8000 Don't require dynamic timezone abbreviations to match underlying time… · s-monk/postgres@7430ac8 · GitHub
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Don't require dynamic timezone abbreviations to match underlying time zone.
Previously, we threw an error if a dynamic timezone abbreviation did not match any abbreviation recorded in the referenced IANA time zone entry. That seemed like a good consistency check at the time, but it turns out that a number of the abbreviations in the IANA database are things that Olson and crew made up out of whole cloth. Their current policy is to remove such names in favor of using simple numeric offsets. Perhaps unsurprisingly, a lot of these made-up abbreviations have varied in meaning over time, which meant that our commit b2cbced and later changes made them into dynamic abbreviations. So with newer IANA database versions that don't mention these abbreviations at all, we fail, as reported in bug #14307 from Neil Anderson. It's worse than just a few unused-in-the-wild abbreviations not working, because the pg_timezone_abbrevs view stops working altogether (since its underlying function tries to compute the whole view result in one call). We considered deleting these abbreviations from our abbreviations list, but the problem with that is that we can't stay ahead of possible future IANA changes. Instead, let's leave the abbreviations list alone, and treat any "orphaned" dynamic abbreviation as just meaning the referenced time zone. It will behave a bit differently than it used to, in that you can't any longer override the zone's standard vs. daylight rule by using the "wrong" abbreviation of a pair, but that's better than failing entirely. (Also, this solution can be interpreted as adding a small new feature, which is that any abbreviation a user wants can be defined as referencing a time zone name.) Back-patch to all supported branches, since this problem affects all of them when using tzdata 2016f or newer. Report: <20160902031551.15674.67337@wrigleys.postgresql.org> Discussion: <6189.1472820913@sss.pgh.pa.us>
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‎doc/src/sgml/catalogs.sgml

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Original file line numberDiff line numberDiff line change
@@ -9184,6 +9184,13 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
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</tgroup>
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</table>
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<para>
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While most timezone abbreviations represent fixed offsets from UTC,
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there are some that have historically varied in value
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(see <xref linkend="datetime-config-files"> for more information).
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In such cases this view presents their current meaning.
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</para>
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91879194
</sect1>
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<sect1 id="view-pg-timezone-names">

‎doc/src/sgml/datetime.sgml

Lines changed: 30 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -384,19 +384,38 @@
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<para>
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A <replaceable>zone_abbreviation</replaceable> is just the abbreviation
387-
being defined. The <replaceable>offset</replaceable> is the equivalent
388-
offset in seconds from UTC, positive being east from Greenwich and
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negative being west. For example, -18000 would be five hours west
390-
of Greenwich, or North American east coast standard time. <literal>D</>
391-
indicates that the zone name represents local daylight-savings time rather
392-
than standard time. Alternatively, a <replaceable>time_zone_name</> can
393-
be given, in which case that time zone definition is consulted, and the
394-
abbreviation's meaning in that zone is used. This alternative is
395-
recommended only for abbreviations whose meaning has historically varied,
396-
as looking up the meaning is noticeably more expensive than just using
397-
a fixed integer value.
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being defined. An <replaceable>offset</replaceable> is an integer giving
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the equivalent offset in seconds from UTC, positive being east from
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Greenwich and negative being west. For example, -18000 would be five
390+
hours west of Greenwich, or North American east coast standard time.
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<literal>D</> indicates that the zone name represents local
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daylight-savings time rather than standard time.
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</para>
399394

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<para>
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Alternatively, a <replaceable>time_zone_name</> can be given, referencing
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a zone name defined in the IANA timezone database. The zone's definition
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is consulted to see whether the abbreviation is or has been in use in
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that zone, and if so, the appropriate meaning is used &mdash; that is,
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the meaning that was currently in use at the timestamp whose value is
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being determined, or the meaning in use immediately before that if it
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wasn't current at that time, or the oldest meaning if it was used only
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after that time. This behavior is essential for dealing with
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abbreviations whose meaning has historically varied. It is also allowed
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to define an abbreviation in terms of a zone name in which that
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abbreviation does not appear; then using the abbreviation is just
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equivalent to writing out the zone name.
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</para>
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<tip>
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<para>
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Using a simple integer <replaceable>offset</replaceable> is preferred
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when defining an abbreviation whose offset from UTC has never changed,
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as such abbreviations are much cheaper to process than those that
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require consulting a time zone definition.
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</para>
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</tip>
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400419
<para>
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The <literal>@INCLUDE</> syntax allows inclusion of another file in the
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<filename>.../share/timezonesets/</> directory. Inclusion can be nested,

