On Tue, Aug 2, 2022 at 4:46 PM David Rowley <dgrowle...@gmail.com> wrote:
> On Wed, 20 Jun 2018 at 19:08, David Rowley <david.row...@2ndquadrant.com> > wrote: > > I'll submit it again when there more consensus that we want this. > > Waking up this old thread again. If you don't have a copy, the entire > thread is in [1]. > > The remaining item that seemed to cause this patch to be rejected was > raised in [2]. The summary of that was that it might not be a good > idea to allow parallel aggregation of string_agg() and array_agg() as > there might be some people who rely on the current ordering they get > without having an ORDER BY clause in the aggregate function call. Tom > mentioned in [3] that users might not want to add an ORDER BY to their > aggregate function because the performance of it is terrible. That > was true up until 1349d2790 [4], where I changed how ORDER BY / > DISTINCT aggregation worked to allow the planner to provide pre-sorted > input rather than always having nodeAgg.c do the sorting. I think > this removes quite a lot of the argument against the patch, but not > all of it. So here goes testing the water on seeing if any opinions > have changed over the past few years? > > A rebased patch is attached. > > David > > [1] > https://www.postgresql.org/message-id/flat/CAKJS1f98yPkRMsE0JnDh72%3DAQEUuE3atiCJtPVCtjhFwzCRJHQ%40mail.gmail.com#8bbce15b9279d2da2da99071f732a99d > [2] https://www.postgresql.org/message-id/6538.1522096...@sss.pgh.pa.us > [3] https://www.postgresql.org/message-id/18594.1522099...@sss.pgh.pa.us > [4] > https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=1349d2790bf48a4de072931c722f39337e72055e Hi, For array_agg_combine(): + if (state1->alen < reqsize) + { + /* Use a power of 2 size rather than allocating just reqsize */ + state1->alen = pg_nextpower2_32(reqsize); ... + state1->nelems = reqsize; I wonder why pg_nextpower2_32(reqsize) is used in the if block. It seems reqsize should suffice. Cheers
