight Time",
-		"Asia/Amman"
-	},							/* (GMT+02:00) Amman */
-	{
-		"Kamchatka Standard Time", "Kamchatka Daylight Time",
-		"Asia/Kamchatka"
-	},							/* (GMT+12:00) Petropavlovsk-Kamchatsky */
-	{
-		"Korea Standard Time", "Korea Daylight Time",
-		"Asia/Seoul"
-	},							/* (GMT+09:00) Seoul */
-	{
-		"Mauritius Standard Time", "Mauritius Daylight Time",
-		"Indian/Mauritius"
-	},							/* (GMT+04:00) Port Louis */
-	{
-		"Mexico Standard Time", "Mexico Daylight Time",
-		"America/Mexico_City"
-	},							/* (GMT-06:00) Guadalajara, Mexico City,
-								 * Monterrey */
-	{
-		"Mexico Standard Time 2", "Mexico Daylight Time 2",
-		"America/Chihuahua"
-	},							/* (GMT-07:00) Chihuahua, La Paz, Mazatlan */
-	{
-		"Mid-Atlantic Standard Time", "Mid-Atlantic Daylight Time",
-		"Atlantic/South_Georgia"
-	},							/* (GMT-02:00) Mid-Atlantic */
-	{
-		"Middle East Standard Time", "Middle East Daylight Time",
-		"Asia/Beirut"
-	},							/* (GMT+02:00) Beirut */
-	{
-		"Montevideo Standard Time", "Montevideo Daylight Time",
-		"America/Montevideo"
-	},							/* (GMT-03:00) Montevideo */
-	{
-		"Morocco Standard Time", "Morocco Daylight Time",
-		"Africa/Casablanca"
-	},							/* (GMT) Casablanca */
-	{
-		"Mountain Standard Time", "Mountain Daylight Time",
-		"US/Mountain"
-	},							/* (GMT-07:00) Mountain Time (US & Canada) */
-	{
-		"Mountain Standard Time (Mexico)", "Mountain Daylight Time (Mexico)",
-		"America/Chihuahua"
-	},							/* (GMT-07:00) Chihuahua, La Paz, Mazatlan -
-								 * New */
-	{
-		"Myanmar Standard Time", "Myanmar Daylight Time",
-		"Asia/Rangoon"
-	},							/* (GMT+06:30) Rangoon */
-	{
-		"N. Central Asia Standard Time", "N. Central Asia Daylight Time",
-		"Asia/Novosibirsk"
-	},							/* (GMT+06:00) Novosibirsk */
-	{
-		"Namibia Standard Time", "Namibia Daylight Time",
-		"Africa/Windhoek"
-	},							/* (GMT+02:00) Windhoek */
-	{
-		"Nepal Standard Time", "Nepal Daylight Time",
-		"Asia/Katmandu"
-	},							/* (GMT+05:45) Kathmandu */
-	{
-		"New Zealand Standard Time", "New Zealand Daylight Time",
-		"Pacific/Auckland"
-	},							/* (GMT+12:00) Auckland, Wellington */
-	{
-		"Newfoundland Standard Time", "Newfoundland Daylight Time",
-		"Canada/Newfoundland"
-	},							/* (GMT-03:30) Newfoundland */
-	{
-		"North Asia East Standard Time", "North Asia East Daylight Time",
-		"Asia/Irkutsk"
-	},							/* (GMT+08:00) Irkutsk, Ulaan Bataar */
-	{
-		"North Asia Standard Time", "North Asia Daylight Time",
-		"Asia/Krasnoyarsk"
-	},							/* (GMT+07:00) Krasnoyarsk */
-	{
-		"Pacific SA Standard Time", "Pacific SA Daylight Time",
-		"America/Santiago"
-	},							/* (GMT-04:00) Santiago */
-	{
-		"Pacific Standard Time", "Pacific Daylight Time",
