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From: John Naylor <[email protected]>
To: David Geier <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: Peter Geoghegan <[email protected]>
Subject: Re: tuple radix sort
Date: Thu, 13 Nov 2025 11:01:18 +0700
Message-ID: <CANWCAZbwX5wb+pCU8hTQYonDAqBhQt5ZH7EP8cQL7O107fYoKg@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <CANWCAZYzx7a7E9AY16Jt_U3+GVKDADfgApZ-42SYNiig8dTnFA@mail.gmail.com>
	<[email protected]>

On Wed, Nov 12, 2025 at 9:28 PM David Geier <[email protected]> wrote:
> I've also been looking into radix sort the last days to accelerate GIN
> index builds. Ordering and removing duplicates requires a fast sort in
> generate_trgm().

If that's the case then I suggest first seeing if dfd8e6c73ee made
things any worse. A simpler possible improvement is to use a similar
normalization step for the chars, if needed, then do the sort and
quinique with a specialization for unsigned chars. (We don't yet
specialize qunique, but that can be remedied). If you're interested,
please start a separate thread for that.

> What would be great is if we could build a generic radix sort
> implementation, similarly to sort_template.h that can be used in other
> places. We would have to think a bit about the interface because instead
> of a comparator we would require some radix extraction callback.

That's moving the goalposts too far IMO. I want to get to a place
where I feel comfortable with the decisions made, and that already
requires a lot of testing. Also, I don't want to risk introducing
abstractions that make future improvements to tuplesort more
cumbersome.

--
John Naylor
Amazon Web Services

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