> On Sat, Nov 10, 2018 at 8:37 PM Andres Freund <andres@anarazel.de> wrote: > > On 2018-11-10 20:18:33 +0100, Dmitry Dolgov wrote: > > > On Mon, 2 Jul 2018 at 15:54, Jesper Pedersen <jesper.pedersen@redhat.com> wrote: > > > > > > The patch from November 27, 2017 still applies (with hunks), > > > > > > https://commitfest.postgresql.org/18/1166/ > > > > > > passes "make check-world" and shows performance improvements. > > > > > > Keeping it in "Ready for Committer". > > > > Looks like for some reason this patch is failing to attract committers, any > > idea why? One of the plausible explanations for me is that the patch requires > > some more intensive benchmarking of different workloads and types of lock > > contention to make everyone more confident about it. > > Personally it's twofold: > > 1) It changes a lot of things, more than I think are strictly > necessary to achieve the goal. > > 2) While clearly the retry logic is not necessary anymore (it was > introduced when wait-queue was protected by a separate spinlock, which > could not atomically manipulated together with the lock's state), > there's reasons why it would be advantageous to keep: My original > patch for changing lwlocks to atomics, used lock xadd / fetch_add > to acquire shared locks (just incrementing the #shared bits after an > unlocked check) - obviously that can cause superfluous failures for > concurrent lock releases. Having the retry logic around can make > that safe. > > Using lock xadd to acquire shared locks turns out to be considerably > more efficient - most locks where the lock state is contended (rather > than just having processes wait), tend to have a very large fraction > of shared lockers. And being able to do such a lock acquisition on a > conteded cacheline with just a single locked operation, commonly > without retries, is quite beneficial.
Due to lack of response and taking into account this commentary, I'm marking this patch as "Returned with feedback", but hopefully I can pick it up later to improve.