-		"US/Pacific"
-	},							/* (GMT-08:00) Pacific Time (US & Canada);
-								 * Tijuana */
-	{
-		"Pacific Standard Time (Mexico)", "Pacific Daylight Time (Mexico)",
-		"America/Tijuana"
-	},							/* (GMT-08:00) Tijuana, Baja California */
-	{
-		"Pakistan Standard Time", "Pakistan Daylight Time",
-		"Asia/Karachi"
-	},							/* (GMT+05:00) Islamabad, Karachi */
-	{
-		"Paraguay Standard Time", "Paraguay Daylight Time",
-		"America/Asuncion"
-	},							/* (GMT-04:00) Asuncion */
-	{
-		"Romance Standard Time", "Romance Daylight Time",
-		"Europe/Brussels"
-	},							/* (GMT+01:00) Brussels, Copenhagen, Madrid,
-								 * Paris */
-	{
-		"Russian Standard Time", "Russian Daylight Time",
-		"Europe/Moscow"
-	},							/* (GMT+03:00) Moscow, St. Petersburg,
-								 * Volgograd */
-	{
-		"SA Eastern Standard Time", "SA Eastern Daylight Time",
-		"America/Buenos_Aires"
-	},							/* (GMT-03:00) Buenos Aires, Georgetown */
-	{
-		"SA Pacific Standard Time", "SA Pacific Daylight Time",
-		"America/Bogota"
-	},							/* (GMT-05:00) Bogota, Lima, Quito */
-	{
-		"SA Western Standard Time", "SA Western Daylight Time",
-		"America/Caracas"
-	},							/* (GMT-04:00) Caracas, La Paz */
-	{
-		"Samoa Standard Time", "Samoa Daylight Time",
-		"Pacific/Midway"
-	},							/* (GMT-11:00) Midway Island, Samoa */
-	{
-		"SE Asia Standard Time", "SE Asia Daylight Time",
-		"Asia/Bangkok"
-	},							/* (GMT+07:00) Bangkok, Hanoi, Jakarta */
-	{
-		"Malay Peninsula Standard Time", "Malay Peninsula Daylight Time",
-		"Asia/Kuala_Lumpur"
-	},							/* (GMT+08:00) Kuala Lumpur, Singapore */
-	{
-		"South Africa Standard Time", "South Africa Daylight Time",
-		"Africa/Harare"
-	},							/* (GMT+02:00) Harare, Pretoria */
-	{
-		"Sri Lanka Standard Time", "Sri Lanka Daylight Time",
-		"Asia/Colombo"
-	},							/* (GMT+06:00) Sri Jayawardenepura */
-	{
-		"Taipei Standard Time", "Taipei Daylight Time",
-		"Asia/Taipei"
-	},							/* (GMT+08:00) Taipei */
-	{
-		"Tasmania Standard Time", "Tasmania Daylight Time",
-		"Australia/Hobart"
-	},							/* (GMT+10:00) Hobart */
-	{
-		"Tokyo Standard Time", "Tokyo Daylight Time",
-		"Asia/Tokyo"
-	},							/* (GMT+09:00) Osaka, Sapporo, Tokyo */
-	{
-		"Tonga Standard Time", "Tonga Daylight Time",
-		"Pacific/Tongatapu"
-	},							/* (GMT+13:00) Nuku'alofa */
-	{
-		"Ulaanbaatar Standard Time", "Ulaanbaatar Daylight Time",
-		"Asia/Ulaanbaatar",
-	},							/* (GMT+08:00) Ulaanbaatar */
-	{
-		"US Eastern Standard Time", "US Eastern Daylight Time",
-		"US/Eastern"
-	},							/* (GMT-05:00) Indiana (East) */
-	{
-		"US Mountain Standard Time", "US Mountain Daylight Time",
-		"US/Arizona"
-	},							/* (GMT-07:00) Arizona */
