I need to test a saas service load by sending 1000s requests/sec from multiple remote sources. The urls need to be from my access log. Is there a service that does that?
You can replay a log with httperf
Here are some instructions: http://dekoder.wordpress.com/2010/11/23/replay-traffic-with-httperf/
Apachebench ("ab") can read urls from files, but you'd have to process the access logs first.
Check out these for distributed testing:
No longer developed: http://www.slamd.com/