Message-ID: <8615c983-1662-43b4-b0c9-49d194ac33aa@dunslane.net>
Date: Thu, 21 Aug 2025 11:47:30 -0400
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Subject: Re: Speed up COPY FROM text/CSV parsing using SIMD
To: Nazir Bilal Yavuz <byavuz81@gmail.com>, KAZAR Ayoub <ma_kazar@esi.dz>
Cc: Shinya Kato <shinya11.kato@gmail.com>, pgsql-hackers@postgresql.org
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From: Andrew Dunstan <andrew@dunslane.net>
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On 2025-08-19 Tu 10:14 AM, Nazir Bilal Yavuz wrote:
> Hi,
>
> On Tue, 19 Aug 2025 at 15:33, Nazir Bilal Yavuz <byavuz81@gmail.com> wrote:
>> I am able to reproduce the regression you mentioned but both
>> regressions are %20 on my end. I found that (by experimenting) SIMD
>> causes a regression if it advances less than 5 characters.
>>
>> So, I implemented a small heuristic. It works like that:
>>
>> - If advance < 5 -> insert a sleep penalty (n cycles).
> 'sleep' might be a poor word choice here. I meant skipping SIMD for n
> number of times.
>

I was thinking a bit about that this morning. I wonder if it might be 
better instead of having a constantly applied heuristic like this, it 
might be better to do a little extra accounting in the first, say, 1000 
lines of an input file, and if less than some portion of the input is 
found to be special characters then switch to the SIMD code. What that 
portion should be would need to be determined by some experimentation 
with a variety of typical workloads, but given your findings 20% seems 
like a good starting point.


cheers


andrew


--
Andrew Dunstan
EDB: https://www.enterprisedb.com