What does the mdbox_rotate_size influence?

[Marc Roos]

I wondered why mdbox_rotate_size is 2MB by default.

I thought if I increased it to 16MB, maybe there would be less disk io, 
but I dont see any difference. Furthermore I read in some thread that 
increasing it from 2MB, could give problems when deleting messages, can 
someone explain this?

Does anyone have this on a cephfs mount, does it make sense to set this 
to 4MB?


[@test2 ~]# pr -m -t mail04-mdbox-vdb-append-64kb-4MB-6.log 
mail04-mdbox-vdb-append-64kb-16MB-7.log |less
Logi Sele Appe                      Logi Sele Appe
100% 100% 100%                      100% 100% 100%
   1    1    6   1/  1                 1    1    8   1/  1
   0    0    9   1/  1                 0    0    9   1/  1
   0    0    7   1/  1                 0    0    7   1/  1
   0    0   10   1/  1                 0    0    8   1/  1
   0    0    7   1/  1                 0    0   10   1/  1
   0    0    8   1/  1                 0    0    9   1/  1
   0    0    9   1/  1                 0    0   10   1/  1
   0    0   10   1/  1                 0    0    9   1/  1
   0    0    9   1/  1                 0    0    7   1/  1
   0    0   11   1/  1                 0    0    8   1/  1
  29    3 1093 ms/cmd avg             37    1 1110 ms/cmd avg
Logi Sele Appe                      Logi Sele Appe
100% 100% 100%                      100% 100% 100%
   0    0   10   1/  1                 0    0    8   1/  1
   0    0    9   1/  1                 0    0    8   1/  1
   0    0   10   1/  1                 0    0   10   1/  1
   0    0    9   1/  1                 0    0   10   1/  1
   0    0   11   1/  1                 0    0    8   1/  1
   0    0    9   1/  1                 0    0    9   1/  1
   0    0    8   1/  1                 0    0    6   1/  1
   0    0   11   1/  1                 0    0    9   1/  1
   0    0    9   1/  1                 0    0    7   1/  1
   0    0    9   1/  1                 0    0    9   1/  1
   0    0 1063 ms/cmd avg              0    0 1202 ms/cmd avg
Logi Sele Appe                      Logi Sele Appe
100% 100% 100%                      100% 100% 100%
   0    0    8   1/  1                 0    0    8   1/  1
   0    0   10   1/  1                 0    0   10   1/  1
   0    0    7   1/  1                 0    0   11   1/  1
   0    0   10   1/  1                 0    0   10   1/  1
   0    0   10   1/  1                 0    0   10   1/  1
   0    0   11   1/  1                 0    0    9   1/  1
   0    0    7   1/  1                 0    0    8   1/  1
   0    0   11   1/  1                 0    0    9   1/  1
   0    0    8   1/  1                 0    0   10   1/  1
   0    0   10   1/  1                 0    0    7   1/  1
   0    0 1077 ms/cmd avg              0    0 1060 ms/cmd avg
Logi Sele Appe                      Logi Sele Appe
100% 100% 100%                      100% 100% 100%
   0    0    7   1/  1                 0    0    9   1/  1
   0    0    9   1/  1                 0    0   10   1/  1
   0    0    6   1/  1                 0    0    6   1/  1
   0    0    9   1/  1                 0    0    7   1/  1
   0    0    8   1/  1                 0    0    9   1/  1
   0    0   10   1/  1                 0    0   10   1/  1
   0    0    9   1/  1                 0    0    9   1/  1
   0    0    7   1/  1                 0    0   10   1/  1
   0    0    9   1/  1                 0    0    9   1/  1
   0    0    7   1/  1                 0    0    9   1/  1
   0    0 1246 ms/cmd avg              0    0 1138 ms/cmd avg
...
...
...
...
   0    0    8   1/  1                 0    0    9   1/  1
   0    0    6   1/  1                 0    0    8   1/  1
   0    0    6   1/  1                 0    0    7   1/  1
   0    0    7   1/  1                 0    0    8   1/  1
   0    0    5   1/  1                 0    0    9   1/  1
   0    0    5   1/  1                 0    0   10   1/  1
   0    0    6   1/  1                 0    0   11   1/  1
   0    0    7   1/  1                 0    0    9   1/  1
   0    0    6   1/  1                 0    0    9   1/  1
   0    0    7   1/  1                 0    0   10   1/  1
   0    0 1596 ms/cmd avg              0    0 1126 ms/cmd avg
Logi Sele Appe                      Logi Sele Appe
100% 100% 100%                      100% 100% 100%
   0    0    7   1/  1                 0    0    8   1/  1
   0    0 1583 ms/cmd avg              0    0 1140 ms/cmd avg

Totals:                             Totals:
Logi Sele Appe                      Logi Sele Appe
100% 100% 100%                      100% 100% 100%
   1    1 1978                         1    1 2021