On Tue, Oct 7, 2014 at 6:06 AM, Robert Haas <robertmh...@gmail.com> wrote: > I'm not up on the details of what Peter's patch does with heavyweight > locking, but I'd say it this way: if the patch uses heavyweight > locking routinely, that's probably not going to scale well. If > the patch detects possible conflicts and uses heavyweight locking only > in those cases and for the specific purpose of untangling those > conflicts, then that might well be OK.
The patch opportunistically tries to use shared buffer locks when a conflict is expected, when we restart (but only on the unique index where a conflict was detected). So in the event of a lot of near-conflicts, the hwlock traffic is quite modest. That, combined with the fact that it uses what I've called "an index scan with an identity crisis" (could be a near-insertion + hwlock in advance of insertion proper, or just something akin to a regular index scan) makes it perform best (at least with one or two unique indexes, which is what I tested a few months back). It does not have a pre-check that is always wasted with insertion-heavy workloads. Now, we're not talking about a huge advantage here (I should re-test that). And, in case I wasn't clear: I have misgivings about all 3 designs. Like Simon, I think it is appropriate that we figure out our exact requirements using the two working prototype patches. Although, right now #1 and #2 (the prototypes) seem quite comparable, that might just be down to a failure of imagination. It's hard to be completely confident about something like that. -- Peter Geoghegan -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers