Thread

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

SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com> — 2023-01-25T20:27:30Z

On Sat, Jan 14, 2023 at 12:34 PM Andres Freund <andres@anarazel.de> wrote:

> 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.
>

 +1. Archive modules rely on reading the wal files for PITR. Direct IO for
WAL requires reading these files from disk anyways for archival. However,
Archiving using utilities like pg_receivewal can take advantage of this
patch together with direct IO for WAL.

Thanks,
Satya