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

On Fri, Oct 20, 2023 at 10:19 PM Bharath Rupireddy
<bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:
>
> On Thu, Oct 12, 2023 at 4:13 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
> >
> > On 2023-10-03 16:05:32 -0700, Jeff Davis wrote:
> > > On Sat, 2023-01-14 at 12:34 -0800, Andres Freund wrote:
> > > > 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.
> > >
> > > Does this patch still look like a good fit for your (or someone else's)
> > > plans for direct IO here? If so, would committing this soon make it
> > > easier to make progress on that, or should we wait until it's actually
> > > needed?
> >
> > I think it'd be quite useful to have. Even with the code as of 16, I see
> > better performance in some workloads with debug_io_direct=wal,
> > wal_sync_method=open_datasync compared to any other configuration. Except of
> > course that it makes walsenders more problematic, as they suddenly require
> > read IO. Thus having support for walsenders to send directly from wal buffers
> > would be beneficial, even without further AIO infrastructure.
>
> I'm attaching the v11 patch set with the following changes:
> - Improved input validation in the function that reads WAL from WAL
> buffers in 0001 patch.
> - Improved test module's code in 0002 patch.
> - Modernized meson build file in 0002 patch.
> - Added commit messages for both the patches.
> - Ran pgindent on both the patches.
>
> Any thoughts are welcome.

I'm attaching v12 patch set with just pgperltidy ran on the new TAP
test added in 0002. No other changes from that of v11 patch set.

--
Bharath Rupireddy
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com