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

On Mon, Oct 26, 2026 at 10:58 PM Jeremy Schneider <schneider(at)ardentperf(dot)com>
wrote:

> I'm doing some more testing, and seeing if I can also simplify the
> reproduction by using two local cgroups instead of two VMs that need
> separate disks. I'm also toying with a patch locally to add io_uring to
> Tomas' patches, we'll see how far I get.
>

This works well for a minimal local repro:
1. systemd-run -p MemoryMax=256M -p MemorySwapMax=0 -p IOAccounting=yes
2. scale-40 pgbench (500 MB accounts table)
3. UPDATE pgbench_accounts SET abalance = abalance + 1 WHERE aid % 20 = 0

https://github.com/ardentperf-labs/walreceiver-outage-repro/tree/main/local/prefetch

The read IOPS amplification is very pronounced, even in the case of FPI
disabled (which is the case that we want replica prefetch for).

These ran on my laptop, a Dell XPS 14 with an NVMe SSD. Each numeric cell:
run1 / run2 / run3.
MB is decimal; mean read size is in KiB.

recovery_prefetch=try, full_page_writes=off

Run 1 Run 2 Run 3
Read MB Primary 1,008 912 865
Replica 677 745 738
Read ops Primary 7,435 5,781 3,294
Replica 29,524 52,955 29,008
Mean KiB Primary 132 154 256
Replica 22 14 25

recovery_prefetch=off, full_page_writes=off

Run 1 Run 2 Run 3
Read MB Primary 1,072 828 788
Replica 770 949 781
Read ops Primary 7,445 1,954 2,988
Replica 380 1,664 901
Mean KiB Primary 141 414 257
Replica 1,978 557 847

recovery_prefetch=try, full_page_writes=on

Run 1 Run 2 Run 3
Read MB Primary 1,929 1,795 1,556
Replica 600 858 662
Read ops Primary 5,835 3,797 4,846
Replica 71,617 75,289 75,686
Mean KiB Primary 323 462 314
Replica 8 11 9

recovery_prefetch=off, full_page_writes=on

Run 1 Run 2 Run 3
Read MB Primary 2,221 1,815 1,765
Replica 12 108 2
Read ops Primary 4,626 2,992 11,768
Replica 104 417 53
Mean KiB Primary 469 592 146
Replica 114 254 42