Re: PoC: prefetching index leaf pages (for inserts)

On Mon, 6 Nov 2023 at 22:36, Tomas Vondra <tomas.vondra@enterprisedb.com> wrote:
>
> Seems cfbot was not entirely happy about the patch, for two reasons:
>
> 1) enable_insert_prefetching definition was inconsistent (different
> boot/default values, missing in .conf and so on)
>
> 2) stupid bug in execReplication, inserting index entries twice
>
> The attached v3 should fix all of that, I believe.
>
>
> As for the path forward, I think the prefetching is demonstrably
> beneficial. There are cases where it can't help or even harms
> performance. I think the success depends on three areas:
>
> (a) reducing the costs of the prefetching - For example right now we
> build the index tuples twice (once for prefetch, once for the insert),
> but maybe there's a way to do that only once? There are also predicate
> indexes, and so on.
>
> (b) being smarter about when to prefetch - For example if we only have
> one "prefetchable" index, it's somewhat pointless to prefetch (for
> single-row cases). And so on.
>
> (c) not prefetching when already cached - This is somewhat related to
> the previous case, but perhaps it'd be cheaper to first check if the
> data is already cached. For shared buffers it should not be difficult,
> for page cache we could use preadv2 with RWF_NOWAIT flag. The question
> is if this is cheap enough to be cheaper than just doing posix_fadvise
> (which however only deals with shared buffers).

CFBot shows that the patch does not apply anymore as in [1]:
=== Applying patches on top of PostgreSQL commit ID
7014c9a4bba2d1b67d60687afb5b2091c1d07f73 ===
=== applying patch ./0001-insert-prefetch-v3.patch
patching file src/backend/access/brin/brin.c
Hunk #1 FAILED at 117.
1 out of 1 hunk FAILED -- saving rejects to file
src/backend/access/brin/brin.c.rej
patching file src/backend/access/gin/ginutil.c
Hunk #1 FAILED at 64.
1 out of 1 hunk FAILED -- saving rejects to file
src/backend/access/gin/ginutil.c.rej
patching file src/backend/access/gist/gist.c
Hunk #1 FAILED at 86.
1 out of 1 hunk FAILED -- saving rejects to file
src/backend/access/gist/gist.c.rej
patching file src/backend/access/hash/hash.c
Hunk #1 FAILED at 83.
1 out of 1 hunk FAILED -- saving rejects to file
src/backend/access/hash/hash.c.rej

Please post an updated version for the same.

[1] - http://cfbot.cputube.org/patch_46_4622.log

Regards,
Vignesh