This kind of benchmarking should really be run on physical hardware where you know that the underlying resources are not being switched out. The repeated runnin

This kind of benchmarking should really be run on physical hardware where you know that the underlying resources are not being switched out. The repeated running somewhat mitigates this, but when you don't control the hardware, decisions are being made that are beyond your visibility. The almost 50% more context switches for normal Postgres is very telling. If those had any disk implication which is quite possible with the 512Mb of RAM, it could easily explain the discrepancy.