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help / color / mirror / Atom feedFrom: Nathan Bossart <[email protected]>
To: KAZAR Ayoub <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: Pg Hackers <[email protected]>
Cc: Neil Conway <[email protected]>
Cc: Manni Wood <[email protected]>
Cc: Andrew Dunstan <[email protected]>
Cc: Shinya Kato <[email protected]>
Cc: Mark Wong <[email protected]>
Cc: Nazir Bilal Yavuz <[email protected]>
Subject: Re: Speed up COPY TO text/CSV parsing using SIMD
Date: Thu, 26 Mar 2026 16:23:48 -0500
Message-ID: <acWj5FntidHJ9nVP@nathan> (raw)
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On Wed, Mar 18, 2026 at 03:29:32AM +0100, KAZAR Ayoub wrote:
> If we have some json(b) column like : {"key1":"val1","key2":"val2"}, for
> CSV format this would immediately exit the SIMD path because of quote
> character, for json(b) this is going to be always the case.
> I measured the overhead of exiting the SIMD path a lot (8 million times for
> one COPY TO command), i only found 3% regression for this case, sometimes
> 2%.
I'm a little worried that we might be dismissing small-yet-measurable
regressions for extremely common workloads. Unlike the COPY FROM work,
this operates on a per-attribute level, meaning we only use SIMD when an
attribute is at least 16 bytes. The extra branching for each attribute
might not be something we can just ignore.
> For cases where we do a false commitment on SIMD because we read a binary
> size >= sizeof(Vector8), which i found very niche too, the short circuit to
> scalar each time is even more negligible (the above CSV JSON case is the
> absolute worst case).
That's good to hear.
--
nathan
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Subject: Re: Speed up COPY TO text/CSV parsing using SIMD
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