diff options
Diffstat (limited to 'doc/src/sgml/datatype.sgml')
| -rw-r--r-- | doc/src/sgml/datatype.sgml | 39 |
1 files changed, 28 insertions, 11 deletions
diff --git a/doc/src/sgml/datatype.sgml b/doc/src/sgml/datatype.sgml index 3e83dbbe4c0..223ba6ade8e 100644 --- a/doc/src/sgml/datatype.sgml +++ b/doc/src/sgml/datatype.sgml @@ -2325,7 +2325,7 @@ 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</> (Olson) time zone database for information about + IANA (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. @@ -2390,8 +2390,8 @@ January 8 04:05:06 1999 PST The recognized time zone names are listed in the <literal>pg_timezone_names</literal> view (see <xref linkend="view-pg-timezone-names">). - <productname>PostgreSQL</productname> uses the widely-used - <literal>zoneinfo</> time zone data for this purpose, so the same + <productname>PostgreSQL</productname> uses the widely-used IANA + time zone data for this purpose, so the same time zone names are also recognized by much other software. </para> </listitem> @@ -2427,7 +2427,7 @@ January 8 04:05:06 1999 PST When a daylight-savings zone abbreviation is present, it is assumed to be used according to the same daylight-savings transition rules used in the - <literal>zoneinfo</> time zone database's <filename>posixrules</> entry. + IANA time zone database's <filename>posixrules</> entry. In a standard <productname>PostgreSQL</productname> installation, <filename>posixrules</> is the same as <literal>US/Eastern</>, so that POSIX-style time zone specifications follow USA daylight-savings @@ -2438,9 +2438,25 @@ January 8 04:05:06 1999 PST </itemizedlist> In short, this is the difference between abbreviations - and full names: abbreviations always represent a fixed offset from - UTC, whereas most of the full names imply a local daylight-savings time - rule, and so have two possible UTC offsets. + and full names: abbreviations represent a specific offset from UTC, + whereas many of the full names imply a local daylight-savings time + rule, and so have two possible UTC offsets. As an example, + <literal>2014-06-04 12:00 America/New_York</> represents noon local + time in New York, which for this particular date was Eastern Daylight + Time (UTC-4). So <literal>2014-06-04 12:00 EDT</> specifies that + same time instant. But <literal>2014-06-04 12:00 EST</> specifies + noon Eastern Standard Time (UTC-5), regardless of whether daylight + savings was nominally in effect on that date. + </para> + + <para> + To complicate matters, some jurisdictions have used the same timezone + abbreviation to mean different UTC offsets at different times; for + example, in Moscow <literal>MSK</> has meant UTC+3 in some years and + UTC+4 in others. <application>PostgreSQL</> interprets such + abbreviations according to whatever they meant (or had most recently + meant) on the specified date; but, as with the <literal>EST</> example + above, this is not necessarily the same as local civil time on that date. </para> <para> @@ -2457,13 +2473,14 @@ January 8 04:05:06 1999 PST </para> <para> - In all cases, timezone names are recognized case-insensitively. - (This is a change from <productname>PostgreSQL</productname> versions - prior to 8.2, which were case-sensitive in some contexts but not others.) + In all cases, timezone names and abbreviations are recognized + case-insensitively. (This is a change from <productname>PostgreSQL</> + versions prior to 8.2, which were case-sensitive in some contexts but + not others.) </para> <para> - Neither full names nor abbreviations are hard-wired into the server; + Neither timezone names nor abbreviations are hard-wired into the server; they are obtained from configuration files stored under <filename>.../share/timezone/</> and <filename>.../share/timezonesets/</> of the installation directory |