‎src/backend/utils/adt/datetime.c

Lines changed: 64 additions & 21 deletions
Original file line numberDiff line numberDiff line change
@@ -52,8 +52,9 @@ static void AdjustFractDays(double frac, struct pg_tm 6D40 * tm, fsec_t *fsec,
5252
int scale);
5353
static int DetermineTimeZoneOffsetInternal(struct pg_tm * tm, pg_tz *tzp,
5454
pg_time_t *tp);
55-
static int DetermineTimeZoneAbbrevOffsetInternal(pg_time_t t, const char *abbr,
56-
pg_tz *tzp, int *isdst);
55+
static bool DetermineTimeZoneAbbrevOffsetInternal(pg_time_t t,
56+
const char *abbr, pg_tz *tzp,
57+
int *offset, int *isdst);
5758
static pg_tz *FetchDynamicTimeZone(TimeZoneAbbrevTable *tbl, const datetkn *tp);
5859

5960

@@ -1620,19 +1621,40 @@ DetermineTimeZoneOffsetInternal(struct pg_tm * tm, pg_tz *tzp, pg_time_t *tp)
16201621
* This differs from the behavior of DetermineTimeZoneOffset() in that a
16211622
* standard-time or daylight-time abbreviation forces use of the corresponding
16221623
* GMT offset even when the zone was then in DS or standard time respectively.
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* (However, that happens only if we can match the given abbreviation to some
1625+
* abbreviation that appears in the IANA timezone data. Otherwise, we fall
1626+
* back to doing DetermineTimeZoneOffset().)
16231627
*/
16241628
int
16251629
DetermineTimeZoneAbbrevOffset(struct pg_tm * tm, const char *abbr, pg_tz *tzp)
16261630
{
16271631
pg_time_t t;
1632+
int zone_offset;
1633+
int abbr_offset;
1634+
int abbr_isdst;
16281635

16291636
/*
16301637
* Compute the UTC time we want to probe at. (In event of overflow, we'll
16311638
* probe at the epoch, which is a bit random but probably doesn't matter.)
16321639
*/
1633-
(void) DetermineTimeZoneOffsetInternal(tm, tzp, &t);
1640+
zone_offset = DetermineTimeZoneOffsetInternal(tm, tzp, &t);
16341641

1635-
return DetermineTimeZoneAbbrevOffsetInternal(t, abbr, tzp, &tm->tm_isdst);
1642+
/*
1643+
* Try to match the abbreviation to something in the zone definition.
1644+
*/
1645+
if (DetermineTimeZoneAbbrevOffsetInternal(t, abbr, tzp,
1646+
&abbr_offset, &abbr_isdst))
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{
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/* Success, so use the abbrev-specific answers. */
1649+
tm->tm_isdst = abbr_isdst;
1650+
return abbr_offset;
1651+
}
1652+
1653+
/*
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* No match, so use the answers we already got from
1655+
* DetermineTimeZoneOffsetInternal.
1656+
*/
1657+
return zone_offset;
16361658
}
16371659

16381660

@@ -1646,19 +1668,41 @@ DetermineTimeZoneAbbrevOffsetTS(TimestampTz ts, const char *abbr,
16461668
pg_tz *tzp, int *isdst)
16471669
{
16481670
pg_time_t t = timestamptz_to_time_t(ts);
1671+
int zone_offset;
1672+
int abbr_offset;
1673+
int tz;
1674+
struct pg_tm tm;
1675+
fsec_t fsec;
16491676

1650-
return DetermineTimeZoneAbbrevOffsetInternal(t, abbr, tzp, isdst);
1677+
/*
1678+
* If the abbrev matches anything in the zone data, this is pretty easy.
1679+
*/
1680+
if (DetermineTimeZoneAbbrevOffsetInternal(t, abbr, tzp,
1681+
&abbr_offset, isdst))
1682+
return abbr_offset;
1683+
1684+
/*
1685+
* Else, break down the timestamp so we can use DetermineTimeZoneOffset.
1686+
*/
1687+
if (timestamp2tm(ts, &tz, &tm, &fsec, NULL, tzp) != 0)
1688+
ereport(ERROR,
1689+
(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
1690+
errmsg("timestamp out of range")));
1691+
1692+
zone_offset = DetermineTimeZoneOffset(&tm, tzp);
1693+
*isdst = tm.tm_isdst;
1694+
return zone_offset;
16511695
}
16521696

