I had a brain fade in commit d32899157, and used 2:30AM as the
example timestamp for both spring-forward and fall-back cases.
But it's not actually ambiguous at all in the fall-back case,
because that transition is from 2AM to 1AM under USA rules.
Fix the example to use 1:30AM, which *is* ambiguous.
Noted while answering a question from Aleksander Alekseev.
Back-patch to all supported branches.
Discussion: https://postgr.es/m/2191355.1641828552@sss.pgh.pa.us
For some reason, the "julian" option for extract()/date_part() has
never gotten listed in the manual. Also, while Appendix B mentioned
in passing that we don't conform to the usual astronomical definition
that a Julian date starts at noon UTC, it was kind of vague about what
we do instead. Clarify that, and add an example showing how to get
the astronomical definition if you want it.
It's been like this for ages, so back-patch to all supported branches.
Discussion: https://postgr.es/m/1197050.1619123213@sss.pgh.pa.us
The IANA tzcode library has a feature to read a time zone file named
"posixrules" and apply the daylight-savings transition dates and times
therein, when it is given a POSIX-style time zone specification that
lacks an explicit transition rule. However, there's a problem with
that code: it doesn't work for dates past the Y2038 time_t rollover.
(Effectively, all times beyond that point are treated as standard
time.) The IANA crew regard this feature as legacy, so their plan is
to remove it not fix it. The time frame in which that will happen
is unclear, but presumably it'll happen well before 2038.
Moreover, effective with the next IANA data update (probably this
fall), the recommended default will be to not install a "posixrules"
file in the first place. The time frame in which tzdata packagers
might adopt that suggestion is likewise unclear, but at least some
platforms will probably do it in the next year or so. While we could
ignore that recommendation so far as PG-supplied tzdata trees are
concerned, builds using --with-system-tzdata will be subject to
whatever the platform's tzdata packager decides to do.
Thus, whether or not we do anything, some increasing fraction of
Postgres users will be exposed to the behavior observed when there
is no "posixrules" file; and if we do nothing, we'll have essentially
no control over the timing of that change.
The best thing to do to ameliorate the uncertainty seems to be to
proactively remove the posixrules-reading feature. If we do that in
a scheduled release then at least we can release-note the behavioral
change, rather than having users be surprised by it after a routine
tzdata update.
The change in question is fairly minor anyway: to be affected,
you have to be using a POSIX-style timezone spec, it has to not
have an explicit rule, and it has to not be one of the four traditional
continental-USA zone names (EST5EDT, CST6CDT, MST7MDT, or PST8PDT),
as those are special-cased. Since the default "posixrules" file
provides USA DST rules, the number of people who are likely to find
such a zone spec useful is probably quite small. Moreover, the
fallback behavior with no explicit rule and no "posixrules" file is to
apply current USA rules, so the only thing that really breaks is the
DST transitions in years before 2007 (and you get the countervailing
fix that transitions after 2038 will be applied).
Now, some installations might have replaced the "posixrules" file,
allowing e.g. EU rules to be applied to a POSIX-style timezone spec.
That won't work anymore. But it's not exactly clear why this solution
would be preferable to using a regular named zone. In any case, given
the Y2038 issue, we need to be pushing users to stop depending on this.
Back-patch into v13; it hasn't been released yet, so it seems OK to
change its behavior. (Personally I think we ought to back-patch
further, but I've been outvoted.)
Discussion: https://postgr.es/m/1390.1562258309@sss.pgh.pa.us
Discussion: https://postgr.es/m/20200621211855.6211-1-eggert@cs.ucla.edu
The IANA time zone folk have deprecated use of a "posixrules" file in
the tz database. While for now it's our choice whether to keep
supplying one in our own builds, installations built with
--with-system-tzdata will soon be needing to cope with that file not
being present, at least on some platforms.
This causes a problem for the horology test, which expected the
nonstandard POSIX zone spec "CST7CDT" to apply pre-2007 US daylight
savings rules. That does happen if the posixrules file supplies such
information, but otherwise the test produces undesired results.
To fix, add an explicit transition date rule that matches 2005 practice.
(We could alternatively have switched the test to use some real time
zone, but it seems useful to have coverage of this type of zone spec.)
While at it, update a documentation example that also relied on
"CST7CDT"; use a real-world zone name instead. Also, document why
the zone names EST5EDT, CST6CDT, MST7MDT, PST8PDT aren't subject to
similar failures when "posixrules" is missing.
Back-patch to all supported branches, since the hazard is the same
for all.
Discussion: https://postgr.es/m/1665379.1592581287@sss.pgh.pa.us
We'd glossed over most of this complexity for years, but it's hard
to avoid writing it all down now, so that we can explain what happens
when there's no "posixrules" file in the IANA time zone database.
That was at best a tiny minority situation till now, but it's likely
to become quite common in the future, so we'd better explain it.
Nonetheless, we don't really encourage people to use POSIX zone specs;
picking a named zone is almost always what you really want, unless
perhaps you're stuck with an out-of-date zone database. Therefore,
let's shove all this detail into an appendix.
Patch by me; thanks to Robert Haas for help with some awkward wording.
Discussion: https://postgr.es/m/1390.1562258309@sss.pgh.pa.us
The source code comments documented this, but the user-facing docs, not
so much. Add a section to Appendix B that discusses it.
In passing, improve a couple other things in Appendix B --- notably,
a long-obsolete claim that time zone abbreviations are looked up in
a fixed table.
Per bug #15527 from Michael Davidson.
