Re: Reduce timing overhead of EXPLAIN ANALYZE using rdtsc?

Robert Haas <robertmhaas@gmail.com>

From: Robert Haas <robertmhaas@gmail.com>

To: Lukas Fittl <lukas@fittl.com>

Cc: David Geier <geidav.pg@gmail.com>, Andres Freund <andres@anarazel.de>, 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: 2025-11-19T19:36:53Z

Lists: pgsql-hackers

Commits

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

pg_test_timing: Also test RDTSC[P] timing, report time source, TSC frequency
- 16fca4825483 19 (unreleased) landed
Allow retrieving x86 TSC frequency/flags from CPUID
- bcb2cf41f964 19 (unreleased) landed
instrumentation: Standardize ticks to nanosecond conversion method
- 0022622c93d9 19 (unreleased) landed
instrumentation: Use Time-Stamp Counter on x86-64 to lower overhead
- 294520c44487 19 (unreleased) landed
Zero initialize uses of instr_time about to trigger compiler warnings
- 25b2aba0c3a5 16.0 landed
instr_time: Represent time as an int64 on all platforms
- 03023a2664f8 16.0 landed
Add 250c8ee07ed to git-blame-ignore-revs
- ff23b592ad66 16.0 cited

On Wed, Nov 19, 2025 at 11:55 AM Lukas Fittl <lukas@fittl.com> wrote:
> Overall, I'm still thinking a GUC might be the way to go, but I don't think anyone else was enthusiastic about that idea :)

Reliable feature auto-detection is the best option, but if that's not
possible, I think the choices are add a GUC or give up on the project
altogether. Using a GUC to deal with platform dependencies is a pretty
reasonable concept -- see, e.g. dynamic_shared_memory_type or
huge_pages or io_method. If we can't autodetect it reliably and we
aren't willing to add a GUC, we're basically saying there's not enough
value here to justify adding a configuration parameter. That's often a
totally reasonable conclusion -- it can easily happen that the
benefits of a platform-specific optimization are too small to make it
worth configuring. But I would have thought that in this case the
benefits might be quite large.

-- 
Robert Haas
EDB: http://www.enterprisedb.com