[Bug 868395] Re: Bug in Europe/Russia timezones

[Benjamin Drung]

I can reproduce this slowdown in a Ubuntu jammy chroot:

```
apt install -y gcc tzdata
printf '#include <time.h>\n#include <stdio.h>\n\nint main() {\n  time_t t = time(0);\n  int i;\n  struct tm result;\n  for(i=0; i < 10000000; i++)\n    localtime_r(&t, &result);\n  puts(ctime(&t));\n  return 0;\n}\n' > bug.c
gcc ./bug.c
time ./a.out
ln -sf /usr/share/zoneinfo/Europe/Moscow /etc/localtime
dpkg-reconfigure --frontend noninteractive tzdata
time ./a.out
```

On my machine it takes 0.284s for Etc/UTC but 1.276s for Europe/Moscow.
Europe/Berlin takes 0.378s. This needs to be reported upstream.

** Changed in: tzdata (Ubuntu)
       Status: Confirmed => Triaged

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Title:
  Bug in Europe/Russia timezones

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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