Support timezone abbreviations that sometimes change.

Up to now, PG has assumed that any given timezone abbreviation (such as
"EDT") represents a constant GMT offset in the usage of any particular
region; we had a way to configure what that offset was, but not for it
to be changeable over time.  But, as with most things horological, this
view of the world is too simplistic: there are numerous regions that have
at one time or another switched to a different GMT offset but kept using
the same timezone abbreviation.  Almost the entire Russian Federation did
that a few years ago, and later this month they're going to do it again.
And there are similar examples all over the world.

To cope with this, invent the notion of a "dynamic timezone abbreviation",
which is one that is referenced to a particular underlying timezone
(as defined in the IANA timezone database) and means whatever it currently
means in that zone.  For zones that use or have used daylight-savings time,
the standard and DST abbreviations continue to have the property that you
can specify standard or DST time and get that time offset whether or not
DST was theoretically in effect at the time.  However, the abbreviations
mean what they meant at the time in question (or most recently before that
time) rather than being absolutely fixed.

The standard abbreviation-list files have been changed to use this behavior
for abbreviations that have actually varied in meaning since 1970.  The
old simple-numeric definitions are kept for abbreviations that have not
changed, since they are a bit faster to resolve.

While this is clearly a new feature, it seems necessary to back-patch it
into all active branches, because otherwise use of Russian zone
abbreviations is going to become even more problematic than it already was.
This change supersedes the changes in commit 513d06ded et al to modify the
fixed meanings of the Russian abbreviations; since we've not shipped that
yet, this will avoid an undesirably incompatible (not to mention incorrect)
change in behavior for timestamps between 2011 and 2014.

This patch makes some cosmetic changes in ecpglib to keep its usage of
datetime lookup tables as similar as possible to the backend code, but
doesn't do anything about the increasingly obsolete set of timezone
abbreviation definitions that are hard-wired into ecpglib.  Whatever we
do about that will likely not be appropriate material for back-patching.
Also, a potential free() of a garbage pointer after an out-of-memory
failure in ecpglib has been fixed.

This patch also fixes pre-existing bugs in DetermineTimeZoneOffset() that
caused it to produce unexpected results near a timezone transition, if
both the "before" and "after" states are marked as standard time.  We'd
only ever thought about or tested transitions between standard and DST
time, but that's not what's happening when a zone simply redefines their
base GMT offset.

In passing, update the SGML documentation to refer to the Olson/zoneinfo/
zic timezone database as the "IANA" database, since it's now being
maintained under the auspices of IANA.

13 files changed, 250 insertions, 133 deletions

diff --git a/src/timezone/known_abbrevs.txt b/src/timezone/known_abbrevs.txt
index f309a48066b..db78cf3492b 100644
--- a/src/timezone/known_abbrevs.txt
+++ b/src/timezone/known_abbrevs.txt
@@ -85,6 +85,7 @@ IDT	10800	D
 IOT	21600
 IRDT	16200	D
 IRKT	28800
+IRKT	32400
 IRST	12600
 IST	19800
 IST	3600	D
@@ -93,11 +94,13 @@ JST	32400
 KGT	21600
 KOST	39600
 KRAT	25200
+KRAT	28800
 KST	32400
 LHDT	39600	D
 LHST	37800
 LINT	50400
 MAGT	36000
+MAGT	43200
 MART	-34200
 MAWT	18000
 MDT	-21600	D
@@ -107,6 +110,7 @@ MHT	43200
 MIST	39600
 MMT	23400
 MSK	10800
+MSK	14400
 MST	-25200
 MUT	14400
 MVT	18000
@@ -115,6 +119,7 @@ NCT	39600
 NDT	-9000	D
 NFT	41400
 NOVT	21600
+NOVT	25200
 NPT	20700
 NRT	43200
 NST	-12600
@@ -122,6 +127,7 @@ NUT	-39600
 NZDT	46800	D
 NZST	43200
 OMST	21600
+OMST	25200
 ORAT	18000
 PDT	-25200	D
 PET	-18000
@@ -141,6 +147,7 @@ QYZT	21600
 RET	14400
 ROTT	-10800
 SAKT	36000
+SAKT	39600
 SAMT	14400
 SAST	7200
 SBT	39600
@@ -165,6 +172,7 @@ UYT	-10800
 UZT	18000
 VET	-16200
 VLAT	36000
+VLAT	39600
 VOST	21600
 VUT	39600
 WAKT	43200
@@ -182,4 +190,6 @@ WSDT	50400	D
 WSST	46800
 XJT	21600
 YAKT	32400
+YAKT	36000
 YEKT	18000
+YEKT	21600
diff --git a/src/timezone/localtime.c b/src/timezone/localtime.c
index 85b227c9255..19a24e1d960 100644
--- a/src/timezone/localtime.c
+++ b/src/timezone/localtime.c
@@ -1292,9 +1292,9 @@ increment_overflow(int *number, int delta)
 }
 
 /*
- * Find the next DST transition time after the given time
+ * Find the next DST transition time in the given zone after the given time
  *
- * *timep is the input value, the other parameters are output values.
+ * *timep and *tz are input arguments, the other parameters are output values.
  *
  * When the function result is 1, *boundary is set to the time_t
  * representation of the next DST transition time after *timep,
@@ -1445,6 +1445,110 @@ pg_next_dst_boundary(const pg_time_t *timep,
 }
 
