On 2016-07-13 16:39:58 -0400, Tom Lane wrote: > Robert Haas <robertmh...@gmail.com> writes: > > On Wed, Jul 13, 2016 at 1:10 PM, Tomas Vondra > > <tomas.von...@2ndquadrant.com> wrote: > > What's not clear to me is to what extent slowing down pfree is an > > acceptable price for improving the behavior in other ways. I wonder > > how many of the pfree calls in our current codebase are useless or > > even counterproductive, or could be made so. > > I think there's a lot, but I'm afraid most of them are in contexts > (pun intended) where aset.c already works pretty well, ie it's a > short-lived context anyway.
FWIW, hacking up the aset/mcxt.c to use a trivial allocator with less overhead (i.e. just hand out sections out of a continuous block of memory) results in a noticeable speedup in parse heavy workloads. It's a bit ugly though, because of the amount of retail pfrees in random places. > The areas where we're having pain are > where there are fairly long-lived contexts with lots of pfree traffic; > certainly that seems to be the case in reorderbuffer.c. Because they're > long-lived, you can't just write off the pfrees as ignorable. That's a problem too. > I wonder whether we could compromise by reducing the minimum "standard > chunk header" to be just a pointer to owning context, with the other > fields becoming specific to particular mcxt implementations. That would > be enough to allow contexts to decide that pfree was a no-op, say, or that > they wouldn't support GetMemoryChunkSpace(), without having to decree that > misuse can lead to crashes. But that's still more than zero overhead > per-chunk. I think that's a sensible compromise for some use-cases (e.g. parsing, parse analysis, potentially expression contexts). Andres -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
