My analytics table has 190M rows, about 150GB ins size.
Storage engine is MyISAM with 

```
key-buffer-size=16G
myisam_sort_buffer_size=2G
myisam-max-sort-file-size=200G.

```

Machine has 32GB memory.
While creating 10 simple indexes (no covering, no prefix, just column names using BTREE) I noticed:

* first index - 40 minutes
* second index - 50 minutes
* ...
* fifth index - 2 hours
* eleventh index - 3 1/2 hours

Each index adds between 1GB and 3GB to the .myi file.
Has anybody experienced a similar increase in run-time? Is there any way to get the performance of the first index creation for the other indexes?