[Bug 868395] Re: localtime_r multiple times slower for Europe/Moscow timezone

[Guy Harris]

Not just Russia - on 22.04:

$ time TZ=Etc/UTC ./bug
Tue Jan 10 23:46:13 2023


real	0m0.537s
user	0m0.529s
sys	0m0.004s
$ time TZ=Europe/Berlin ./bug
Wed Jan 11 00:46:31 2023


real	0m0.677s
user	0m0.670s
sys	0m0.004s
$ time TZ=Europe/Moscow ./bug
Wed Jan 11 02:46:50 2023


real	0m1.908s
user	0m1.902s
sys	0m0.000s
$ time TZ=America/Los_Angeles ./bug
Tue Jan 10 15:55:52 2023


real	0m0.673s
user	0m0.663s
sys	0m0.004s
$ time TZ=Asia/Tokyo ./bug
Wed Jan 11 08:58:32 2023


real	0m1.807s
user	0m1.795s
sys	0m0.005s

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https://bugs.launchpad.net/bugs/868395

Title:
  localtime_r multiple times slower for Europe/Moscow timezone

Status in tzdata package in Ubuntu:
  Triaged

Bug description:
  In version tzdata-2011j (tzdata-2011k also affected) was founded strange bug in russian timezones.
  Because of a law "On the Calculation of Time" there were changes in zone like:
  3:00   Russia  MSK/MSD 2011
  changed to:
  3:00   Russia  MSK/MSD 2011 Mar 27 2:00s
  4:00   -   MSK
  But if no rule used for this change (using "-" instead of rule "Russia"), calling of system function localtime_r() takes more time (takes more than 40% time longer).
  I used following code for measuring:
  ==============================
  #include <time.h>
  #include <stdio.h>

  int main() {
    time_t t = time(0);
    int i;
    struct tm result;
    for(i=0; i < 10000000; i++)
      localtime_r(&t, &result);
    puts(ctime(&t));
    return 0;
  }
  ==============================
  and also this sql code in mysql db:
  select benchmark(1000000, from_unixtime(1317044847));
  For example, when I'm using new tzdata-2011j results are:
  1. time ./a.out (c code)
  real	0m5.165s
  user	0m5.140s
  sys	0m0.000s
  2. sql query
  mysql> select benchmark(1000000, from_unixtime(1317044847));
  +-----------------------------------------------+
  | benchmark(1000000, from_unixtime(1317044847)) |
  +-----------------------------------------------+
  |                                             0 | 
  +-----------------------------------------------+
  1 row in set (1.03 sec).
  And when I'm using old tzdata-2008b:
  1. time ./a.out (c code)
  real	0m1.675s
  user	0m1.450s
  sys	0m0.000s
  2. sql query
  mysql> select benchmark(1000000, from_unixtime(1317044847));
  +-----------------------------------------------+
  | benchmark(1000000, from_unixtime(1317044847)) |
  +-----------------------------------------------+
  |                                             0 | 
  +-----------------------------------------------+
  1 row in set (0.65 sec)

  This bug seemed critical on high loaded systems (for example, for
  databases that using unix timestamps).

  My configuration was:
  Description:	Ubuntu 8.04.1
  Release:	8.04
  Packages: 2011j~repack-0ubuntu0.8.04 and 2008b-1ubuntu1

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