I would like to find some analysis (published work, blog posts) on the overheads affiliated with the guarantees provided by MVCC isolation. More specifically, assuming the current workload is CPU bound (as opposed to IO) what is the CPU overhead of generating the WAL, the overhead of version checking and version creation, and of garbage collecting old and unnecessary versions? For what it’s worth, I am working on a research project where it is envisioned that some of this work can be offloaded.
MVCC is a benefit, not an overhead. To understand that you should compare MVCC with a system that performs S2PL.
If you're thinking that somehow consistency isn't important, I'd hope that you also consider some way to evaluate the costs associated with inconsistent and incorrect results in applications, or other architectural restrictions imposed to make that possible. It's easy to make assumptions in the lab that don't work in the real world.
--
Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
