On Oct 12, 2010, at 11:58 AM, Tom Lane wrote: > Jesper Krogh <jes...@krogh.cc> writes: >> On 2010-10-12 19:07, Tom Lane wrote: >>> Anyway, if anyone is hot to make COUNT(*) faster, that's where to look. > >> Just having 32 bytes bytes of "payload" would more or less double >> you time to count if I read you test results correctly?. .. and in the >> situation where diskaccess would be needed .. way more. > >> Dividing by pg_relation_size by the amout of tuples in our production >> system I end up having no avg tuple size less than 100bytes. > > Well, yeah. I deliberately tested with a very narrow table so as to > stress the per-row CPU costs as much as possible. With any wider table > you're just going to be I/O bound.
On a wimpy disk, I/O bound for sure. But my disks go 1000MB/sec. No query can go fast enough for them. The best I've gotten is 800MB/sec, on a wide row (average 800 bytes). Most tables go 300MB/sec or so. And with 72GB of RAM, many scans are in-memory anyway. A single SSD with supercapacitor will go about 500MB/sec by itself next spring. I will easily be able to build a system with 2GB/sec I/O for under $10k. -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
