I've been asked questions about a site that slows way down on occasion. This is a cloud-based server at Rackspace. Since Rackspace has a fairly good reputation, I am guessing they are not the real problem.
I looked at the database stats; it is using Qcache and the numbers look pretty decent.
What I do see that I question is that their notifications module (I forget which one): A) Writes to dblog (Watchdog) on every cron interval, even if it has nothing to do (I hate that). B) When there is a notification (pretty often), it writes a separate line for each one. C) Some of those notifications result in many (100 or more) emails. During one page refresh when I experienced the drastic slow down, this high volume email happened.
So I am wondering if these high-volume email sends can have a serious effect on performance? Since I assume the answer is yes, what can be done to lessen this impact? I see two main spots to work on: Watchdog usage and email load.
Nancy Injustice anywhere is a threat to justice everywhere. -- Dr. Martin L. King, Jr.