 /*
+ * Identify a timezone abbreviation's meaning in the given zone
+ *
+ * Determine the GMT offset and DST flag associated with the abbreviation.
+ * This is generally used only when the abbreviation has actually changed
+ * meaning over time; therefore, we also take a UTC cutoff time, and return
+ * the meaning in use at or most recently before that time, or the meaning
+ * in first use after that time if the abbrev was never used before that.
+ *
+ * On success, returns TRUE and sets *gmtoff and *isdst.  If the abbreviation
+ * was never used at all in this zone, returns FALSE.
+ *
+ * Note: abbrev is matched case-sensitively; it should be all-upper-case.
+ */
+bool
+pg_interpret_timezone_abbrev(const char *abbrev,
+							 const pg_time_t *timep,
+							 long int *gmtoff,
+							 int *isdst,
+							 const pg_tz *tz)
+{
+	const struct state *sp;
+	const char *abbrs;
+	const struct ttinfo *ttisp;
+	int			abbrind;
+	int			cutoff;
+	int			i;
+	const pg_time_t t = *timep;
+
+	sp = &tz->state;
+
+	/*
+	 * Locate the abbreviation in the zone's abbreviation list.  We assume
+	 * there are not duplicates in the list.
+	 */
+	abbrs = sp->chars;
+	abbrind = 0;
+	while (abbrind < sp->charcnt)
+	{
+		if (strcmp(abbrev, abbrs + abbrind) == 0)
+			break;
+		while (abbrs[abbrind] != '\0')
+			abbrind++;
+		abbrind++;
+	}
+	if (abbrind >= sp->charcnt)
+		return FALSE;			/* not there! */
+
+	/*
+	 * Unlike pg_next_dst_boundary, we needn't sweat about extrapolation
+	 * (goback/goahead zones).  Finding the newest or oldest meaning of the
+	 * abbreviation should get us what we want, since extrapolation would just
+	 * be repeating the newest or oldest meanings.
+	 *
+	 * Use binary search to locate the first transition > cutoff time.
+	 */
+	{
+		int			lo = 0;
+		int			hi = sp->timecnt;
+
+		while (lo < hi)
+		{
+			int			mid = (lo + hi) >> 1;
+
+			if (t < sp->ats[mid])
+				hi = mid;
+			else
+				lo = mid + 1;
+		}
+		cutoff = lo;
+	}
+
+	/*
+	 * Scan backwards to find the latest interval using the given abbrev
+	 * before the cutoff time.
+	 */
+	for (i = cutoff - 1; i >= 0; i--)
+	{
+		ttisp = &sp->ttis[sp->types[i]];
+		if (ttisp->tt_abbrind == abbrind)
+		{
+			*gmtoff = ttisp->tt_gmtoff;
+			*isdst = ttisp->tt_isdst;
+			return TRUE;
+		}
+	}
+
+	/*
+	 * Not there, so scan forwards to find the first one after.
+	 */
+	for (i = cutoff; i < sp->timecnt; i++)
+	{
+		ttisp = &sp->ttis[sp->types[i]];
+		if (ttisp->tt_abbrind == abbrind)
+		{
+			*gmtoff = ttisp->tt_gmtoff;
+			*isdst = ttisp->tt_isdst;
+			return TRUE;
+		}
+	}
+
+	return FALSE;				/* hm, not actually used in any interval? */
+}
+
+/*
  * If the given timezone uses only one GMT offset, store that offset
  * into *gmtoff and return TRUE, else return FALSE.
  */
diff --git a/src/timezone/tznames/America.txt b/src/timezone/tznames/America.txt
index 54b51fe0054..9e6273207c1 100644
--- a/src/timezone/tznames/America.txt
+++ b/src/timezone/tznames/America.txt
@@ -47,7 +47,7 @@ AMT    -14400    # Amazon Time
                  #     (America/Cuiaba)
                  #     (America/Manaus)
                  #     (America/Porto_Velho)
-ART    -10800    # Argentina Time
+ART    America/Argentina/Buenos_Aires  # Argentina Time
                  #     (America/Argentina/Buenos_Aires)
                  #     (America/Argentina/Cordoba)
                  #     (America/Argentina/Tucuman)
@@ -58,7 +58,7 @@ ART    -10800    # Argentina Time
                  #     (America/Argentina/Mendoza)
                  #     (America/Argentina/Rio_Gallegos)
                  #     (America/Argentina/Ushuaia)
-ARST    -7200 D  # Argentina Summer Time
+ARST    America/Argentina/Buenos_Aires  # Argentina Summer Time
 # CONFLICT! AST is not unique
 # Other timezones:
 #  - AST: Arabic Standard Time (Asia)
@@ -228,7 +228,7 @@ GMT         0    # Greenwich Mean Time
                  #     (Etc/GMT)
                  #     (Europe/Dublin)
                  #     (Europe/London)
-GYT    -14400    # Guyana Time
+GYT    America/Guyana  # Guyana Time
                  #     (America/Guyana)
 HADT   -32400 D  # Hawaii-Aleutian Daylight Time
                  #     (America/Adak)
@@ -285,15 +285,15 @@ PST    -28800    # Pacific Standard Time
                  #     (Pacific/Pitcairn)
 PYST   -10800 D  # Paraguay Summer Time
                  #     (America/Asuncion)
-PYT    -14400    # Paraguay Time
+PYT    America/Asuncion  # Paraguay Time
                  #     (America/Asuncion)
-SRT    -10800    # Suriname Time
+SRT    America/Paramaribo  # Suriname Time
                  #     (America/Paramaribo)
 UYST    -7200 D  # Uruguay Summer Time
                  #     (America/Montevideo)
 UYT    -10800    # Uruguay Time
                  #     (America/Montevideo)
-VET    -16200    # Venezuela Time (caution: this used to mean -14400)
+VET    America/Caracas  # Venezuela Time
                  #     (America/Caracas)
 WGST    -7200 D  # Western Greenland Summer Time
                  #     (America/Godthab)
diff --git a/src/timezone/tznames/Antarctica.txt b/src/timezone/tznames/Antarctica.txt
index 5a032506526..2359020ef87 100644
--- a/src/timezone/tznames/Antarctica.txt
+++ b/src/timezone/tznames/Antarctica.txt
@@ -16,11 +16,11 @@ CLST   -10800 D  # Chile Summer Time
 CLT    -14400    # Chile Time
                  #     (America/Santiago)
                  #     (Antarctica/Palmer)
-DAVT    25200    # Davis Time (Antarctica)
+DAVT    Antarctica/Davis  # Davis Time (Antarctica)
                  #     (Antarctica/Davis)
 DDUT    36000    # Dumont-d`Urville Time (Antarctica)
                  #     (Antarctica/DumontDUrville)
-MAWT    18000    # Mawson Time (Antarctica) (caution: this used to mean 21600)
+MAWT    Antarctica/Mawson  # Mawson Time (Antarctica)
                  #     (Antarctica/Mawson)
 MIST    39600    # Macquarie Island Time
                  #     (Antarctica/Macquarie)
diff --git a/src/timezone/tznames/Asia.txt b/src/timezone/tznames/Asia.txt
index 8c3cb354713..bb286464297 100644
--- a/src/timezone/tznames/Asia.txt
