Re: strange perf regression with data checksums

Hi,

On 2025-05-19 15:45:01 -0400, Peter Geoghegan wrote:
> On Mon, May 19, 2025 at 3:37 PM Andres Freund <andres@anarazel.de> wrote:
> > I think we can do better - something like
> >
> > #ifdef PG_HAVE_8BYTE_SINGLE_COPY_ATOMICITY
> >     lsn = PageGetLSN(page);
> > #else
> >     buf_state = LockBufHdr(bufHdr);
> >     lsn = PageGetLSN(page);
> >     UnlockBufHdr(bufHdr, buf_state);
> > #endif
> >
> > All perf relevant systems support reading 8 bytes without a chance of
> > tearing...
> 
> Even assuming that this scheme works perfectly, I'd still like to
> pursue the idea I had about fixing this in nbtree.
> 
> The relevant nbtree code seems more elegant if we avoid calling
> BufferGetLSNAtomic() unless and until its return value might actually
> be useful. It's quite a lot easier to understand the true purpose of
> so->currPos.lsn with this new structure.

I'm not against that - ISTM we should do both.

Greetings,

Andres Freund