Re: suboverflowed subtransactions concurrency performance optimize

On 2022-05-27 11:48:45 -0700, Peter Geoghegan wrote:
> On Fri, May 27, 2022 at 8:55 AM Andres Freund <andres@anarazel.de> wrote:
> > > Anyway, how about if we clear this cache for subtrans whenever
> > > TransactionXmin is advanced and cachedFetchSubXid precedes it? The
> > > comments atop SubTransGetTopmostTransaction seem to state that we
> > > don't care about the exact topmost parent when the intermediate one
> > > precedes TransactionXmin. I think it should preserve the optimization
> > > because anyway for such cases there is a fast path in
> > > SubTransGetTopmostTransaction.
> >
> > There's not even a proof this does speed up anything useful! There's not a
> > single benchmark for the patch.
> 
> I find it hard to believe that there wasn't even a cursory effort at
> performance validation before this was committed, but that's what it
> looks like.

Yea. Imo this pretty clearly should be reverted. It has correctness issues,
testing issues and we don't know whether it does anything useful.