On Mon, May 17, 2010 at 3:52 AM, Piotr Legiecki <piotrlg@xxxxxxxxxx> wrote: > Scott Marlowe pisze: > >>>> So still I don't get this: select * from table; on old server takes 0,5 >>>> sec, >>>> on new one takes 6sec. Why there is so big difference? And it does not >>>> matter how good or bad select is to measure performance, because I don't >>>> measure the performance, I measure the relative difference. Somwhere >>>> there >>>> is a bottleneck. >>> >>> Yep, the network I'd say. How fast are things like scp between the >>> various machines? > > Sure it is, but not in a way one could expect: > - scp from 1000Gbit laptop to old server 27MB/sec > - scp from the same laptop to new server 70MB/sec > Both servers have 1000Gbit connection. So it is still mysterious why old > server makes 9x faster select? > I don't claim that something is slow on new (or even older) server. Not at > all. the application works fine (still on older machine). I only wonder > about those differences. Is one connecting via SSL? Is this a simple flat switched network, or are these machines on different segments connected via routers? >>>> 4. Machine. The new server has 5 SAS disks (+ 1 spare), but I don't >>>> remember >>>> how they are set up now (looks like mirror for system '/' and RAID5 for >>>> rest >>>> - including DB). size of the DB is 405MB >>> >>> Get off of RAID-5 if possible. A 3 Disk RAID-5 is the slowest >>> possible combination for RAID-5 and RAID-5 is generally the poorest >>> choice for a db server. > > Sure I know that RAID-5 is slower than mirror but anyway how much slower? > And for sure not as much as single ATA disk. Actually, given the amount of read read / write write RAID5 does, it can be slower than a single drive, by quite a bit. A mirror set only reads twice as fast, it writes the same speed as a single disk. RAID-5 is antithetical to good db performance (unless you hardly ever write). > >> I refer you to this classic post on the subject: >> http://www.mail-archive.com/pgsql-general@xxxxxxxxxxxxxx/msg93043.html > > Well, this thread is about benchmarking databases (or even worse, comparison > between two RDBMS). I'm not benchmarking anything, just compare one factor. That was a mis-post... -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