-	{
-		"Coordinated Universal Time", "Coordinated Universal Time",
-		"UTC"
-	},							/* (GMT) Coordinated Universal Time */
-	{
-		"UTC+12", "UTC+12",
-		"Etc/GMT+12"
-	},							/* (GMT+12:00) Coordinated Universal Time+12 */
-	{
-		"UTC-02", "UTC-02",
-		"Etc/GMT-02"
-	},							/* (GMT-02:00) Coordinated Universal Time-02 */
-	{
-		"UTC-11", "UTC-11",
-		"Etc/GMT-11"
-	},							/* (GMT-11:00) Coordinated Universal Time-11 */
-	{
-		"Venezuela Standard Time", "Venezuela Daylight Time",
-		"America/Caracas",
-	},							/* (GMT-04:30) Caracas */
-	{
-		"Vladivostok Standard Time", "Vladivostok Daylight Time",
-		"Asia/Vladivostok"
-	},							/* (GMT+10:00) Vladivostok */
-	{
-		"W. Australia Standard Time", "W. Australia Daylight Time",
-		"Australia/Perth"
-	},							/* (GMT+08:00) Perth */
-#ifdef NOT_USED
-	/* Could not find a match for this one (just a guess). Excluded for now. */
-	{
-		"W. Central Africa Standard Time", "W. Central Africa Daylight Time",
-		"WAT"
-	},							/* (GMT+01:00) West Central Africa */
-#endif
-	{
-		"W. Europe Standard Time", "W. Europe Daylight Time",
-		"CET"
-	},							/* (GMT+01:00) Amsterdam, Berlin, Bern, Rome,
-								 * Stockholm, Vienna */
-	{
-		"West Asia Standard Time", "West Asia Daylight Time",
-		"Asia/Karachi"
-	},							/* (GMT+05:00) Islamabad, Karachi, Tashkent */
-	{
-		"West Pacific Standard Time", "West Pacific Daylight Time",
-		"Pacific/Guam"
-	},							/* (GMT+10:00) Guam, Port Moresby */
-	{
-		"Yakutsk Standard Time", "Yakutsk Daylight Time",
-		"Asia/Yakutsk"
-	},							/* (GMT+09:00) Yakutsk */
-	{
-		NULL, NULL, NULL
-	}
-};
-
-static const char *
-identify_system_timezone(void)
-{
-	int			i;
-	char		tzname[128];
-	char		localtzname[256];
-	time_t		t = time(NULL);
-	struct tm  *tm = localtime(&t);
-	HKEY		rootKey;
-	int			idx;
-
-	if (!tm)
-	{
-		ereport(LOG,
-		  (errmsg("could not identify system time zone: localtime() failed"),
-		   errdetail("The PostgreSQL time zone will be set to \"%s\".",
-					 "GMT"),
-		errhint("You can specify the correct timezone in postgresql.conf.")));
-		return NULL;			/* go to GMT */
-	}
-
-	memset(tzname, 0, sizeof(tzname));
-	strftime(tzname, sizeof(tzname) - 1, "%Z", tm);
-
-	for (i = 0; win32_tzmap[i].stdname != NULL; i++)
-	{
-		if (strcmp(tzname, win32_tzmap[i].stdname) == 0 ||
-			strcmp(tzname, win32_tzmap[i].dstname) == 0)
-		{
-			elog(DEBUG4, "TZ \"%s\" matches system time zone \"%s\"",
-				 win32_tzmap[i].pgtzname, tzname);
-			return win32_tzmap[i].pgtzname;
-		}
-	}
-
-	/*
-	 * Localized Windows versions return localized names for the timezone.
-	 * Scan the registry to find the English name, and then try matching
-	 * against our table again.
