We do parallelism across CPUs and nodes. We run single-threaded to get the most out of a CPU in a shared-nothing architecture. Many single-threaded apps aren't

We do parallelism across CPUs and nodes. We run single-threaded to get the most out of a CPU in a shared-nothing architecture. Many single-threaded apps aren't written to really take advantage of all a CPU has to offer. But there are also prices to pay to run multi-threaded; context switches, etc.