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11-07-01
The DBIAgent is your answer to non-blocking DBI in POE.
This module was written because I was developing a system that was
bogging down at ONLY 1 million hits/day on dual 1GHz processors.
That's only 11.5 requests/second! Needless to say, it was obvious
that something wasn't working right.
After much sweat, research, and profiling, I noticed an odd thing:
Sometimes, my per-request times were in the milliseconds. Other
times, it was taking over 25 seconds to answer a single request. The
difference? DBI. During the times that my response times sucked, POE
was blocking on a DBI request. I was actually serving my requests,
all code considered, in milliseconds. But in the steps between
assembling the response and delivering it, my program was stuck in a
state that was making a DBI call, and waiting for the response.
The answer? FORK! Or, more specifically, use POE's facility for
forking off child processes to handle long-running tasks while the
main program continues to cycle between states: Wheel::Run.
DBIAgent forks off a configurable number of helper processes for
running DBI queries. The states that depend on the output of the
queries only get called when there is data for them to process. No
more agonizing about query optimization in terms of milliseconds
because the rest of your program will suffer. Leave that to the
operating system! POE is designed for doing a lot of things
concurrently. Waiting isn't doing, it's waiting... :-)
This module will ONLY work in the places where POE::Wheel::Run will
work. This generally means, *nix. Meaning, not on Windows (yet).
I can't take most of the credit for this module. Fletch
(fletch@fletch@phydeaux.org) had already done alot of this, and
contributed the skeleton code for the Helper module. The Queue module
is 99.6% his. I just packaged it up and wrote docs... (*his* was tied
into his program... *I* made distributable. :-)
Rob Bloodgood <rob@exitexchange.com>
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