Are you hosting a static site or dynamic?
According to support, your memory usage is probably related to simultaneous apache handler threads that are spawned to handle traffic on your site.
I'm not sure what your question is. I think everyone has "traffic spikes" during the day but that PS handles it fine in most cases but just not yours for some reason that you're currently investigating.
In my mind, PS is all about being able to reserve the exact amount of dedicated resources to handle your own site. Assuming you do that, your site will be rock solid and not affected by the other users who are sharing your physical server.
Unfortunately, if you reserve "less" memory than your sites need, it becomes very, very obvious and your site is limited/throttled (effectively) in order to protect the other users on your physical server.
The reason dreamhost suspects bots is because bots can cause steep traffic spikes. And by traffic spikes I mean that they can issue hundreds of requests virtually instantaneously. Obviously, even if each request is handled in less than a second but the bot issues 100 requests simultaneously to your site, your apache is going to spawn 100 handlers and try to suck up 1GB of memory. This memory request will fail.
Unkind bots are hell on your site.
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