Horton

Re: Reduce timing overhead of EXPLAIN ANALYZE using rdtsc?

Álvaro Herrera <alvherre@kurilemu.de>

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From: Álvaro Herrera <alvherre@kurilemu.de>
To: Lukas Fittl <lukas@fittl.com>
Cc: Andres Freund <andres@anarazel.de>, pgsql-hackers <pgsql-hackers@postgresql.org>, David Geier <geidav.pg@gmail.com>, Pavel Stehule <pavel.stehule@gmail.com>, vignesh C <vignesh21@gmail.com>, Michael Paquier <michael@paquier.xyz>, Ibrar Ahmed <ibrar.ahmad@gmail.com>, Maciek Sakrejda <m.sakrejda@gmail.com>, Tomas Vondra <tomas@vondra.me>
Date: 2025-10-19T18:16:20Z
Lists: pgsql-hackers

Commits

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  1. pg_test_timing: Also test RDTSC[P] timing, report time source, TSC frequency

  2. Allow retrieving x86 TSC frequency/flags from CPUID

  3. instrumentation: Standardize ticks to nanosecond conversion method

  4. instrumentation: Use Time-Stamp Counter on x86-64 to lower overhead

  5. Zero initialize uses of instr_time about to trigger compiler warnings

  6. instr_time: Represent time as an int64 on all platforms

  7. Add 250c8ee07ed to git-blame-ignore-revs

Attachments

On 2025-Jul-27, Lukas Fittl wrote:

> See attached v11 (and moved to the PG19-2 commitfest), split into a new set
> of patches:

I rebased (but not reviewed) this patchset now that Michael committed
part of 0001, as seen in another thread.

Quickly looking at 0003, I wonder if adding a separate --fast switch to
pg_test_timing is really what we want.  Why not report both the fast and
legacy measurements in platforms that support both, instead?  If I were
a consultant trying to understand a customer's system, I would have to
ask them to run it twice just in case 'fast' is supported, and I don't
think that's very helpful.  Also, were the doc updates lost somehow, or
were they made irrelevant by other concurrent pg_test_timing
development?

Thanks

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
"Ninguna manada de bestias tiene una voz tan horrible como la humana" (Orual)