Re: Parallel Query Performance

"Andy Marden" <amarden_at_altavista.net> wrote in message news:<k3g87.3954$Bp3.80305_at_news2-hme0>...
> Got a funny one here. We're running 8.1.7 on AIX 4.1.3 (RS6000s, 64 bit), 4
> procs, 4Gb memory, LVM software striped RAID 0 disks (128Kb stripe width)
> over 12 disks. All this is for a Data Warehouse. Running some insert
> statements with queries shows large performance improvement for parallel 4
> over single-threaded, not surprisingly, although we seem to see more than a
> 4x performance, which is a little wierd. What's strange, is that running 2
> of these together dramatically worsens overall performance - actually making
> it worse than running them serially single-threaded. I would expect to see a
> slight degradation running them together, perhaps, if we were CPU or I/O
> bound, but I don't believe we should be. I/O wait is minimal.
>
> Has anyone seen anything like this before?
>
> Cheers
>
> Andy

Assuming you're running with TIMED_STATISTICS turned on - look at the output from v$system_event before and after the run and you should see where all the waited tim in the database was spent (assuming it is a database problem)
Or get hold of statspack and gather stats for the two different run and look at the output described above.
Not clear from your message if your're running multiple inserts on the same objects concurrently - multiple queries should'nt matter from a DB perspective unless you're ruuning it issues allocating sort space etc etc. Received on Fri Jul 27 2001 - 17:10:38 CDT