Re: Buffer locking is special (hints, checksums, AIO writes) - Mailing list pgsql-hackers

On Tue, Nov 25, 2025 at 3:46 PM Andres Freund <andres@anarazel.de> wrote:
>
>
> > > > I presume you didn't do this because HeapTupleSatisifiesMVCC() for
> > > > SNAPSHOT_MVCC calls the non-batch version (and, of course,
> > > > HeapTupleSatisifiesVisibility() is the much more common case).
> > > >
> > > > if (TransactionIdIsValid(xid))
> > > > {
> > > >         if (BufferIsPermanent(buffer))
> > > >         {
> > > >                 /* NB: xid must be known committed here! */
> > > >                 XLogRecPtr    commitLSN = TransactionIdGetCommitLSN(xid);
> > > >
> > > >                 if (XLogNeedsFlush(commitLSN) &&
> > > >                         BufferGetLSNAtomic(buffer) < commitLSN)
> > > >                 {
> > > >                         /* not flushed and no LSN interlock, so don't
> > > > set hint */
> > > >                         return; false;
> > > >                 }
> > > >         }
> > > > }
> > > >
> > > > Separately, I was thinking, should we assert here about having the
> > > > right lock type?
> > >
> > > Not sure I get what assert of what locktype where?
> >
> > In SetHintBitsExt() that we have share-exclusive or above.
>
> We *don't* necessarily hold that though, it'll just be acquired by
> BufferBeginSetHintBits().  Or do you mean in the SHB_ENABLED case?

Yea, in the enabled case. Also, can't we skip the whole

    if (TransactionIdIsValid(xid))
    {
        if (BufferIsPermanent(buffer))
        {
            /* NB: xid must be known committed here! */
            XLogRecPtr    commitLSN = TransactionIdGetCommitLSN(xid);

            if (XLogNeedsFlush(commitLSN) &&
                BufferGetLSNAtomic(buffer) < commitLSN)
            {
                /* not flushed and no LSN interlock, so don't set hint */
                return;
            }
        }
    }

part if state is SHB_DISABLED?

- Melanie