On Mon, Dec 11, 2017 at 4:10 PM, Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> Thank you for updating the patch. Here is two minor comments.
>
> + * we acquire the same relation extension lock repeatedly. nLocks is 0 is the
> + * number of times we've acquired that lock;
>
> Should it be "nLocks is the number of times we've acquired that lock:"?
Yes.
> + /* Remember lock held by this backend */
> + held_relextlock.relid = relid;
> + held_relextlock.lock = relextlock;
> + held_relextlock.nLocks = 1;
>
> We set held_relextlock.relid and held_relextlock.lock again. Can we remove them?
Yes.
Can you also try the experiment Andres mentions: "Measure two COPYs to
relations on different filesystems, reduce N_RELEXTLOCK_ENTS to 1, and
measure performance. Then increase the concurrency of the copies to
each relation." We want to see whether and how much this regresses
performance in that case. It simulates the case of a hash collision.
--
Robert Haas
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