Re: Clear empty space in a page.

Hi,

I happened to be running some postgres on zfs on Linux/aarch64 tests
and tested this patch.

Kernel: 4.18.0-305.el8.aarch64
CPU: 16x3.0GHz Ampere Alta / Arm Neoverse N1 cores

ZFS: 2.1.0-rc6
ZFS options: options spl spl_kmem_cache_slab_limit=65536 (see:
https://github.com/openzfs/zfs/issues/12150)

Postgres: 13.3 with and without the patch
Postgres config:

full_page_writes = on
wal_compression = on

Without patch:

starting vacuum...end.
transaction type: <builtin: TPC-B (sort of)>
scaling factor: 100
query mode: prepared
number of clients: 32
number of threads: 32
duration: 43200 s
number of transactions actually processed: 612557228
latency average = 2.257 ms
tps = 14179.551402 (including connections establishing)
tps = 14179.553286 (excluding connections establishing)

With patch:

starting vacuum...end.
transaction type: <builtin: TPC-B (sort of)>
scaling factor: 100
query mode: prepared
number of clients: 32
number of threads: 32
duration: 43200 s
number of transactions actually processed: 606967295
latency average = 2.278 ms
tps = 14050.164370 (including connections establishing)
tps = 14050.166007 (excluding connections establishing)

It does seem to help with on disk compression but it *might* have
caused more fragmentation.

Regards,
Omar

On Sat, May 29, 2021 at 10:22 PM Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr> wrote:
>
>
> Hello Yura,
>
> > didn't measure impact on raw performance yet.
>
> Must be done. There c/should be a guc to control this behavior if the
> performance impact is noticeable.
>
> --
> Fabien.
>
>