Re: Patch: fix lock contention for HASHHDR.mutex

> It'd really like to see it being replaced by a queuing lock
> (i.e. lwlock) before we go there. And then maybe partition the
> freelist, and make nentries an atomic.

I believe I just implemented something like this (see attachment). The
idea is to partition PROCLOCK hash table manually into NUM_LOCK_
PARTITIONS smaller and non-partitioned hash tables. Since these tables
are non-partitioned spinlock is not used and there is no lock
contention.

On 60-core server we gain 3.5-4 more TPS according to benchmark
described above. As I understand there is no performance degradation in
other cases (different CPU, traditional pgbench, etc).

If this patch seems to be OK I believe we could consider applying the
same change not only to PROCLOCK hash table.