all python threads hung

I have a number of threads which collect and queue data.  A separate 
thread inserts the queued data in to an sqlite database.  Another thread 
services network requests for statics from the database.

The problem I have is long periods of time where all threads in the app 
appear to be hung. I've found that the duration of the 'stall' is always 
a multiple of the pysqlite timeout I've set -- typically 2x or 3x.  My 
timeout was set to 20seconds, but none of the database transactions are 
longer than 200ms.

At most, I'd expect my two threads to hang.  I'm not understanding how 
all the threads in the system could be effected.  Any thoughts would be 
greatly appreciated.