Horton

Re: Reduce timing overhead of EXPLAIN ANALYZE using rdtsc?

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: David Geier <geidav.pg@gmail.com>, vignesh C <vignesh21@gmail.com>, Lukas Fittl <lukas@fittl.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: 2023-01-17T13:46:12Z
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 →

  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

On Fri, Jan 13, 2023 at 2:56 PM Andres Freund <andres@anarazel.de> wrote:
> Does anybody see a reason to not move forward with this aspect? We do a fair
> amount of INSTR_TIME_ACCUM_DIFF() etc, and that gets a good bit cheaper by
> just using nanoseconds. We'd also save memory in BufferUsage (144-122 bytes),
> Instrumentation (16 bytes saved in Instrumentation itself, 32 via
> BufferUsage).

I read through 0001 and it seems basically fine to me. Comments:

1. pg_clock_gettime_ns() doesn't follow pgindent conventions.

2. I'm not entirely sure that the new .?S_PER_.?S macros are
worthwhile but maybe they are, and in any case I don't care very much.

3. I've always found 'struct timespec' to be pretty annoying
notationally, so I like the fact that this patch would reduce use of
it.

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