+++ b/src/timezone/tznames/Asia.txt
@@ -15,17 +15,19 @@ ALMT    21600    # Alma-Ata Time
 # CONFLICT! AMST is not unique
 # Other timezones:
 #  - AMST: Amazon Summer Time (America)
-AMST    18000 D  # Armenia Summer Time
+AMST    Asia/Yerevan  # Armenia Summer Time
                  #     (Asia/Yerevan)
 # CONFLICT! AMT is not unique
 # Other timezones:
 #  - AMT: Amazon Time (America)
-AMT     14400    # Armenia Time
+AMT     Asia/Yerevan  # Armenia Time
                  #     (Asia/Yerevan)
-ANAST   46800 D  # Anadyr Summer Time (obsolete)
-ANAT    43200    # Anadyr Time
+ANAST   Asia/Anadyr  # Anadyr Summer Time (obsolete)
+ANAT    Asia/Anadyr  # Anadyr Time
                  #     (Asia/Anadyr)
-AQTT    18000    # Aqtau Time (obsolete)
+AQTST   Asia/Aqtau  # Aqtau Summer Time (obsolete)
+AQTT    Asia/Aqtau  # Aqtau Time
+                 #     (Asia/Aqtau)
 # CONFLICT! AST is not unique
 # Other timezones:
 #  - AST: Atlantic Standard Time (America)
@@ -41,9 +43,9 @@ AST     10800    # Arabia Standard Time
                  #     (Asia/Kuwait)
                  #     (Asia/Qatar)
                  #     (Asia/Riyadh)
-AZST    18000 D  # Azerbaijan Summer Time
+AZST    Asia/Baku  # Azerbaijan Summer Time
                  #     (Asia/Baku)
-AZT     14400    # Azerbaijan Time
+AZT     Asia/Baku  # Azerbaijan Time
                  #     (Asia/Baku)
 BDT     21600    # Bangladesh Time
                  #     (Asia/Dhaka)
@@ -54,7 +56,7 @@ BTT     21600    # Bhutan Time
                  #     (Asia/Thimphu)
 CCT     28800    # China Coastal Time (not in zic)
 CHOST   36000 D  # Choibalsan Summer Time (obsolete)
-CHOT    28800    # Choibalsan Time (caution: this used to mean 32400)
+CHOT    Asia/Choibalsan  # Choibalsan Time
                  #     (Asia/Choibalsan)
 CIT     28800    # Central Indonesia Time (obsolete, WITA is now preferred)
 EEST    10800 D  # East-Egypt Summer Time
@@ -105,9 +107,8 @@ EET      7200    # East-Egypt Time
                  #     (Europe/Vilnius)
                  #     (Europe/Zaporozhye)
 EIT     32400    # East Indonesia Time (obsolete, WIT is now preferred)
-GEST    14400 D  # Georgia Summer Time (obsolete)
-                 #     (Asia/Tbilisi)
-GET     14400    # Georgia Time (caution: this used to mean 10800)
+GEST    Asia/Tbilisi  # Georgia Summer Time (obsolete)
+GET     Asia/Tbilisi  # Georgia Time
                  #     (Asia/Tbilisi)
 # CONFLICT! GST is not unique
 # Other timezones:
@@ -117,7 +118,7 @@ GST     14400    # Gulf Standard Time
                  #     (Asia/Muscat)
 HKT     28800    # Hong Kong Time (not in zic)
 HOVST   28800 D  # Hovd Summer Time (obsolete)
-HOVT    25200    # Hovd Time
+HOVT    Asia/Hovd  # Hovd Time
                  #     (Asia/Hovd)
 ICT     25200    # Indochina Time
                  #     (Asia/Bangkok)
@@ -126,12 +127,12 @@ ICT     25200    # Indochina Time
                  #     (Asia/Vientiane)
 IDT     10800 D  # Israel Daylight Time
                  #     (Asia/Jerusalem)
-IRDT    16200 D  # Iran Daylight Time
+IRDT    Asia/Tehran  # Iran Daylight Time
                  #     (Asia/Tehran)
-IRKST   32400 D  # Irkutsk Summer Time (obsolete)
-IRKT    28800    # Irkutsk Time (caution: this used to mean 32400)
+IRKST   Asia/Irkutsk  # Irkutsk Summer Time (obsolete)
+IRKT    Asia/Irkutsk  # Irkutsk Time
                  #     (Asia/Irkutsk)
-IRST    12600    # Iran Standard Time
+IRST    Asia/Tehran  # Iran Standard Time
                  #     (Asia/Tehran)
 IRT     12600    # Iran Time (not in zic)
 # CONFLICT! IST is not unique
@@ -151,35 +152,34 @@ JST     32400    # Japan Standard Time
                  #     (Asia/Tokyo)
 KDT     36000 D  # Korean Daylight Time (not in zic)
 KGST    21600 D  # Kyrgyzstan Summer Time (obsolete)
+KGT     Asia/Bishkek  # Kyrgyzstan Time
                  #     (Asia/Bishkek)
-KGT     21600    # Kyrgyzstan Time (caution: this used to mean 18000)
-                 #     (Asia/Bishkek)
-KRAST   28800 D  # Krasnoyarsk Summer Time (obsolete)
-KRAT    25200    # Krasnoyarsk Time (caution: this used to mean 28800)
+KRAST   Asia/Krasnoyarsk  # Krasnoyarsk Summer Time (obsolete)
+KRAT    Asia/Krasnoyarsk  # Krasnoyarsk Time
                  #     (Asia/Krasnoyarsk)
 KST     32400    # Korean Standard Time
                  #     (Asia/Pyongyang)
-LKT     21600    # Lanka Time (obsolete)
-MAGST   43200 D  # Magadan Summer Time (obsolete)
-MAGT    36000    # Magadan Time (caution: this used to mean 43200)
+LKT     Asia/Colombo  # Lanka Time (obsolete)
+MAGST   Asia/Magadan  # Magadan Summer Time (obsolete)
+MAGT    Asia/Magadan  # Magadan Time
                  #     (Asia/Magadan)
 MMT     23400    # Myanmar Time
                  #     (Asia/Rangoon)
 MYT     28800    # Malaysia Time
                  #     (Asia/Kuala_Lumpur)
                  #     (Asia/Kuching)
-NOVST   25200 D  # Novosibirsk Summer Time (obsolete)
-NOVT    21600    # Novosibirsk Time (caution: this used to mean 25200)
+NOVST   Asia/Novosibirsk  # Novosibirsk Summer Time (obsolete)
+NOVT    Asia/Novosibirsk  # Novosibirsk Time
                  #     (Asia/Novosibirsk)
 NPT     20700    # Nepal Time
                  #     (Asia/Katmandu)
-OMSST   25200 D  # Omsk Summer Time (obsolete)
-OMST    21600    # Omsk Time (caution: this used to mean 25200)
+OMSST   Asia/Omsk  # Omsk Summer Time (obsolete)
+OMST    Asia/Omsk  # Omsk Time
                  #     (Asia/Omsk)
-ORAT    18000    # Oral Time
+ORAT    Asia/Oral  # Oral Time
                  #     (Asia/Oral)
-PETST   46800 D  # Petropavlovsk-Kamchatski Summer Time (obsolete)
-PETT    43200    # Petropavlovsk-Kamchatski Time
+PETST   Asia/Kamchatka  # Petropavlovsk-Kamchatski Summer Time (obsolete)
+PETT    Asia/Kamchatka  # Petropavlovsk-Kamchatski Time
                  #     (Asia/Kamchatka)
 PHT     28800    # Philippine Time
                  #     (Asia/Manila)
@@ -189,10 +189,10 @@ PKST    21600 D  # Pakistan Summer Time
                  #     (Asia/Karachi)
 QYZT    21600    # Kizilorda Time
