Re: [GENERAL] Runtime analysis

Neto pr <netoprbr9@gmail.com> writes:
> I expected that the first run would always take longer than the others
> because of not having cached data, but look what happened:
>    - in 6 cases the first execution was more faster than all executions.
>    - in 2 cases only, the first exececution was more slower than all
>    executions
> If anyone has any suspicion or explanation,  why in some cases the first
> execution can be faster than the others, please reply to this email.

Your Xeon is probably a variable-speed chip; did you take measures to
freeze the CPU frequency?  On my RHEL server, I generally can't get
very reproducible numbers from benchmarks unless I first do
"sudo cpupower frequency-set --governor performance"
because the default "ondemand" governor is too eager to ratchet down
the frequency.  Things might be different on Debian though.

In multi-socket servers, NUMA effects across sockets can be a big
headache too.
        regards, tom lane


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