Michael Nguyen writes:
Each server is fairly busy and always has between 800-1900 simultaneous connections (mostly POP3). What type of settings would you guys recommend so that we can get this setup to a point where it can handle the same amount of users and connections?
You should determine the average length of a POP3 session, perhaps using courier-analog. Most of the POP3 connections will find an empty mailbox, so let's say that the average POP3 connection lasts ten seconds long.
With 800-1900 simultaneous connections, at any given time, that computes to a rough average of between 100 and 150 connections per second.
With the default five authdaemond processes running, that comes out to 20-30 authentication requests per second, per process.
Therefore, each authentication request should take no longer than, about, 30-50 milliseconds.
Each authentication request is, essentially, a single SQL query.
You should be able to run some benchmarks on your MySQL server and determine if 30-50 milliseconds is enough. If your MySQL takes longer than that, to respond to a query, the authentication requests will build up, and eventually time out.
If your MySQL server still has plenty of CPU cycles, and bandwidth, you can put them to use by increasing the number of authdaemond processes.
Of course, you'll need to rule out factors such as database locking, as contributing factors.
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