| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Peter Geoghegan <pg(at)bowt(dot)ie> |
| Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, Julien Rouhaud <rjuju123(at)gmail(dot)com>, Simon Riggs <simon(dot)riggs(at)enterprisedb(dot)com>, Andrey Borodin <x4mmm(at)yandex-team(dot)ru>, Pengchengliu <pengchengliu(at)tju(dot)edu(dot)cn>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: suboverflowed subtransactions concurrency performance optimize |
| Date: | 2022-05-27 18:59:13 |
| Message-ID: | 20220527185913.64mkg7jkjkjajktx@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
On 2022-05-27 11:48:45 -0700, Peter Geoghegan wrote:
> On Fri, May 27, 2022 at 8:55 AM Andres Freund <andres(at)anarazel(dot)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.
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