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Commit7f28fc8

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Prefer timezone name "UTC" over alternative spellings.
tzdb 2019a made "UCT" a link to the "UTC" zone rather than a separatezone with its own abbreviation. Unfortunately, our code for choosing atimezone in initdb has an arbitrary preference for names earlier inthe alphabet, and so it would choose the spelling "UCT" over "UTC"when the system is running on a UTC zone.Commit23bd3ce was backpatched in order to address this issue, butthat code helps only when /etc/localtime exists as a symlink, and doesnothing to help on systems where /etc/localtime is a copy of a zonefile (as is the standard setup on FreeBSD and probably some otherplatforms too) or when /etc/localtime is simply absent (giving UTC asthe default).Accordingly, add a preference for the spelling "UTC", such that ifmultiple zone names have equally good content matches, we prefer thatname before applying the existing arbitrary rules. Also add a slightlylower preference for "Etc/UTC"; lower because that preserves theprevious behaviour of choosing the shorter name, but letting us stillchoose "Etc/UTC" over "Etc/UCT" when both exist but "UTC" doesnot (not common, but I've seen it happen).Backpatch all the way, because the tzdb change that sparked this issueis in those branches too.
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‎src/bin/initdb/findtimezone.c

Lines changed: 34 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -128,8 +128,11 @@ pg_load_tz(const char *name)
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* the C library's localtime() function. The database zone that matches
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* furthest into the past is the one to use. Often there will be several
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* zones with identical rankings (since the IANA database assigns multiple
131-
* names to many zones). We break ties arbitrarily by preferring shorter,
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* then alphabetically earlier zone names.
131+
* names to many zones). We break ties by first checking for "preferred"
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* names (such as "UTC"), and then arbitrarily by preferring shorter, then
133+
* alphabetically earlier zone names. (If we did not explicitly prefer
134+
* "UTC", we would get the alias name "UCT" instead due to alphabetic
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* ordering.)
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*
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* Many modern systems use the IANA database, so if we can determine the
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* system's idea of which zone it is using and its behavior matches our zone
@@ -602,6 +605,28 @@ check_system_link_file(const char *linkname, struct tztry *tt,
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#endif
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}
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/*
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* Given a timezone name, determine whether it should be preferred over other
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* names which are equally good matches. The output is arbitrary but we will
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* use 0 for "neutral" default preference.
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*
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* Ideally we'd prefer the zone.tab/zone1970.tab names, since in general those
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* are the ones offered to the user to select from. But for the moment, to
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* minimize changes in behaviour, simply prefer UTC over alternative spellings
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* such as UCT that otherwise cause confusion. The existing "shortest first"
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* rule would prefer "UTC" over "Etc/UTC" so keep that the same way (while
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* still preferring Etc/UTC over Etc/UCT).
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*/
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staticint
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zone_name_pref(constchar*zonename)
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{
623+
if (strcmp(zonename,"UTC")==0)
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return50;
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if (strcmp(zonename,"Etc/UTC")==0)
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return40;
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return0;
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}
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/*
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* Recursively scan the timezone database looking for the best match to
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* the system timezone behavior.
@@ -674,9 +699,13 @@ scan_available_timezones(char *tzdir, char *tzdirsub, struct tztry *tt,
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elseif (score==*bestscore)
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{
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/* Consider how to break a tie */
677-
if (strlen(tzdirsub)<strlen(bestzonename)||
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(strlen(tzdirsub)==strlen(bestzonename)&&
679-
strcmp(tzdirsub,bestzonename)<0))
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intnamepref= (zone_name_pref(tzdirsub)-
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zone_name_pref(bestzonename));
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if (namepref>0||
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(namepref==0&&
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(strlen(tzdirsub)<strlen(bestzonename)||
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(strlen(tzdirsub)==strlen(bestzonename)&&
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strcmp(tzdirsub,bestzonename)<0))))
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strlcpy(bestzonename,tzdirsub,TZ_STRLEN_MAX+1);
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}
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}

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