Re: index prefetching

On 18/01/2024 6:00 pm, Tomas Vondra wrote:
> On 1/17/24 09:45, Konstantin Knizhnik wrote:
>> I have integrated your prefetch patch in Neon and it actually works!
>> Moreover, I combined it with prefetch of leaf pages for IOS and it also
>> seems to work.
>>
> Cool! And do you think this is the right design/way to do this?

I like the idea of prefetching TIDs in executor.

But looking though your patch I have some questions:

1. Why it is necessary to allocate and store all_visible flag in data
buffer. Why caller of  IndexPrefetchNext can not look at prefetch field?

+        /* store the all_visible flag in the private part of the entry */
+        entry->data = palloc(sizeof(bool));
+        *(bool *) entry->data = all_visible;

2. Names of the functions `IndexPrefetchNext` and
`IndexOnlyPrefetchNext` are IMHO confusing because they look similar and
one can assume that for one is used for normal index scan and last one -
for index only scan. But actually `IndexOnlyPrefetchNext` is callback
and `IndexPrefetchNext` is used in both nodeIndexscan.c and
nodeIndexonlyscan.c