-	 */
-	memset(localtzname, 0, sizeof(localtzname));
-	if (RegOpenKeyEx(HKEY_LOCAL_MACHINE,
-			   "SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Time Zones",
-					 0,
-					 KEY_READ,
-					 &rootKey) != ERROR_SUCCESS)
-	{
-		ereport(LOG,
-				(errmsg("could not open registry key to identify system time zone: error code %lu",
-						GetLastError()),
-				 errdetail("The PostgreSQL time zone will be set to \"%s\".",
-						   "GMT"),
-		errhint("You can specify the correct timezone in postgresql.conf.")));
-		return NULL;			/* go to GMT */
-	}
-
-	for (idx = 0;; idx++)
-	{
-		char		keyname[256];
-		char		zonename[256];
-		DWORD		namesize;
-		FILETIME	lastwrite;
-		HKEY		key;
-		LONG		r;
-
-		memset(keyname, 0, sizeof(keyname));
-		namesize = sizeof(keyname);
-		if ((r = RegEnumKeyEx(rootKey,
-							  idx,
-							  keyname,
-							  &namesize,
-							  NULL,
-							  NULL,
-							  NULL,
-							  &lastwrite)) != ERROR_SUCCESS)
-		{
-			if (r == ERROR_NO_MORE_ITEMS)
-				break;
-			ereport(LOG,
-					(errmsg_internal("could not enumerate registry subkeys to identify system time zone: %d", (int) r)));
-			break;
-		}
-
-		if ((r = RegOpenKeyEx(rootKey, keyname, 0, KEY_READ, &key)) != ERROR_SUCCESS)
-		{
-			ereport(LOG,
-					(errmsg_internal("could not open registry subkey to identify system time zone: %d", (int) r)));
-			break;
-		}
-
-		memset(zonename, 0, sizeof(zonename));
-		namesize = sizeof(zonename);
-		if ((r = RegQueryValueEx(key, "Std", NULL, NULL, (unsigned char *) zonename, &namesize)) != ERROR_SUCCESS)
-		{
-			ereport(LOG,
-					(errmsg_internal("could not query value for key \"std\" to identify system time zone \"%s\": %d",
-									 keyname, (int) r)));
-			RegCloseKey(key);
-			continue;			/* Proceed to look at the next timezone */
-		}
-		if (strcmp(tzname, zonename) == 0)
-		{
-			/* Matched zone */
-			strcpy(localtzname, keyname);
-			RegCloseKey(key);
-			break;
-		}
-		memset(zonename, 0, sizeof(zonename));
-		namesize = sizeof(zonename);
-		if ((r = RegQueryValueEx(key, "Dlt", NULL, NULL, (unsigned char *) zonename, &namesize)) != ERROR_SUCCESS)
-		{
-			ereport(LOG,
-					(errmsg_internal("could not query value for key \"dlt\" to identify system time zone \"%s\": %d",
-									 keyname, (int) r)));
-			RegCloseKey(key);
-			continue;			/* Proceed to look at the next timezone */
-		}
-		if (strcmp(tzname, zonename) == 0)
-		{
-			/* Matched DST zone */
-			strcpy(localtzname, keyname);
-			RegCloseKey(key);
-			break;
-		}
-
-		RegCloseKey(key);
-	}
-
-	RegCloseKey(rootKey);
-
-	if (localtzname[0])
-	{
-		/* Found a localized name, so scan for that one too */
-		for (i = 0; win32_tzmap[i].stdname != NULL; i++)
-		{
-			if (strcmp(localtzname, win32_tzmap[i].stdname) == 0 ||
-				strcmp(localtzname, win32_tzmap[i].dstname) == 0)
-			{
-				elog(DEBUG4, "TZ \"%s\" matches localized system time zone \"%s\" (\"%s\")",
-					 win32_tzmap[i].pgtzname, tzname, localtzname);
-				return win32_tzmap[i].pgtzname;
-			}
-		}
-	}
-
-	ereport(LOG,
-			(errmsg("could not find a match for system time zone \"%s\"",
-					tzname),
-			 errdetail("The PostgreSQL time zone will be set to \"%s\".",
-					   "GMT"),
-	   errhint("You can specify the correct timezone in postgresql.conf.")));
-	return NULL;				/* go to GMT */
-}
-#endif   /* WIN32 */
-
-
-
 /*
  * We keep loaded timezones in a hashtable so we don't have to
  * load and parse the TZ definition file every time one is selected.
@@ -1262,8 +203,18 @@ init_timezone_hashtable(void)
 /*
  * Load a timezone from file or from cache.
  * Does not verify that the timezone is acceptable!
+ *
+ * "GMT" is always interpreted as the tzparse() definition, without attempting
+ * to load a definition from the filesystem.  This has a number of benefits:
+ * 1. It's guaranteed to succeed, so we don't have the failure mode wherein
+ * the bootstrap default timezone setting doesn't work (as could happen if
+ * the OS attempts to supply a leap-second-aware version of "GMT").
+ * 2. Because we aren't accessing the filesystem, we can safely initialize
+ * the "GMT" zone definition before my_exec_path is known.
+ * 3. It's quick enough that we don't waste much time when the bootstrap
+ * default timezone setting is later overridden from postgresql.conf.
