>> 2) The other problem, which Q was incorrectly attributing
>> to the double-installation problem, was that record in the
>> database was corrupted (I think) so that it could not be
>> decompressed.  I don't know the reason for the corrupt record.
>> I think qwitter might be using one connection from multiple threads,
>> and if so, I think that could be the reason.

A quick look at the qwitter source code makes me think that they
are using Durus instances from the same Connection in multiple
threads.  Durus does not support that usage pattern.