On Fri, Oct 21, 2011 at 12:07 PM, Robert Haas <robertmh...@gmail.com> wrote: > On Fri, Oct 21, 2011 at 2:33 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: >>> I think HeapTupleSatisfiesMVCC is probably being skipped anyway in >>> this case, since all the heap pages should be PD_ALL_VISIBLE. >> >> Proves my point ;-) ... you're comparing a code path that's been beat on >> for *years* with one that just got written. > > I know. I wrote a chunk of it. :-) My point is just that it'd be > nice to make it better. > > Anyhow, here's the scoop. On my desktop machine running F14, running > SELECT sum(1) FROM pgbench_accounts in a tight loop, 60 s worth of > oprofile data: > > 176830 13.0801 postgres postgres > ExecProject
Hi Robert, count(*) and sum(1) do different things internally, and in my hands sum(1) is ~10% slower. I don't know how to dump the output of ExecBuildProjectionInfo into a human readable form, so I don't know the basis of the difference. But I wonder if using count(*) would lower the weight of the ExecProject function. Cheers, Jeff -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