  */
-struct pg_tz *
+pg_tz *
 pg_tzset(const char *name)
 {
 	pg_tz_cache *tzp;
@@ -1300,7 +251,20 @@ pg_tzset(const char *name)
 		return &tzp->tz;
 	}
 
-	if (tzload(uppername, canonname, &tzstate, TRUE) != 0)
+	/*
+	 * "GMT" is always sent to tzparse(), as per discussion above.
+	 */
+	if (strcmp(uppername, "GMT") == 0)
+	{
+		if (tzparse(uppername, &tzstate, TRUE) != 0)
+		{
+			/* This really, really should not happen ... */
+			elog(ERROR, "could not initialize GMT time zone");
+		}
+		/* Use uppercase name as canonical */
+		strcpy(canonname, uppername);
+	}
+	else if (tzload(uppername, canonname, &tzstate, TRUE) != 0)
 	{
 		if (uppername[0] == ':' || tzparse(uppername, &tzstate, FALSE) != 0)
 		{
@@ -1325,176 +289,27 @@ pg_tzset(const char *name)
 }
 
 
-/*
- * Check whether timezone is acceptable.
- *
- * What we are doing here is checking for leap-second-aware timekeeping.
- * We need to reject such TZ settings because they'll wreak havoc with our
- * date/time arithmetic.
- *
- * NB: this must NOT ereport(ERROR).  The caller must get control back so that
- * it can restore the old value of TZ if we don't like the new one.
- */
-bool
-tz_acceptable(pg_tz *tz)
-{
-	struct pg_tm *tt;
-	pg_time_t	time2000;
-
-	/*
-	 * To detect leap-second timekeeping, run pg_localtime for what should be
-	 * GMT midnight, 2000-01-01.  Insist that the tm_sec value be zero; any
-	 * other result has to be due to leap seconds.
-	 */
-	time2000 = (POSTGRES_EPOCH_JDATE - UNIX_EPOCH_JDATE) * SECS_PER_DAY;
-	tt = pg_localtime(&time2000, tz);
-	if (!tt || tt->tm_sec != 0)
-		return false;
-
-	return true;
-}
-
-
-/*
- * Get a pg_tz struct for the given timezone name.	Returns NULL if name
- * is invalid or not an "acceptable" zone.
- */
-static pg_tz *
-get_pg_tz_for_zone(const char *tzname)
-{
-	pg_tz	   *tz;
-
-	if (!tzname || !tzname[0])
-		return NULL;
-
-	tz = pg_tzset(tzname);
-	if (!tz)
-		return NULL;
-
-	if (!tz_acceptable(tz))
-		return NULL;
-
-	return tz;
-}
-
-/*
- * Identify a suitable default timezone setting based on the environment.
- *
- * We first look to the TZ environment variable.  If not found or not
- * recognized by our own code, we see if we can identify the timezone
- * from the behavior of the system timezone library.  When all else fails,
- * fall back to GMT.
- */
-static pg_tz *
-select_default_timezone(void)
-{
-	pg_tz	   *def_tz;
-
-	def_tz = get_pg_tz_for_zone(getenv("TZ"));
-	if (def_tz)
-		return def_tz;
-
-	def_tz = get_pg_tz_for_zone(identify_system_timezone());
-	if (def_tz)
-		return def_tz;
-
-	def_tz = get_pg_tz_for_zone("GMT");
-	if (def_tz)
-		return def_tz;
-
-	ereport(FATAL,
-			(errmsg("could not select a suitable default time zone"),
-			 errdetail("It appears that your GMT time zone uses leap seconds. PostgreSQL does not support leap seconds.")));
-	return NULL;				/* keep compiler quiet */
-}
-
-
-/*
- * Pre-initialize timezone library
- *
- * This is called before GUC variable initialization begins.  Its purpose
- * is to ensure that elog.c has a pgtz variable available to format timestamps
- * with, in case log_line_prefix is set to a value requiring that.	We cannot
- * set log_timezone yet.
- */
-void
-pg_timezone_pre_initialize(void)
-{
-	/*
-	 * We can't use tzload() because we may not know where PGSHAREDIR is (in
-	 * particular this is true in an EXEC_BACKEND subprocess). Since this
-	 * timezone variable will only be used for emergency fallback purposes, it
-	 * seems OK to just use the "lastditch" case provided by tzparse().