                  #     (Asia/Qyzylorda)
-SAKST   39600 D  # Sakhalin Summer Time (obsolete)
-SAKT    36000    # Sakhalin Time (caution: this used to mean 39600)
+SAKST   Asia/Sakhalin  # Sakhalin Summer Time (obsolete)
+SAKT    Asia/Sakhalin  # Sakhalin Time
                  #     (Asia/Sakhalin)
-SGT     28800    # Singapore Time
+SGT     Asia/Singapore  # Singapore Time
                  #     (Asia/Singapore)
 SRET    39600    # Srednekolymsk Time
                  #     (Asia/Srednekolymsk)
@@ -200,10 +200,10 @@ TJT     18000    # Tajikistan Time
                  #     (Asia/Dushanbe)
 TLT     32400    # East Timor Time
                  #     (Asia/Dili)
-TMT     18000    # Turkmenistan Time
+TMT     Asia/Ashgabat  # Turkmenistan Time
                  #     (Asia/Ashgabat)
 ULAST   32400 D  # Ulan Bator Summer Time (obsolete)
-ULAT    28800    # Ulan Bator Time
+ULAT    Asia/Ulaanbaatar  # Ulan Bator Time
                  #     (Asia/Ulaanbaatar)
 UZST    21600 D  # Uzbekistan Summer Time
                  #     (Asia/Samarkand)
@@ -211,8 +211,8 @@ UZST    21600 D  # Uzbekistan Summer Time
 UZT     18000    # Uzbekistan Time
                  #     (Asia/Samarkand)
                  #     (Asia/Tashkent)
-VLAST   39600 D  # Vladivostok Summer Time (obsolete)
-VLAT    36000    # Vladivostok Time (caution: this used to mean 39600)
+VLAST   Asia/Vladivostok  # Vladivostok Summer Time (obsolete)
+VLAT    Asia/Vladivostok  # Vladivostok Time
                  #     (Asia/Vladivostok)
 WIB     25200    # Waktu Indonesia Barat
                  #     (Asia/Jakarta)
@@ -223,9 +223,9 @@ WITA    28800    # Waktu Indonesia Tengah
                  #     (Asia/Makassar)
 XJT     21600    # Xinjiang Time
                  #     (Asia/Urumqi)
-YAKST   36000 D  # Yakutsk Summer Time (obsolete)
-YAKT    32400    # Yakutsk Time (caution: this used to mean 36000)
+YAKST   Asia/Yakutsk  # Yakutsk Summer Time (obsolete)
+YAKT    Asia/Yakutsk  # Yakutsk Time
                  #     (Asia/Yakutsk)
 YEKST   21600 D  # Yekaterinburg Summer Time (obsolete)
-YEKT    18000    # Yekaterinburg Time (caution: this used to mean 21600)
+YEKT    Asia/Yekaterinburg  # Yekaterinburg Time
                  #     (Asia/Yekaterinburg)
diff --git a/src/timezone/tznames/Atlantic.txt b/src/timezone/tznames/Atlantic.txt
index c65734b0aee..1d34d1ed4be 100644
--- a/src/timezone/tznames/Atlantic.txt
+++ b/src/timezone/tznames/Atlantic.txt
@@ -48,11 +48,11 @@ AZOST       0 D  # Azores Summer Time
                  #     (Atlantic/Azores)
 AZOT    -3600    # Azores Time
                  #     (Atlantic/Azores)
-CVT     -3600    # Cape Verde Time
+CVT     Atlantic/Cape_Verde  # Cape Verde Time
                  #     (Atlantic/Cape_Verde)
-FKST   -10800    # Falkland Islands Summer Time (now used all year round)
+FKST    Atlantic/Stanley  # Falkland Islands Summer/Standard Time
                  #     (Atlantic/Stanley)
-FKT    -14400    # Falkland Islands Time (obsolete)
+FKT     Atlantic/Stanley  # Falkland Islands Time (obsolete)
 GMT         0    # Greenwich Mean Time
                  #     (Africa/Abidjan)
                  #     (Africa/Bamako)
diff --git a/src/timezone/tznames/Australia.txt b/src/timezone/tznames/Australia.txt
index 837309326d3..92c296840f9 100644
--- a/src/timezone/tznames/Australia.txt
+++ b/src/timezone/tznames/Australia.txt
@@ -52,7 +52,7 @@ EAST    36000    # East Australian Standard Time (not in zic)
 # Other timezones:
 #  - EST: Eastern Standard Time (America)
 EST     36000    # Eastern Standard Time (not in zic)
-LHDT    39600 D  # Lord Howe Daylight Time
+LHDT    Australia/Lord_Howe  # Lord Howe Daylight Time
                  #     (Australia/Lord_Howe)
 LHST    37800    # Lord Howe Standard Time
                  #     (Australia/Lord_Howe)
diff --git a/src/timezone/tznames/Default b/src/timezone/tznames/Default
index 9e5209e779b..a8b8eac5182 100644
--- a/src/timezone/tznames/Default
+++ b/src/timezone/tznames/Default
@@ -54,7 +54,7 @@ AKST   -32400    # Alaska Standard Time
                  #     (America/Juneau)
                  #     (America/Nome)
                  #     (America/Yakutat)
-ART    -10800    # Argentina Time
+ART    America/Argentina/Buenos_Aires  # Argentina Time
                  #     (America/Argentina/Buenos_Aires)
                  #     (America/Argentina/Cordoba)
                  #     (America/Argentina/Tucuman)
@@ -65,7 +65,7 @@ ART    -10800    # Argentina Time
                  #     (America/Argentina/Mendoza)
                  #     (America/Argentina/Rio_Gallegos)
                  #     (America/Argentina/Ushuaia)
-ARST    -7200 D  # Argentina Summer Time
+ARST    America/Argentina/Buenos_Aires  # Argentina Summer Time
 BOT    -14400    # Bolivia Time
                  #     (America/La_Paz)
 BRA    -10800    # Brazil Time (not in zic)
@@ -170,7 +170,7 @@ FNST    -3600 D  # Fernando de Noronha Summer Time (not in zic)
                  #     (America/Noronha)
 GFT    -10800    # French Guiana Time
                  #     (America/Cayenne)
-GYT    -14400    # Guyana Time
+GYT    America/Guyana  # Guyana Time
                  #     (America/Guyana)
 MDT    -21600 D  # Mexico Mountain Daylight Time
                  # Mountain Daylight Time
@@ -219,13 +219,13 @@ PST    -28800    # Pacific Standard Time
                  #     (Pacific/Pitcairn)
 PYST   -10800 D  # Paraguay Summer Time
                  #     (America/Asuncion)
-PYT    -14400    # Paraguay Time
+PYT    America/Asuncion  # Paraguay Time
                  #     (America/Asuncion)
 UYST    -7200 D  # Uruguay Summer Time
                  #     (America/Montevideo)
 UYT    -10800    # Uruguay Time
                  #     (America/Montevideo)
-VET    -16200    # Venezuela Time (caution: this used to mean -14400)
+VET    America/Caracas  # Venezuela Time
                  #     (America/Caracas)
 WGST    -7200 D  # Western Greenland Summer Time
                  #     (America/Godthab)
@@ -234,13 +234,13 @@ WGT    -10800    # West Greenland Time
 
