Re: GUC-ify walsender MAX_SEND_SIZE constant

Hi Andres,

On Fri, 9 Feb 2024 at 22:33, Andres Freund <andres(at)anarazel(dot)de> wrote:

> On 2024-01-19 23:04:50 +0330, Majid Garoosi wrote:
> > Following is the description which is also written in the commit message:
> > MAX_SEND_SIZE parameter was used in WALSender to limit maximum size of
> > a WAL data packet sent to a WALReceiver during replication. Although
> > its default value (128kB) was a reasonable value, it was written in
> > 2010. Since the hardwares have changed a lot since then, a PostgreSQL
> > user might need to customize this value.
> > For example, if a database's disk has a high bandwidth and a high
> > latency at the same time, it makes more sense to read bigger chunks of
> > data from disk in each iteration. One example of such disks is a remote
> > disk. (e.g. an RBD volume)
>
> The way we read the WAL data is perfectly prefetchable by the the OS, so I
> wouldn't really expect gains here. Have you actually been able to see a
> performance benefit by increasing MAX_SEND_SIZE?
>

Yes, I have seen a huge performance jump. Take a look at here
<https://www.postgresql.org/message-id/CAFWczPvi_5FWH%2BJTqkWbi%2Bw83hy%3DMYg%3D2hKK0%3DJZBe9%3DhTpE4w%40mail.gmail.com>
for
more info.

Best
Majid