-	 */
-	if (tzparse("GMT", &gmt_timezone_data.state, TRUE) != 0)
-		elog(FATAL, "could not initialize GMT time zone");
-	strcpy(gmt_timezone_data.TZname, "GMT");
-	gmt_timezone = &gmt_timezone_data;
-}
-
 /*
  * Initialize timezone library
  *
- * This is called after initial loading of postgresql.conf.  If no TimeZone
- * setting was found therein, we try to derive one from the environment.
- * Likewise for log_timezone.
- *
- * Note: this is also called from ProcessConfigFile, to re-establish valid
- * GUC settings if the GUCs have been reset to default following their
- * removal from postgresql.conf.
+ * This is called before GUC variable initialization begins.  Its purpose
+ * is to ensure that log_timezone has a valid value before any logging GUC
+ * variables could become set to values that require elog.c to provide
+ * timestamps (e.g., log_line_prefix).  We may as well initialize
+ * session_timestamp to something valid, too.
  */
 void
 pg_timezone_initialize(void)
 {
-	pg_tz	   *def_tz = NULL;
-
-	/*
-	 * Make sure that session_timezone and log_timezone are set.
-	 * (session_timezone could still be NULL even if a timezone value was set
-	 * in postgresql.conf, if that setting was interval-based rather than
-	 * timezone-based.)
-	 */
-	if (!session_timezone)
-	{
-		def_tz = select_default_timezone();
-		session_timezone = def_tz;
-	}
-	if (!log_timezone)
-	{
-		/* Don't duplicate work */
-		if (!def_tz)
-			def_tz = select_default_timezone();
-		log_timezone = def_tz;
-	}
-
 	/*
-	 * Now, set the timezone and log_timezone GUCs if they're still default.
-	 * (This will redundantly call pg_tzset().)
-	 *
-	 * We choose to label these values PGC_S_ENV_VAR, rather than
-	 * PGC_S_DYNAMIC_DEFAULT which would be functionally equivalent, because
-	 * they came either from getenv("TZ") or from libc behavior that's
-	 * determined by process environment of some kind.
-	 *
-	 * Note: in the case where a setting has just been removed from
-	 * postgresql.conf, this code will not do what you might expect, namely
-	 * call select_default_timezone() and install that value as the setting.
-	 * Rather, the previously active setting --- typically the one from
-	 * postgresql.conf --- will be reinstalled, relabeled as PGC_S_ENV_VAR. If
-	 * we did try to install the "correct" default value, the effect would be
-	 * that each postmaster child would independently run an extremely
-	 * expensive search of the timezone database, bringing the database to its
-	 * knees for possibly multiple seconds.  This is so unpleasant, and could
-	 * so easily be triggered quite unintentionally, that it seems better to
-	 * violate the principle of least astonishment.
+	 * We may not yet know where PGSHAREDIR is (in particular this is true in
+	 * an EXEC_BACKEND subprocess).  So use "GMT", which pg_tzset forces to
+	 * be interpreted without reference to the filesystem.  This corresponds
+	 * to the bootstrap default for these variables in guc.c, although in
+	 * principle it could be different.
 	 */
-	if (GetConfigOptionResetString("timezone") == NULL)
-		SetConfigOption("timezone", pg_get_timezone_name(session_timezone),
-						PGC_POSTMASTER, PGC_S_ENV_VAR);
-
-	if (GetConfigOptionResetString("log_timezone") == NULL)
-		SetConfigOption("log_timezone", pg_get_timezone_name(log_timezone),
-						PGC_POSTMASTER, PGC_S_ENV_VAR);
+	session_timezone = pg_tzset("GMT");
+	log_timezone = session_timezone;
 }
 
 
@@ -1608,7 +423,7 @@ pg_tzenumerate_next(pg_tzenum *dir)
 			continue;
 		}
 
-		if (!tz_acceptable(&dir->tz))
+		if (!pg_tz_acceptable(&dir->tz))
 		{
 			/* Ignore leap-second zones */
 			continue;
-- 
GitLab