Discussion: https://postgr.es/m/15527-f1be0b4dc99ebbe7@postgresql.org
Since some preparation work had already been done, the only source
changes left were changing empty-element tags like <xref linkend="foo">
to <xref linkend="foo"/>, and changing the DOCTYPE.
The source files are still named *.sgml, but they are actually XML files
now. Renaming could be considered later.
In the build system, the intermediate step to convert from SGML to XML
is removed. Everything is build straight from the source files again.
The OpenSP (or the old SP) package is no longer needed.
The documentation toolchain instructions are updated and are much
simpler now.
Peter Eisentraut, Alexander Lakhin, Jürgen Purtz
For DocBook XML compatibility, don't use SGML empty tags (</>) anymore,
replace by the full tag name. Add a warning option to catch future
occurrences.
Alexander Lakhin, Jürgen Purtz
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 b2cbced9e 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>
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.
Get rid of section 8.5.6 (Date/Time Internals), which appears to confuse
people more than it helps, and anyway discussion of Postgres' internal
datetime calculation methods seems pretty out of place here. Instead,
make datatype.sgml just say that we follow the Gregorian calendar (a bit
of specification not previously present anywhere in that chapter :-()
and link to the History of Units appendix for more info. Do some mild
editorialization on that appendix, too, to make it clearer that we are
following proleptic Gregorian calendar rules rather than anything more
historically accurate.
Per a question from Florence Cousin and subsequent discussion in
pgsql-docs.
noise words for the last twelve years, for compatibility with Berkeley-era
output formatting of the special INVALID values for those datatypes.
Considering that the datatypes themselves have been deprecated for awhile,
this is taking backwards compatibility a little far. Per gripe from Josh
Berkus.
outside the 32-bit-time_t range. Also, refer to Olson's tz database
as the 'zoneinfo' database, a name that upstream sometimes uses, not
'zic database' which they never use.
to ensure that the resulting webpages have predictable URLs, instead of
ever-changing numeric IDs. The new contrib docs were the biggest
offender, but some old stuff had the problem too. Also, rename a couple
of new contrib sgml files for consistency's sake.
Standard English uses "may", "can", and "might" in different ways:
may - permission, "You may borrow my rake."
can - ability, "I can lift that log."
might - possibility, "It might rain today."
Unfortunately, in conversational English, their use is often mixed, as
in, "You may use this variable to do X", when in fact, "can" is a better
choice. Similarly, "It may crash" is better stated, "It might crash".
Also update two error messages mentioned in the documenation to match.
input routines. Remove the former "DecodePosixTimezone" function in favor of
letting the zic code handle POSIX-style zone specs (see tzparse()). In
particular this means that "PST+3" now means the same as "-03", whereas it
used to mean "-11" --- the zone abbreviation is effectively just a noise word
in this syntax. Make sure that all named and POSIX-style zone names will be
parsed as a single token. Fix long-standing bogosities in printing and input
of fractional-hour timezone offsets (since the tzparse() code will accept
these, we'd better make 'em work). Also correct an error in the original
coding of the zic-zone-name patch: in "timestamp without time zone" input,
zone names are supposed to be allowed but ignored, but the coding was such
that the zone changed the interpretation anyway.
configuration files that can be altered by a DBA. The australian_timezones
GUC setting disappears, replaced by a timezone_abbreviations setting (set this
to 'Australia' to get the effect of australian_timezones). The list of zone
names defined by default has undergone a bit of cleanup, too. Documentation
still needs some work --- in particular, should we fix Table B-4, or just get
rid of it? Joachim Wieland, with some editorializing by moi.
compatibility for release 7.2 and earlier. I have not altered any
mentions of release 7.3 or later. The release notes were not modified,
so the changes are still documented, just not in the main docs.
in the zic database or zone names found in the date token table. This
preserves the old ability to do AT TIME ZONE 'PST' along with the new
ability to do AT TIME ZONE 'PST8PDT'. Per gripe from Bricklen Anderson.
Also, fix some inconsistencies in usage of TZ_STRLEN_MAX --- the old
code had the potential for one-byte buffer overruns, though given
alignment considerations it's unlikely there was any real risk.
"AT TIME ZONE", and not just the shorlist previously available. For
example:
SELECT CURRENT_TIMESTAMP AT TIME ZONE 'Europe/London';
works fine now. It will also obey whatever DST rules were in effect at
just that date, which the previous implementation did not.
It also supports the AT TIME ZONE on the timetz datatype. The whole
handling of DST is a bit bogus there, so I chose to make it use whatever
DST rules are in effect at the time of executig the query. not sure if
anybody is actuallyi *using* timetz though, it seems pretty
unpredictable just because of this...
Magnus Hagander
---------------------------------------------------------------------------
1. In keeping with the recent discussion that there should be more
said about views, stored procedures, and triggers, in the tutorial, I
have added a bit of verbiage to that end.
2. Some formatting changes to the datetime discussion, as well as
addition of a citation of a relevant book on calendars.
Christopher Browne
said about views, stored procedures, and triggers, in the tutorial, I
have added a bit of verbiage to that end.
2. Some formatting changes to the datetime discussion, as well as
addition of a citation of a relevant book on calendars.
Christopher Browne
heuristic determination of day vs month in date/time input. Add the
ability to specify that input is interpreted as yy-mm-dd order (which
formerly worked, but only for yy greater than 31). DateStyle's input
component now has the preferred spellings DMY, MDY, or YMD; the older
keywords European and US are now aliases for the first two of these.
Per recent discussions on pgsql-general.
Bruce Momjian
Peter Eisentraut
Tom Lane
Michael Paquier
Peter Eisentraut
Magnus Hagander
Neil Conway
PostgreSQL Daemon