Make timetz_zone() stable, and correct a bug for DYNTZ abbreviations.

Historically, timetz_zone() has used time(NULL) as the reference point
for deciding whether DST is active.  That means its result can change
intra-statement, requiring it to be marked VOLATILE (cf. 35979e6c3).
But that definition is pretty inconsistent with the way we deal with
timestamps elsewhere.  Let's make it use the transaction start time
("now()") as the reference point instead.  That lets it be marked
STABLE, and also saves a kernel call per invocation.

While at it, remove the function's use of pg_time_t and pg_localtime.
Those are inconsistent with the other code in this area, which indeed
created a bug: timetz_zone() delivered completely wrong answers if
the zone was specified by a dynamic TZ abbreviation.  (We need to do
something about that in the back branches, but the fix will look
different from this.)

Aleksander Alekseev and Tom Lane

Discussion: https://postgr.es/m/CAJ7c6TOMG8zSNEZtCn5SPe+cCk3Lfxb71ZaQwT2F4T7PJ_t=KA@mail.gmail.com

diff --git a/src/backend/utils/adt/date.c b/src/backend/utils/adt/date.c
index 0bea16cb671ac90461627ed11ef7441c56bd32a9..9e8baeaa9c8b909599553bfd320bb21b486f6426 100644 (file)
--- a/src/backend/utils/adt/date.c
+++ b/src/backend/utils/adt/date.c
@@ -1481,9 +1481,7 @@ float_time_overflows(int hour, int min, double sec)
 /* time2tm()
  * Convert time data type to POSIX time structure.
  *
- * For dates within the range of pg_time_t, convert to the local time zone.
- * If out of this range, leave as UTC (in practice that could only happen
- * if pg_time_t is just 32 bits) - thomas 97/05/27
+ * Note that only the hour/min/sec/fractional-sec fields are filled in.
  */
 int
 time2tm(TimeADT time, struct pg_tm *tm, fsec_t *fsec)
@@ -3029,7 +3027,7 @@ extract_timetz(PG_FUNCTION_ARGS)
 
 /* timetz_zone()
  * Encode time with time zone type with specified time zone.
- * Applies DST rules as of the current date.
+ * Applies DST rules as of the transaction start time.
  */
 Datum
 timetz_zone(PG_FUNCTION_ARGS)
@@ -3068,12 +3066,11 @@ timetz_zone(PG_FUNCTION_ARGS)
    }
    else if (type == DYNTZ)
    {
-       /* dynamic-offset abbreviation, resolve using current time */
-       pg_time_t   now = (pg_time_t) time(NULL);
-       struct pg_tm *tm;
+       /* dynamic-offset abbreviation, resolve using transaction start time */
+       TimestampTz now = GetCurrentTransactionStartTimestamp();
+       int         isdst;
 
-       tm = pg_localtime(&now, tzp);
-       tz = DetermineTimeZoneAbbrevOffset(tm, tzname, tzp);
+       tz = DetermineTimeZoneAbbrevOffsetTS(now, tzname, tzp, &isdst);
    }
    else
    {
@@ -3081,12 +3078,15 @@ timetz_zone(PG_FUNCTION_ARGS)
        tzp = pg_tzset(tzname);
        if (tzp)
        {
-           /* Get the offset-from-GMT that is valid today for the zone */
-           pg_time_t   now = (pg_time_t) time(NULL);
-           struct pg_tm *tm;
+           /* Get the offset-from-GMT that is valid now for the zone */
+           TimestampTz now = GetCurrentTransactionStartTimestamp();
+           struct pg_tm tm;
+           fsec_t      fsec;
 
-           tm = pg_localtime(&now, tzp);
-           tz = -tm->tm_gmtoff;
+           if (timestamp2tm(now, &tz, &tm, &fsec, NULL, tzp) != 0)
+               ereport(ERROR,
+                       (errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
+                        errmsg("timestamp out of range")));
        }
        else
        {

diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
index 3190d82a868d1485c947e5212d378c419a40bac0..fb35d3d5be43fcd8fa0d5e29411b9edd162aceb9 100644 (file)
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@@ -53,6 +53,6 @@
  */
 
 /*                         yyyymmddN */
-#define CATALOG_VERSION_NO 202109032
+#define CATALOG_VERSION_NO 202109061
 
 #endif

diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index c07b2c6a556a1e96c65ca5379dbf799d0b2bc378..d068d6532ecfd357e3d4c39de83c6293e8712966 100644 (file)
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5953,7 +5953,7 @@
   proname => 'timestamp_larger', prorettype => 'timestamp',
   proargtypes => 'timestamp timestamp', prosrc => 'timestamp_larger' },
 { oid => '2037', descr => 'adjust time with time zone to new zone',
-  proname => 'timezone', provolatile => 'v', prorettype => 'timetz',
+  proname => 'timezone', provolatile => 's', prorettype => 'timetz',
   proargtypes => 'text timetz', prosrc => 'timetz_zone' },
 { oid => '2038', descr => 'adjust time with time zone to new zone',
   proname => 'timezone', prorettype => 'timetz',