Thread

Re: Reduce timing overhead of EXPLAIN ANALYZE using rdtsc?

Lukas Fittl <lukas@fittl.com> — 2023-01-02T19:50:04Z

Hi David,

Thanks for continuing to work on this patch, and my apologies for silence
on the patch.

Its been hard to make time, and especially so because I typically develop
on an ARM-based macOS system where I can't test this directly - hence my
tests with virtualized EC2 instances, where I ran into the timing oddities.

On Mon, Jan 2, 2023 at 5:28 AM David Geier <geidav.pg@gmail.com> wrote:

> The INSTR_TIME_GET_MICROSEC() returns a uint64 while the other variants
> return double. This seems error prone. What about renaming the function
> or also have the function return a double and cast where necessary at
> the call site?
>

Minor note, but in my understanding using a uint64 (where we can) is faster
for any simple arithmetic we do with the values.


> If no one objects I would also re-register this patch in the commit fest.
>

+1, and feel free to carry this patch forward - I'll try to make an effort
to review my earlier testing issues again, as well as your later
improvements to the patch.

Also, FYI, I just posted an alternate idea for speeding up EXPLAIN ANALYZE
with timing over in [0], using a sampling-based approach to reduce the
timing overhead.

[0]:
https://www.postgresql.org/message-id/CAP53PkxXMk0j-%2B0%3DYwRti2pFR5UB2Gu4v2Oyk8hhZS0DRART6g%40mail.gmail.com

Thanks,
Lukas

-- 
Lukas Fittl