 #################### ANTARCTICA ####################
 
-DAVT    25200    # Davis Time (Antarctica)
+DAVT    Antarctica/Davis  # Davis Time (Antarctica)
                  #     (Antarctica/Davis)
 DDUT    36000    # Dumont-d'Urville Time (Antarctica)
                  #     (Antarctica/DumontDUrville)
                  #     (Antarctica/Palmer)
                  #     (America/Santiago)
-MAWT    18000    # Mawson Time (Antarctica) (caution: this used to mean 21600)
+MAWT    Antarctica/Mawson  # Mawson Time (Antarctica)
                  #     (Antarctica/Mawson)
 
 #################### ASIA ####################
@@ -253,19 +253,19 @@ ALMST   25200 D  # Alma-Ata Summer Time (obsolete)
 # CONFLICT! AMST is not unique
 # Other timezones:
 #  - AMST: Amazon Summer Time (America)
-AMST    18000 D  # Armenia Summer Time
+AMST    Asia/Yerevan  # Armenia Summer Time
                  #     (Asia/Yerevan)
 # CONFLICT! AMT is not unique
 # Other timezones:
 #  - AMT: Amazon Time (America)
-AMT     14400    # Armenia Time
+AMT     Asia/Yerevan  # Armenia Time
                  #     (Asia/Yerevan)
-ANAST   46800 D  # Anadyr Summer Time (obsolete)
-ANAT    43200    # Anadyr Time
+ANAST   Asia/Anadyr  # Anadyr Summer Time (obsolete)
+ANAT    Asia/Anadyr  # Anadyr Time
                  #     (Asia/Anadyr)
-AZST    18000 D  # Azerbaijan Summer Time
+AZST    Asia/Baku  # Azerbaijan Summer Time
                  #     (Asia/Baku)
-AZT     14400    # Azerbaijan Time
+AZT     Asia/Baku  # Azerbaijan Time
                  #     (Asia/Baku)
 BDT     21600    # Bangladesh Time
                  #     (Asia/Dhaka)
@@ -275,9 +275,8 @@ BORT    28800    # Borneo Time (Indonesia) (not in zic)
 BTT     21600    # Bhutan Time
                  #     (Asia/Thimphu)
 CCT     28800    # China Coastal Time (not in zic)
-GEST    14400 D  # Georgia Summer Time (obsolete)
-                 #     (Asia/Tbilisi)
-GET     14400    # Georgia Time (caution: this used to mean 10800)
+GEST    Asia/Tbilisi  # Georgia Summer Time (obsolete)
+GET     Asia/Tbilisi  # Georgia Time
                  #     (Asia/Tbilisi)
 HKT     28800    # Hong Kong Time (not in zic)
 ICT     25200    # Indochina Time
@@ -287,8 +286,8 @@ ICT     25200    # Indochina Time
                  #     (Asia/Vientiane)
 IDT     10800 D  # Israel Daylight Time
                  #     (Asia/Jerusalem)
-IRKST   32400 D  # Irkutsk Summer Time (obsolete)
-IRKT    28800    # Irkutsk Time (caution: this used to mean 32400)
+IRKST   Asia/Irkutsk  # Irkutsk Summer Time (obsolete)
+IRKT    Asia/Irkutsk  # Irkutsk Time
                  #     (Asia/Irkutsk)
 IRT     12600    # Iran Time (not in zic)
 # CONFLICT! IST is not unique
@@ -302,33 +301,32 @@ JST     32400    # Japan Standard Time
                  #     (Asia/Tokyo)
 KDT     36000 D  # Korean Daylight Time (not in zic)
 KGST    21600 D  # Kyrgyzstan Summer Time (obsolete)
+KGT     Asia/Bishkek  # Kyrgyzstan Time
                  #     (Asia/Bishkek)
-KGT     21600    # Kyrgyzstan Time (caution: this used to mean 18000)
-                 #     (Asia/Bishkek)
-KRAST   28800 D  # Krasnoyarsk Summer Time (obsolete)
-KRAT    25200    # Krasnoyarsk Time (caution: this used to mean 28800)
+KRAST   Asia/Krasnoyarsk  # Krasnoyarsk Summer Time (obsolete)
+KRAT    Asia/Krasnoyarsk  # Krasnoyarsk Time
                  #     (Asia/Krasnoyarsk)
 KST     32400    # Korean Standard Time
                  #     (Asia/Pyongyang)
-LKT     21600    # Lanka Time (obsolete)
-MAGST   43200 D  # Magadan Summer Time (obsolete)
-MAGT    36000    # Magadan Time (caution: this used to mean 43200)
+LKT     Asia/Colombo  # Lanka Time (obsolete)
+MAGST   Asia/Magadan  # Magadan Summer Time (obsolete)
+MAGT    Asia/Magadan  # Magadan Time
                  #     (Asia/Magadan)
 MMT     23400    # Myanmar Time
                  #     (Asia/Rangoon)
 MYT     28800    # Malaysia Time
                  #     (Asia/Kuala_Lumpur)
                  #     (Asia/Kuching)
-NOVST   25200 D  # Novosibirsk Summer Time (obsolete)
-NOVT    21600    # Novosibirsk Time (caution: this used to mean 25200)
+NOVST   Asia/Novosibirsk  # Novosibirsk Summer Time (obsolete)
+NOVT    Asia/Novosibirsk  # Novosibirsk Time
                  #     (Asia/Novosibirsk)
