Re: Improve WALRead() to suck data directly from WAL buffers when possible

Hi,

On 2023-01-14 00:48:52 -0800, Jeff Davis wrote:
> On Mon, 2022-12-26 at 14:20 +0530, Bharath Rupireddy wrote:
> > Please review the attached v2 patch further.
> 
> I'm still unclear on the performance goals of this patch. I see that it
> will reduce syscalls, which sounds good, but to what end?
> 
> Does it allow a greater number of walsenders? Lower replication
> latency? Less IO bandwidth? All of the above?

One benefit would be that it'd make it more realistic to use direct IO for WAL
- for which I have seen significant performance benefits. But when we
afterwards have to re-read it from disk to replicate, it's less clearly a win.

Greetings,

Andres Freund