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Re: Reduce timing overhead of EXPLAIN ANALYZE using rdtsc?

Zsolt Parragi <zsolt.parragi@percona.com>

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From: Zsolt Parragi <zsolt.parragi@percona.com>
To: Lukas Fittl <lukas@fittl.com>
Cc: Andres Freund <andres@anarazel.de>, John Naylor <johncnaylorls@gmail.com>, Jakub Wartak <jakub.wartak@enterprisedb.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>, David Geier <geidav.pg@gmail.com>
Date: 2026-03-12T21:55:02Z
Lists: pgsql-hackers 
> Were you
> thinking of user-facing documentation, or more on the code side?

I'm not 100% sure, maybe code side is enough. With the current patch,
the behavior is only visible if somebody intentionally tries to make
it visible, and even then it's not really harmful.

In the code it's definitely worth mentioning since it's not trivial,
and stating it also makes it clear that it's not a bug/oversight. It
could be also useful info if another patch later wants to also use
timing_clock_source to keep in mind that users can change it
dynamically.

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