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Re: Reduce timing overhead of EXPLAIN ANALYZE using rdtsc?

David Geier <geidav.pg@gmail.com>

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From: David Geier <geidav.pg@gmail.com>
To: Andres Freund <andres@anarazel.de>, Jakub Wartak <jakub.wartak@enterprisedb.com>
Cc: Lukas Fittl <lukas@fittl.com>, Hannu Krosing <hannuk@google.com>, Robert Haas <robertmhaas@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>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2026-02-04T10:09:32Z
Lists: pgsql-hackers 
On 03.02.2026 18:44, Andres Freund wrote:
> Yea, I doubt this is the right path... Particularly because I really think we
> ought to eventually use this not just on linux but other OSs as well.

+1

>> BTW, -1 to fast_clock_source, +1 to clock_source or maybe
>> explain_clock_source(?)
> 
> Hm. I think it'd make sense to use eventually use this clock source for other
> timing tasks too, not just explain.  E.g. pg_stat_statements could benefit
> quite a bit from reducing the timing overhead.
> 
> Whereas it'll not make sense for anything that needs wall clock times - which
> imo makes a "clock_source" GUC misnamed.  Maybe "clock_source_timing" or such?

Makes sense. clock_source_timing works for me, or maybe easier to read
would be timing_clock_source. But doesn't matter much.

--
David Geier

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. pg_test_timing: Show additional TSC clock source debug info

  2. instrumentation: Avoid CPUID 0x15/0x16 for Hypervisor TSC frequency

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

  4. Allow retrieving x86 TSC frequency/flags from CPUID

  5. instrumentation: Standardize ticks to nanosecond conversion method

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

  7. Check for __cpuidex and __get_cpuid_count separately

  8. pg_test_timing: Reduce per-loop overhead

  9. Refactor handling of x86 CPUID instructions

  10. instrumentation: Drop INSTR_TIME_SET_CURRENT_LAZY macro

  11. Rename pg_crc32c_sse42_choose.c for general purpose

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

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

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