Re: Reduce timing overhead of EXPLAIN ANALYZE using rdtsc?

Tomas Vondra <tomas.vondra@enterprisedb.com>

From: Tomas Vondra <tomas.vondra@enterprisedb.com>

To: David Geier <geidav.pg@gmail.com>, vignesh C <vignesh21@gmail.com>

Cc: Lukas Fittl <lukas@fittl.com>, Michael Paquier <michael@paquier.xyz>, Ibrar Ahmed <ibrar.ahmad@gmail.com>, Maciek Sakrejda <m.sakrejda@gmail.com>, Andres Freund <andres@anarazel.de>, pgsql-hackers <pgsql-hackers@postgresql.org>

Date: 2023-01-16T20:34:42Z

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

Hi,

there's minor bitrot in the Mkvcbuild.pm change, making cfbot unhappy.

As for the patch, I don't have much comments. I'm wondering if it'd be
useful to indicate which timing source was actually used for EXPLAIN
ANALYZE, say something like:

 Planning time: 0.197 ms
 Execution time: 0.225 ms
 Timing source: clock_gettime (or tsc)

There has been a proposal to expose this as a GUC (or perhaps as explain
option), to allow users to pick what timing source to use. I wouldn't go
that far - AFAICS is this is meant to be universally better when
available. But knowing which source was used seems useful.


regards

-- 
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company