 NPT     20700    # Nepal Time
                  #     (Asia/Katmandu)
-OMSST   25200 D  # Omsk Summer Time (obsolete)
-OMST    21600    # Omsk Time (caution: this used to mean 25200)
+OMSST   Asia/Omsk  # Omsk Summer Time (obsolete)
+OMST    Asia/Omsk  # Omsk Time
                  #     (Asia/Omsk)
-PETST   46800 D  # Petropavlovsk-Kamchatski Summer Time (obsolete)
-PETT    43200    # Petropavlovsk-Kamchatski Time
+PETST   Asia/Kamchatka  # Petropavlovsk-Kamchatski Summer Time (obsolete)
+PETT    Asia/Kamchatka  # Petropavlovsk-Kamchatski Time
                  #     (Asia/Kamchatka)
 PHT     28800    # Philippine Time
                  #     (Asia/Manila)
@@ -336,14 +334,14 @@ PKT     18000    # Pakistan Time
                  #     (Asia/Karachi)
 PKST    21600 D  # Pakistan Summer Time
                  #     (Asia/Karachi)
-SGT     28800    # Singapore Time
+SGT     Asia/Singapore  # Singapore Time
                  #     (Asia/Singapore)
 TJT     18000    # Tajikistan Time
                  #     (Asia/Dushanbe)
-TMT     18000    # Turkmenistan Time
+TMT     Asia/Ashgabat  # Turkmenistan Time
                  #     (Asia/Ashgabat)
 ULAST   32400 D  # Ulan Bator Summer Time (obsolete)
-ULAT    28800    # Ulan Bator Time
+ULAT    Asia/Ulaanbaatar  # Ulan Bator Time
                  #     (Asia/Ulaanbaatar)
 UZST    21600 D  # Uzbekistan Summer Time
                  #     (Asia/Samarkand)
@@ -351,16 +349,16 @@ UZST    21600 D  # Uzbekistan Summer Time
 UZT     18000    # Uzbekistan Time
                  #     (Asia/Samarkand)
                  #     (Asia/Tashkent)
-VLAST   39600 D  # Vladivostok Summer Time (obsolete)
-VLAT    36000    # Vladivostok Time (caution: this used to mean 39600)
+VLAST   Asia/Vladivostok  # Vladivostok Summer Time (obsolete)
+VLAT    Asia/Vladivostok  # Vladivostok Time
                  #     (Asia/Vladivostok)
 XJT     21600    # Xinjiang Time
                  #     (Asia/Urumqi)
-YAKST   36000 D  # Yakutsk Summer Time (obsolete)
-YAKT    32400    # Yakutsk Time (caution: this used to mean 36000)
+YAKST   Asia/Yakutsk  # Yakutsk Summer Time (obsolete)
+YAKT    Asia/Yakutsk  # Yakutsk Time
                  #     (Asia/Yakutsk)
 YEKST   21600 D  # Yekaterinburg Summer Time (obsolete)
-YEKT    18000    # Yekaterinburg Time (caution: this used to mean 21600)
+YEKT    Asia/Yekaterinburg  # Yekaterinburg Time
                  #     (Asia/Yekaterinburg)
 
 #################### ATLANTIC ####################
@@ -406,9 +404,9 @@ AZOST       0 D  # Azores Summer Time
                  #     (Atlantic/Azores)
 AZOT    -3600    # Azores Time
                  #     (Atlantic/Azores)
-FKST   -10800    # Falkland Islands Summer Time (now used all year round)
+FKST    Atlantic/Stanley  # Falkland Islands Summer/Standard Time
                  #     (Atlantic/Stanley)
-FKT    -14400    # Falkland Islands Time (obsolete)
+FKT     Atlantic/Stanley  # Falkland Islands Time (obsolete)
 
 #################### AUSTRALIA ####################
 
@@ -443,7 +441,7 @@ AWST    28800    # Australian Western Standard Time
                  #     (Australia/Perth)
 CADT    37800 D  # Central Australia Daylight-Saving Time (not in zic)
 CAST    34200    # Central Australia Standard Time (not in zic)
-LHDT    39600 D  # Lord Howe Daylight Time
+LHDT    Australia/Lord_Howe  # Lord Howe Daylight Time
                  #     (Australia/Lord_Howe)
 LHST    37800    # Lord Howe Standard Time
                  #     (Australia/Lord_Howe)
@@ -639,9 +637,10 @@ MET      3600    # Middle Europe Time (not in zic)
 METDST   7200 D  # Middle Europe Summer Time (not in zic)
 MEZ      3600    # Mitteleuropaeische Zeit (German) (not in zic)
 MSD     14400 D  # Moscow Daylight Time (obsolete)
-MSK     10800    # Moscow Time (caution: this used to mean 14400)
+MSK     Europe/Moscow  # Moscow Time
                  #     (Europe/Moscow)
-VOLT    14400    # Volgograd Time (obsolete)
+                 #     (Europe/Volgograd)
+VOLT    Europe/Volgograd  # Volgograd Time (obsolete)
 WET         0    # Western Europe Time
                  #     (Africa/Casablanca)
                  #     (Africa/El_Aaiun)
@@ -659,7 +658,7 @@ WETDST   3600 D  # Western Europe Summer Time
 
