I do believe that I have async I/O on VxFS (no I don't have ODM). From an earlier blog post [0]: oracle:~/sr $ strace -c -p 12605 Process 12605 attached - interrupt to quit Process 12605 detached % time seconds usecs/call calls errors syscall —— ———– ———– ——— ——— —————- 80.66 1.142811 298 3831 io_getevents 7.26 0.102820 51 2004 io_submit Don. [0] http://seilerwerks.wordpress.com/2007/12/19/a-sub-prime-io-primer/ On Fri, Feb 22, 2008 at 3:16 PM, Finn Jorgensen <finn.oracledba@xxxxxxxxx> wrote: > As I understand it vxfs does not support async IO. When you say "asynch > reads on the new system", I'm thinking you mean direct reads? > > When not using directio on vxfs and you look at your truss output are there > a lot of "fdsync" calls, which takes a long time (like 0.01 seconds per > call)? If so, that's your culprit. Going to directio can eliminate these, > but there's a level of patching on both Solaris 10 and veritas together with > a kernel setting that pretty much eliminates the need for that setup as the > fdsync calls are made so fast they can be ignored. Have you SA's check into > paching solaris 10 and veritas to eliminate the slow fdsync calls. > > Finn > > > > > On 2/22/08, Josh Collier <Josh.Collier@xxxxxxxxxxxx> wrote: > > > > > > the old system is on ufs, the new is vxfs. > > > > I've narrowed it down to the difference in synchronous disk reads. the > async reads on the new system are much faster. the synchronous disk reads > are slower. > > > > > > > > ________________________________ > From: Finn Jorgensen [mailto:finn.oracledba@xxxxxxxxx] > > Sent: Friday, February 22, 2008 7:01 AM > > To: Josh Collier > > Cc: oracle-l@xxxxxxxxxxxxx > > Subject: Re: Db file scattered reads vs. direct path reads > > > > > > > > What type of filesystem are you on? What differences are there between the > old system and the new apart from the storage array? > > > > Finn > > > > > > On 2/20/08, Josh Collier <Josh.Collier@xxxxxxxxxxxx> wrote: > > > > > > > > > Hi, > > > > > > I've got a conundrum. We've got a new disk system. When I full scan a > table with the nocache hint the trace files record lots of reads like this > > > > > > WAIT #1: nam='db file scattered read' ela= 38471 file#=777 block#=238789 > blocks=64 obj#=2805234 tim=359927798919 > > > > > > And the query takes 11 minutes for a 19gb table, much slower than our > old system > > > > > > When I enforce direct path reads with the following parameter > > > :alter session set "_serial_direct_read" = true > > > > > > The trace files record lots of reads like this > > > > > > WAIT #1: nam='direct path read' ela= 5 file number=777 first dba=238789 > block cnt=64 obj#=2805234 tim=343398354853 > > > > > > And the query returns in 3 minutes > > > > > > What would cause the scattered reads to be so much slower than the > direct path reads? > > > > > > I've enabled direct io on the db and verified it via truss. > > > > > > Version is 10.2.0.1 > > > Solaris 10 > > > > > > > > > > > > > > > > > > > > > -- Don Seiler http://seilerwerks.wordpress.com ultimate: http://www.mufc.us -- //www.freelists.org/webpage/oracle-l