Re: index prefetching

On 8/29/25 01:57, Peter Geoghegan wrote:
> On Thu, Aug 28, 2025 at 7:52 PM Tomas Vondra <tomas(at)vondra(dot)me> wrote:
>> Use this branch:
>>
>> https://github.com/tvondra/postgres/commits/index-prefetch-master/
>>
>> and then Thomas' patch that increases the prefetch distance:
>>
>>
>> https://www.postgresql.org/message-id/CA%2BhUKGL2PhFyDoqrHefqasOnaXhSg48t1phs3VM8BAdrZqKZkw%40mail.gmail.com
>>
>> (IIRC there's a trivial conflict in read_stream_reset.).
>
> I found it quite hard to apply Thomas' patch. There's actually 3
> patches, with 2 earlier patches needed for earlier in the thread. And,
> there were significant merge conflicts to work around.
>

I don't think the 2 earlier patches are needed, I only ever applied the
one in the linked message. But you're right there were more merge
conflicts, I forgot about that. Here's a patch that should apply on top
of the prefetch branch.

> I'm not sure that Thomas'/your patch to ameliorate the problem on the
> read stream side is essential here. Perhaps Andres can just take a
> look at the test case + feature branch, without the extra patches.
> That way he'll be able to see whatever the immediate problem is, which
> might be all we need.
>

AFAICS Andres was interested in reproducing the regression with an
increased distance. Or maybe I got it wrong.

regards

--
Tomas Vondra