 CXT     25200    # Christmas Island Time (Indian Ocean)
                  #     (Indian/Christmas)
-IOT     21600    # British Indian Ocean Territory (Chagos) (there was a timezone change recently in 1996)
+IOT     Indian/Chagos  # British Indian Ocean Territory (Chagos)
                  #     (Indian/Chagos)
 MUT     14400    # Mauritius Island Time
                  #     (Indian/Mauritius)
@@ -682,11 +681,11 @@ CHAST   45900    # Chatham Standard Time (New Zealand)
                  #     (Pacific/Chatham)
 CHUT    36000    # Chuuk Time
                  #     (Pacific/Chuuk)
-CKT    -36000    # Cook Islands Time (caution: this used to mean 43200)
+CKT     Pacific/Rarotonga  # Cook Islands Time
                  #     (Pacific/Rarotonga)
-EASST  -18000 D  # Easter Island Summer Time (Chile)
+EASST   Pacific/Easter  # Easter Island Summer Time (Chile)
                  #     (Pacific/Easter)
-EAST   -21600    # Easter Island Time (Chile)
+EAST    Pacific/Easter  # Easter Island Time (Chile)
                  #     (Pacific/Easter)
 FJST    46800 D  # Fiji Summer Time
                  #     (Pacific/Fiji)
@@ -701,9 +700,9 @@ GILT    43200    # Gilbert Islands Time
 HST    -36000    # Hawaiian Standard Time
                  #     (Pacific/Honolulu)
                  #     (Pacific/Johnston)
-KOST    39600    # Kosrae Time
+KOST    Pacific/Kosrae  # Kosrae Time
                  #     (Pacific/Kosrae)
-LINT    50400    # Line Islands Time (Kiribati)
+LINT    Pacific/Kiritimati  # Line Islands Time (Kiribati)
                  #     (Pacific/Kiritimati)
 MART   -34200    # Marquesas Time
                  #     (Pacific/Marquesas)
@@ -715,7 +714,7 @@ MPT     36000    # North Mariana Islands Time (not in zic)
 # Other timezones:
 #  - NFT: Norfolk Time (Pacific)
 NFT    -12600    # Newfoundland Time (not in zic)
-NUT    -39600    # Niue Time
+NUT     Pacific/Niue  # Niue Time
                  #     (Pacific/Niue)
 NZDT    46800 D  # New Zealand Daylight Time
                  #     (Antarctica/McMurdo)
@@ -725,7 +724,7 @@ NZST    43200    # New Zealand Standard Time
                  #     (Pacific/Auckland)
 PGT     36000    # Papua New Guinea Time
                  #     (Pacific/Port_Moresby)
-PHOT    46800    # Phoenix Islands Time (Kiribati)
+PHOT    Pacific/Enderbury  # Phoenix Islands Time (Kiribati)
                  #     (Pacific/Enderbury)
 PONT    39600    # Ponape Time (Micronesia)
                  #     (Pacific/Ponape)
@@ -733,7 +732,7 @@ PWT     32400    # Palau Time
                  #     (Pacific/Palau)
 TAHT   -36000    # Tahiti Time (zic says "TAHT", other sources "THAT")
                  #     (Pacific/Tahiti)
-TKT     46800    # Tokelau Time (caution: this used to mean -36000)
+TKT     Pacific/Fakaofo  # Tokelau Time
                  #     (Pacific/Fakaofo)
 TOT     46800    # Tonga Time
                  #     (Pacific/Tongatapu)
diff --git a/src/timezone/tznames/Europe.txt b/src/timezone/tznames/Europe.txt
index c6b37bdd5ed..421f8f18ad4 100644
--- a/src/timezone/tznames/Europe.txt
+++ b/src/timezone/tznames/Europe.txt
@@ -186,12 +186,13 @@ MET      3600    # Middle Europe Time (not in zic)
 METDST   7200 D  # Middle Europe Summer Time (not in zic)
 MEZ      3600    # Mitteleuropäische Zeit (German) (not in zic)
 MSD     14400 D  # Moscow Daylight Time (obsolete)
-MSK     10800    # Moscow Time (caution: this used to mean 14400)
+MSK     Europe/Moscow  # Moscow Time
                  #     (Europe/Moscow)
-SAMST   18000 D  # Samara Summer Time (obsolete)
-SAMT    14400    # Samara Time
+                 #     (Europe/Volgograd)
+SAMST   Europe/Samara  # Samara Summer Time (obsolete)
+SAMT    Europe/Samara  # Samara Time
                  #     (Europe/Samara)
-VOLT    14400    # Volgograd Time (obsolete)
+VOLT    Europe/Volgograd  # Volgograd Time (obsolete)
 WEST     3600 D  # Western Europe Summer Time
                  #     (Africa/Casablanca)
                  #     (Atlantic/Canary)
diff --git a/src/timezone/tznames/Indian.txt b/src/timezone/tznames/Indian.txt
index c77c9919a1c..634660075ff 100644
--- a/src/timezone/tznames/Indian.txt
+++ b/src/timezone/tznames/Indian.txt
@@ -23,7 +23,7 @@ EAT     10800    # East Africa Time
                  #     (Indian/Antananarivo)
                  #     (Indian/Comoro)
                  #     (Indian/Mayotte)
-IOT     21600    # British Indian Ocean Territory (Chagos) (there was a timezone change recently in 1996)
+IOT     Indian/Chagos  # British Indian Ocean Territory (Chagos)
                  #     (Indian/Chagos)
 MUT     14400    # Mauritius Island Time
                  #     (Indian/Mauritius)
diff --git a/src/timezone/tznames/Pacific.txt b/src/timezone/tznames/Pacific.txt
index 2f988140014..1d205589bbc 100644
--- a/src/timezone/tznames/Pacific.txt
+++ b/src/timezone/tznames/Pacific.txt
@@ -16,14 +16,14 @@ ChST    36000    # Chamorro Standard Time (lower case "h" is as in zic)
                  #     (Pacific/Saipan)
 CHUT    36000    # Chuuk Time
                  #     (Pacific/Chuuk)
-CKT    -36000    # Cook Islands Time (caution: this used to mean 43200)
+CKT     Pacific/Rarotonga  # Cook Islands Time
                  #     (Pacific/Rarotonga)
-EASST  -18000 D  # Easter Island Summer Time (Chile)
+EASST   Pacific/Easter  # Easter Island Summer Time (Chile)
                  #     (Pacific/Easter)
 # CONFLICT! EAST is not unique
 # Other timezones:
 #  - EAST: East Australian Standard Time (Australia)
-EAST   -21600    # Easter Island Time (Chile)
+EAST    Pacific/Easter  # Easter Island Time (Chile)
                  #     (Pacific/Easter)
 FJST    46800 D  # Fiji Summer Time (caution: this used to mean -46800)
                  #     (Pacific/Fiji)
@@ -38,9 +38,9 @@ GILT    43200    # Gilbert Islands Time
 HST    -36000    # Hawaiian Standard Time
                  #     (Pacific/Honolulu)
                  #     (Pacific/Johnston)
-KOST    39600    # Kosrae Time
+KOST    Pacific/Kosrae  # Kosrae Time
                  #     (Pacific/Kosrae)
-LINT    50400    # Line Islands Time (Kiribati)
+LINT    Pacific/Kiritimati  # Line Islands Time (Kiribati)
                  #     (Pacific/Kiritimati)
 MART   -34200    # Marquesas Time
                  #     (Pacific/Marquesas)
@@ -55,9 +55,9 @@ NCT     39600    # New Caledonia Time
 #  - NFT: Newfoundland Time (America)
 NFT     41400    # Norfolk Time
                  #     (Pacific/Norfolk)
-NRT     43200    # Nauru Time
+NRT     Pacific/Nauru  # Nauru Time
                  #     (Pacific/Nauru)
-NUT    -39600    # Niue Time
+NUT     Pacific/Niue  # Niue Time
                  #     (Pacific/Niue)
 NZDT    46800 D  # New Zealand Daylight Time
                  #     (Antarctica/McMurdo)
@@ -67,7 +67,7 @@ NZST    43200    # New Zealand Standard Time
                  #     (Pacific/Auckland)
 PGT     36000    # Papua New Guinea Time
                  #     (Pacific/Port_Moresby)
-PHOT    46800    # Phoenix Islands Time (Kiribati)
+PHOT    Pacific/Enderbury  # Phoenix Islands Time (Kiribati)
                  #     (Pacific/Enderbury)
 PONT    39600    # Ponape Time (Micronesia)
                  #     (Pacific/Ponape)
@@ -87,7 +87,7 @@ SST    -39600    # South Sumatran Time
                  #     (Pacific/Pago_Pago)
 TAHT   -36000    # Tahiti Time (zic says "TAHT", other sources "THAT")
                  #     (Pacific/Tahiti)
-TKT     46800    # Tokelau Time (caution: this used to mean -36000)
+TKT     Pacific/Fakaofo  # Tokelau Time
                  #     (Pacific/Fakaofo)
 TOT     46800    # Tonga Time
                  #     (Pacific/Tongatapu)
diff --git a/src/timezone/tznames/README b/src/timezone/tznames/README
index 6cb0ae88c93..c80caa37869 100644
--- a/src/timezone/tznames/README
+++ b/src/timezone/tznames/README
@@ -6,26 +6,29 @@ tznames
 This directory contains files with timezone sets for PostgreSQL.  The problem
 is that time zone abbreviations are not unique throughout the world and you
 might find out that a time zone abbreviation in the `Default' set collides
-with the one you wanted to use.  All other files except for `Default' are
-intended to override values from the `Default' set.  So you might already have
-a file here that serves your needs.  If not, you can create your own.
+with the one you wanted to use.  This can be fixed by selecting a timezone
+set that defines the abbreviation the way you want it.  There might already
+be a file here that serves your needs.  If not, you can create your own.
 
