[Twisted-web] what are the advantage of using a single-threaded server? and when should we use deferreds?

inhahe inhahe at gmail.com
Sat Apr 26 02:44:54 EDT 2008

hi, excuse my noobness, I have a few basic questions about twisted, or
probably about web servers in general.

what is the advantage of using a single-threaded server?

i figured it makes it more scalable because there's too much overhead to
have a thread for each user when you have many simultaneous users.  but a
friend i'm talking to now says that using i/o blocking threads is perfectly
scalable for a large number of simultaneous users.

if that's true i can only see a disadvantage in using a single-threaded
server -- having to use deferreds and stuff to make things asynchronous

i also don't understand how you're supposed to use deferreds
the twisted doc says deferreds won't *make* your code asynchronous.  so
let's say you have to do an sql query that takes 10 seconds, deferreds would
be useless for making that not block unless you have a way of making that
sql query non-blocking already?  how is that done?  do you run a separate
thread of your own for each sql query?  one thread for all sql queries?

also I wonder in an typical twisted app, just how slow should an operation
be before you use a deferred?  what if a user enters a username and password
and i have to look that up in the database. do i use a deferred?  just how
bad should the query be before using a deferred?

(reading the twisted docs is like reading a brick wall for me, it would be
nice if someone could just explain things to me in simple terms.)

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