| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Melanie Plageman <melanieplageman(at)gmail(dot)com> |
| Cc: | Alexander Korotkov <aekorotkov(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Pavel Borisov <pashkin(dot)elfe(at)gmail(dot)com>, Japin Li <japinli(at)hotmail(dot)com>, Mark Dilger <mark(dot)dilger(at)enterprisedb(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Michael Paquier <michael(at)paquier(dot)xyz>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Nazir Bilal Yavuz <byavuz81(at)gmail(dot)com> |
| Subject: | Re: Table AM Interface Enhancements |
| Date: | 2024-04-10 21:21:17 |
| Message-ID: | 20240410212117.mxsldz2w6htrl36v@awork3.anarazel.de |
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| Lists: | pgsql-hackers |
Hi,
On 2024-04-10 16:50:44 -0400, Melanie Plageman wrote:
> This brings up a question about the prefetching. We never had to have
> this discussion for sequential scan streaming read because it didn't
> (and still doesn't) do prefetching. But, if we push the streaming read
> code down into the heap AM layer, it will be doing the prefetching.
> So, do we remove the prefetching from acquire_sample_rows() and expect
> other table AMs to implement it themselves or use the streaming read
> API?
The prefetching added to acquire_sample_rows was quite narrowly tailored to
something heap-like - it pretty much required that block numbers to be 1:1
with the actual physical on-disk location for the specific AM. So I think
it's pretty much required for this to be pushed down.
Using a read stream is a few lines for something like this, so I'm not worried
about it. I guess we could have a default implementation for block based AMs,
similar what we have around table_block_parallelscan_*, but not sure it's
worth doing that, the complexity is much lower than in the
table_block_parallelscan_ case.
Greetings,
Andres
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