Hi, On 2019-12-16 17:48:16 -0500, Tom Lane wrote: > Hmm, that's an interesting thought. The OP did say the CPU type, > but according to Intel's spec page for it [1] the difference between > base and turbo frequency is only 4.0 vs 4.2 GHz, which doesn't seem > like enough to explain the results ... unless you suppose it actually > throttled to below base freq, which surely shouldn't happen that fast. > Might be worth watching the CPU frequency while doing the test though. FWIW, it takes about 3s for my laptop CPU to throttle way below non-turbo when I put it under strenuous load. Obviously that's a laptop, and caused by a firmware bug leading to fans not spinning fast enough automatically. But it'd not take that much for insufficient cooling to cause problems in a desktop either. Been there, done that. But: I don't see that causing a 10x slowdown as reported in the first mail in this thread. I think we need a system-wide perf profile during a few initial "good" runs and then later from a few "really bad" runs. For that you'd have to make sure you compiled postgres with debug symbols (--enable-debug to configure), and then run something like perf record -o fast.data --call-graph dwarf -a sleep 3 while running repeated "fast" queries and then perf record -o slow.data --call-graph dwarf -a sleep 3 and then show us the results of something like perf report -i fast.data -g folded --percent-limit 1 > fast.txt perf report -i slow.data -g folded --percent-limit 1 > slow.txt and also, if your perf is new enough: perf diff fast.data slow.data > diff.txt - Andres
