Recommended number of threads? (in CPython)

mk mrkafk at
Thu Oct 29 16:56:42 CET 2009

Hello everyone,

I wrote run-of-the-mill program for concurrent execution of ssh command 
over a large number of hosts. (someone may ask why reinvent the wheel 
when there's pssh and shmux around -- I'm not happy with working details 
and lack of some options in either program)

The program has a working queue of threads so that no more than 
maxthreads number are created and working at particular time.

But this begs the question: what is the recommended number of threads 
working concurrently? If it's dependent on task, the task is: open ssh 
connection, execute command (then the main thread loops over the queue 
and if the thread is finished, it closes ssh connection and does .join() 
on the thread)

I found that when using more than several hundred threads causes weird 
exceptions to be thrown *sometimes* (rarely actually, but it happens 
from time to time). Although that might be dependent on modules used in 
threads (I'm using paramiko, which is claimed to be thread safe).

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