Re: Reducing contention for the LockMgrLock

Alvaro Herrera <alvherre@commandprompt.com> writes:
> Is hashtable overhead all that large?  Each table could be made
> initially size-of-current-table/N entries.  One problem is that
> currently the memory freed from a hashtable is not put back into shmem
> freespace, is it?

Yeah; the problem is mainly that we'd have to allocate extra space to
allow for unevenness of usage across the multiple hashtables.  It's hard
to judge how large the effect would be without testing, but I think that
this problem would inhibit us from having dozens or hundreds of separate
partitions.

A possible response is to try to improve dynahash.c to make its memory
management more flexible, but I'd prefer not to get into that unless
it becomes really necessary.  A shared freespace pool would create a
contention bottleneck of its own...
        regards, tom lane