$ perlbrew switch perl-5.16.3
$ perl -E '%h=map {$_=>1} (1..10); say join ",",keys %h for 1..3'
6,3,7,9,2,8,1,4,10,5
6,3,7,9,2,8,1,4,10,5
6,3,7,9,2,8,1,4,10,5
$ perl -E '%h=map {$_=>1} (1..10); say join ",",keys %h for 1..3'
6,3,7,9,2,8,1,4,10,5
6,3,7,9,2,8,1,4,10,5
6,3,7,9,2,8,1,4,10,5
$ perlbrew switch perl-5.18.0
$ perl -E '%h=map {$_=>1} (1..10); say join ",",keys %h for 1..3'
10,2,8,3,6,9,5,4,1,7
10,2,8,3,6,9,5,4,1,7
10,2,8,3,6,9,5,4,1,7
$ perl -E '%h=map {$_=>1} (1..10); say join ",",keys %h for 1..3'
4,6,9,1,10,3,2,7,8,5
4,6,9,1,10,3,2,7,8,5
4,6,9,1,10,3,2,7,8,5
Now each execution has its own hash key ordering (but hash key ordering is the same for the duration of the execution until you insert a new key.)
perl-5.18 increases the chance that keys will be reordered when inserts happen:
$ perlbrew switch perl-5.16.3
$ perl -E 'for (1..20) { $h{$_}=1; say join ",",keys %h }'
1
1,2
1,3,2
4,1,3,2
4,1,3,2,5
6,4,1,3,2,5
6,4,1,3,7,2,5
6,3,7,2,8,1,4,5
6,3,7,9,2,8,1,4,5
6,3,7,9,2,8,1,4,10,5
6,11,3,7,9,2,8,1,4,10,5
6,11,3,7,9,12,2,8,1,4,10,5
6,11,3,7,9,12,2,8,1,4,13,10,5
6,11,3,7,9,12,2,14,8,1,4,13,10,5
6,11,3,7,9,12,2,15,14,8,1,4,13,10,5
11,7,2,1,16,13,6,3,9,12,14,15,8,4,10,5
11,7,17,2,1,16,13,6,3,9,12,14,15,8,4,10,5
11,7,17,2,1,18,16,13,6,3,9,12,14,15,8,4,10,5
11,7,17,2,1,18,16,13,6,3,9,12,14,15,8,4,19,10,5
11,7,17,2,1,18,16,13,6,3,9,12,20,14,15,8,4,19,10,5
$ perlbrew switch perl-5.18.0
$ perl -E 'for (1..20) { $h{$_}=1; say join ",",keys %h }'
1
2,1
1,2,3
2,4,1,3
4,1,2,5,3
2,4,1,5,3,6
4,1,2,6,5,7,3
7,8,1,3,5,6,2,4
4,2,6,3,5,8,1,9,7
9,7,8,1,6,3,5,10,4,2
9,7,11,8,1,6,5,10,3,4,2
11,8,1,7,9,2,12,4,5,10,3,6
4,13,12,2,6,3,5,10,8,1,11,9,7
11,14,8,1,7,9,2,12,4,13,5,10,3,6
4,13,12,15,2,6,3,5,10,14,8,1,11,9,7
9,16,7,8,14,3,13,12,15,2,1,11,6,5,10,4
5,10,17,6,4,11,1,3,2,12,15,13,16,7,9,8,14
4,17,6,5,10,1,11,13,12,15,2,18,3,8,14,9,16,7
17,6,5,10,4,1,11,19,3,13,12,15,2,18,9,16,7,8,14
11,1,4,5,10,17,6,8,14,16,7,9,2,18,20,12,15,13,3,19
This can be controlled with the
PERL_PERTURB_KEYS environment variable
$ perlbrew switch perl-5.18.0
$ PERL_PERTURB_KEYS=0 perl -E'for (1..20) { $h{$_}=1; say join ",",keys %h }'
1
2,1
3,2,1
3,2,1,4
5,3,2,1,4
5,6,3,2,1,4
5,6,3,2,1,4,7
5,2,3,6,8,1,4,7
5,2,3,6,8,9,1,4,7
5,2,3,6,10,8,9,1,4,7
5,2,3,6,10,11,8,9,1,4,7
5,2,3,6,10,11,12,8,9,1,4,7
5,2,3,6,10,13,11,12,8,9,1,4,7
5,2,3,6,10,13,11,14,12,8,9,1,4,7
5,2,3,6,10,13,11,14,12,8,15,9,1,4,7
3,14,12,16,8,15,9,4,7,5,6,2,10,11,13,1
17,3,14,12,16,8,15,9,4,7,5,6,2,10,11,13,1
18,17,3,14,12,16,8,15,9,4,7,5,6,2,10,11,13,1
18,17,3,19,14,12,16,8,15,9,4,7,5,6,2,10,11,13,1
18,17,3,19,14,12,16,8,15,9,4,7,5,6,2,10,11,13,20,1