Re: Streaming read-ready sequential scan code

Hi,

On 2024-04-08 09:36:59 +1200, Thomas Munro wrote:
> I've been on the fence about that flag for sequential scan... Some
> days I want to consider changing to READ_STREAM_DEFAULT and relying on
> our "anti-heuristics" to suppress advice, which would work out the
> same in most cases but might occasionally win big.

Agreed, it's pretty easy to end up with a fairly "fragmented" set of a
relation's buffers in s_b. OTOH, there might not be any need for the
heuristic if we actually trigger reads asynchronously.

> BTW looking at the branching in read-stream user patches that have an
> initialisation step like yours, I wonder if it might every make sense
> to be able to change the callback on the fly from inside the callback,
> so that you finish up with a branchless one doing most of the work. I
> have no idea if it's worth it...

I was wondering about that too, I dislike those branches. But instead of
changing the callback, it seems like a better design would be to have another
dedicated callback for that? There already is a dedicated branch for the
"just starting up" path in read_stream_next_buffer(), so it'd be pretty much
free to call another callback there.

Greetings,

Andres Freund