 In order to use one of these files, you need to set
 
    timezone_abbreviations = 'xyz'
 
 in any of the usual ways for setting a parameter, where xyz is the filename
-that contains the desired time zone names.
+that contains the desired time zone abbreviations.
 
-If you do not find an appropriate set of time zone names for your geographic
+If you do not find an appropriate set of abbreviations for your geographic
 location supplied here, please report this to <pgsql-hackers@postgresql.org>.
-Your set of time zone names can then be included in future releases.
+Your set of time zone abbreviations can then be included in future releases.
 For the time being you can always add your own set.
 
+Typically a custom abbreviation set is made by including the `Default' set
+and then adding or overriding abbreviations as necessary.  For examples,
+see the `Australia' and `India' files.
+
 The files named Africa.txt, etc, are not intended to be used directly as
 time zone abbreviation files. They contain reference definitions of time zone
-names that can be copied into a custom abbreviation file as needed.
-
-Note that these files (*.txt) are already a subset of the zic timezone
-database files: we tried to list only those time zones that (according to
-the zic timezone database) appear to be still in use.
+abbreviations that can be copied into a custom abbreviation file as needed.
+Note that these files (*.txt) are already a subset of the IANA timezone
+database files: we tried to list only those time zone abbreviations that
+(according to the IANA timezone database) appear to be still in use.
diff --git a/src/timezone/zic.c b/src/timezone/zic.c
index 13baf73d3c1..1a7ec68d7c0 100644
--- a/src/timezone/zic.c
+++ b/src/timezone/zic.c
@@ -1771,7 +1771,7 @@ writezone(const char *name, const char *string)
 
 				/* Print current timezone abbreviations if requested */
 				if (print_abbrevs &&
-					(ats[i] >= print_cutoff || i == thistimelim - 1))
+					(i == thistimelim - 1 || ats[i + 1] > print_cutoff))
 				{
 					unsigned char tm = typemap[types[i]];
 					char	   *thisabbrev = &thischars[indmap[abbrinds[tm]]];