Couchdb can make a .compact file when the volume is almost out of disk
space and then crash before writing the header.
If you then clean some space and try to compact again, it won't ever work.
[Wed, 23 Jun 2010 16:11:59 GMT] [error] [emulator] Error in process
<0.1976.0> with exit value:
The presence of the invalid .compact file prevents it, and needs to be
Remedy: delete the .compact file if there is no valid header when _compact is called for the second time.