Horton

Re: define pg_structiszero(addr, s, r)

Heikki Linnakangas <hlinnaka@iki.fi>

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From: Heikki Linnakangas <hlinnaka@iki.fi>
To: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Peter Smith <smithpb2250@gmail.com>
Cc: Peter Eisentraut <peter@eisentraut.org>, pgsql-hackers@lists.postgresql.org
Date: 2024-10-29T09:39:03Z
Lists: pgsql-hackers 
On 29/10/2024 09:54, Bertrand Drouvot wrote:
>> https://godbolt.org/z/x9hPWjheq.
> 
> Yeah, I also think that's fine. Peter Smith did some testing in [1] comparing
> memcmp and simple loop checking (thanks Peter for the testing!):
> 
> "
> Iterate 1000000 times...
> check zeros using loop -- elapsed=0.041196s
> check zeros using memcmp -- elapsed=0.016407s
> "
> 
> So, in this test, the loop is 0.024789s longer means 0.024789s/1000000=24 Nanosecond
> slower per comparison (If my math is correct).

I believe that test program is bogus. Look at the assembly code; the 
compiler optimized away the loops.

-- 
Heikki Linnakangas
Neon (https://neon.tech)

Commits

  1. Use pg_memory_is_all_zeros() in PageIsVerifiedExtended()

  2. Optimize pg_memory_is_all_zeros() in memutils.h

  3. Remove use of pg_memory_is_all_zeros() in bufpage.c

  4. Add pg_memory_is_all_zeros() in memutils.h