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16541698
/* DetermineTimeZoneAbbrevOffsetInternal()
16551699
*
16561700
* Workhorse for above two functions: work from a pg_time_t probe instant.
1657-
* DST status is returned into *isdst.
1701+
* On success, return GMT offset and DST status into *offset and *isdst.
16581702
*/
1659-
static int
1660-
DetermineTimeZoneAbbrevOffsetInternal(pg_time_t t, const char *abbr,
1661-
pg_tz *tzp, int *isdst)
1703+
static bool
1704+
DetermineTimeZoneAbbrevOffsetInternal(pg_time_t t, const char *abbr, pg_tz *tzp,
1705+
int *offset, int *isdst)
16621706
{
16631707
char upabbr[TZ_STRLEN_MAX + 1];
16641708
unsigned char *p;
@@ -1670,18 +1714,17 @@ DetermineTimeZoneAbbrevOffsetInternal(pg_time_t t, const char *abbr,
16701714
*p = pg_toupper(*p);
16711715

16721716
/* Look up the abbrev's meaning at this time in this zone */
1673-
if (!pg_interpret_timezone_abbrev(upabbr,
1674-
&t,
1675-
&gmtoff,
1676-
isdst,
1677-
tzp))
1678-
ereport(ERROR,
1679-
(errcode(ERRCODE_CONFIG_FILE_ERROR),
1680-
errmsg("time zone abbreviation \"%s\" is not used in time zone \"%s\"",
1681-
abbr, pg_get_timezone_name(tzp))));
1682-
1683-
/* Change sign to agree with DetermineTimeZoneOffset() */
1684-
return (int) -gmtoff;
1717+
if (pg_interpret_timezone_abbrev(upabbr,
1718+
&t,
1719+
&gmtoff,
1720+
isdst,
1721+
tzp))
1722+
{
1723+
/* Change sign to agree with DetermineTimeZoneOffset() */
1724+
*offset = (int) -gmtoff;
1725+
return true;
1726+
}
1727+
return false;
16851728
}
16861729

16871730

‎src/test/regress/expected/timestamptz.out

Lines changed: 20 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2538,3 +2538,23 @@ SELECT '2007-12-09 07:30:00 UTC'::timestamptz AT TIME ZONE 'VET';
25382538
Sun Dec 09 03:00:00 2007
25392539
(1 row)
25402540

2541+
--
2542+
-- Test that the pg_timezone_names and pg_timezone_abbrevs views are
2543+
-- more-or-less working. We can't test their contents in any great detail
2544+
-- without the outputs changing anytime IANA updates the underlying data,
2545+
-- but it seems reasonable to expect at least one entry per major meridian.
2546+
-- (At the time of writing, the actual counts are around 38 because of
2547+
-- zones using fractional GMT offsets, so this is a pretty loose test.)
2548+
--
2549+
select count(distinct utc_offset) >= 24 as ok from pg_timezone_names;
2550+
ok
2551+
----
2552+
t
2553+
(1 row)
2554+
2555+
select count(distinct utc_offset) >= 24 as ok from pg_timezone_abbrevs;
2556+
ok
2557+
----
2558+
t
2559+
(1 row)
2560+

‎src/test/regress/sql/timestamptz.sql

Lines changed: 11 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -449,3 +449,14 @@ SELECT '2007-12-09 07:00:00 UTC'::timestamptz AT TIME ZONE 'VET';
449449
SELECT '2007-12-09 07:00:01 UTC'::timestamptz AT TIME ZONE 'VET';
450450
SELECT '2007-12-09 07:29:59 UTC'::timestamptz AT TIME ZONE 'VET';
451451
SELECT '2007-12-09 07:30:00 UTC'::timestamptz AT TIME ZONE 'VET';
452+
453+
--
454+
-- Test that the pg_timezone_names and pg_timezone_abbrevs views are
455+
-- more-or-less working. We can't test their contents in any great detail
456+
-- without the outputs changing anytime IANA updates the underlying data,
457+
-- but it seems reasonable to expect at least one entry per major meridian.
458+
-- (At the time of writing, the actual counts are around 38 because of
459+
-- zones using fractional GMT offsets, so this is a pretty loose test.)
460+
--
461+
select count(distinct utc_offset) >= 24 as ok from pg_timezone_names;
462+
select count(distinct utc_offset) >= 24 as ok from pg_timezone_abbrevs;

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