Re: Skip prefetch for block references that follow a FPW or WILL_INIT of the same block

Hi Jeremy,

I feel a little bit confused, could you please share more about the
following?

> Vacuum is the more concerning case here, as large vacuums would
consistently
> cause the 16x IOPS amplification on replicas.

I did not find a 16x amplification diagram in your github link. Maybe I am
missing
something?

> I also think that visibility map and FSM reads were the largest cause of
> replica reads when prefetch was disabled

In my understanding, these forks are quite small. VM is 1/4000 and most of
them
are constantly in memory, so not lots of IO required? For FSM, I dont think
they are
WAL logged and therefore they can not be recovery prefetched.

Additionally, most EBS-like block storage services offer a high
IOPS-to-throughput
ratio(usually 1:16-32kb), aggressive prefetching may not incur significant
waste.

This extra throughput capacity would likely go underutilized, especially
it is running heavy sequential scan prefetching.

Thanks,
Shihao