squirrelmail/plugins/filters/bulkquery/README

bulkquery - A program by Brent Bice - 02/2002

   Bulkquery is a multi-threaded program that makes a large number of
DNS queries as fast as possible. It's tailored for making DNS queries for
specific IP addresses against specific DNS based RBLs.

   "Why bother?"
I've been asked this several times. While running squirrelmail on a server
with very little bandwidth and very high latency (a dial-up account - snicker)
I noticed that while my filters plugin was making gethostbyname() function
calls, my dial-up line was mostly idle. This was, apparently, because all
the DNS function calls were being made in series. Once a DNS query had been
sent, no others were sent until a response had been received or until a 
certain timeout period had occurred.  And some of the RBLs were quite a
bit faster than the others.  This seemed pretty inefficient. "Why not make
more DNS queries while waiting for the replies," I thought.

   After several attempts to make a multi-threaded program to make the queries
using the standard DNS library calls, I realized why. The library functions
weren't thread-safe and most of the replies would be lost. Luckily, a
friend of a friend told me about the lwres API in Bind 9.x and told me that
IT was definitely thread-safe and very fast.

   Boy was SHE right!

   So, how much faster is it?  It will depend on your bandwidth and the
latency of your connection. But for those of us trying to make do with less,
bulkquery is a LOT faster.  On a dial-up connection, I can make queries
anywhere from 6 to 10 times faster!  On my T1 at work, the queries are
usually between 2 and 7 times faster. The bottom line of all of this is
that even on my T1 at work, the filters plugin can query ALL of the RBLs
for all the new email in my INBOX in less than half the time it takes using
the PHP gethostbyname() function calls.