On Sat, Apr 18, 2020 at 2:00 AM Ants Aasma <a...@cybertec.at> wrote: > On Thu, 16 Apr 2020 at 10:33, Pavel Stehule <pavel.steh...@gmail.com> wrote: > > what I know, pgbench cannot be used for testing spinlocks problems. > > > > Maybe you can see this issue when a) use higher number clients - hundreds, > > thousands. Decrease share memory, so there will be press on related spin > > lock. > > There really aren't many spinlocks left that could be tickled by a > normal workload. I looked for a way to trigger spinlock contention > when I prototyped a patch to replace spinlocks with futexes. The only > one that I could figure out a way to make contended was the lock > protecting parallel btree scan. A highly parallel index only scan on a > fully cached index should create at least some spinlock contention.
I suspect the snapshot-too-old "mutex_threshold" spinlock can become contended under workloads that generate a high rate of heap_page_prune_opt() calls with old_snapshot_threshold enabled. One way to do that is with a bunch of concurrent index scans that hit the heap in random order. Some notes about that: https://www.postgresql.org/message-id/flat/CA%2BhUKGKT8oTkp5jw_U4p0S-7UG9zsvtw_M47Y285bER6a2gD%2Bg%40mail.gmail.com
