"db file sequential read" call durations reported by Oracle are not service times (S); they are response times (R), which include both service time and queueing delay (S + W). They are not suitable inputs into the S slot in an M/M/m queueing model. Cary Millsap Method R Corporation http://method-r.com On Mon, Sep 26, 2011 at 10:17 PM, Sidney Chen <huanshengchen@xxxxxxxxx>wrote: > Hi, > When reading the Topic of M/M/m Module in the book <<Optimizing Oracle > Performance>> by Gary Millsap, I have the idea to verify if our I/O > subsystem can fit the M/M/m module. > > The db is IO intense, 80% db time is spent on "db file sequential read", > and the avg wait time is 15ms. > 1. to do the assessment, I extract 3357 lines in one 10046 trace file > 2. compute the ela time as second(divide by 1000000, keep the distribution > compact) > 3. using the mdist.pl to tell if the elapse time for "db file sequential > read" fit the "exponential distribution". > > the result is reject, so i wonder if there are accurate methods to assess. > Any advise is appreciated. > > oracle: ~/scripts$ perl mdist.pl 2.lst > Hypothesis: Data are exponentially distributed with mean > 0.0155063946976467 > Test result: n=2 V=1143.25 p=1.000 > Verdict: *Reject* > > > > > --original record in 10046 trace file > WAIT #19: nam='db file sequential read' ela= 26431 file#=207 block#=258517 > blocks=1 obj#=206447 tim=1284706983664908 > WAIT #19: nam='db file sequential read' ela= 11191 file#=108 block#=1351954 > blocks=1 obj#=206444 tim=1284706983677002 > WAIT #19: nam='db file sequential read' ela= 11836 file#=25 block#=294842 > blocks=1 obj#=206444 tim=1284706983689523 > WAIT #19: nam='db file sequential read' ela= 6268 file#=25 block#=472857 > blocks=1 obj#=206444 tim=1284706983696181 > WAIT #19: nam='db file sequential read' ela= 6339 file#=108 block#=1348802 > blocks=1 obj#=206444 tim=1284706983702664 > WAIT #19: nam='db file sequential read' ela= 7363 file#=25 block#=434781 > blocks=1 obj#=206444 tim=1284706983710368 > WAIT #19: nam='db file sequential read' ela= 12006 file#=176 block#=489651 > blocks=1 obj#=206444 tim=1284706983722477 > WAIT #19: nam='db file sequential read' ela= 18163 file#=107 block#=1728592 > blocks=1 obj#=206444 tim=1284706983740767 > WAIT #19: nam='db file sequential read' ela= 24003 file#=107 block#=1740869 > blocks=1 obj#=206444 tim=1284706983765194 > WAIT #19: nam='db file sequential read' ela= 4780 file#=25 block#=473096 > blocks=1 obj#=206444 tim=1284706983770782 > WAIT #19: nam='db file sequential read' ela= 6644 file#=25 block#=431224 > blocks=1 obj#=206444 tim=1284706983777508 > WAIT #19: nam='db file sequential read' ela= 20201 file#=107 block#=1747395 > blocks=1 obj#=206444 tim=1284706983797791 > WAIT #5: nam='db file sequential read' ela= 89939 file#=207 block#=359305 > blocks=1 obj#=206447 tim=1284706984136333 > WAIT #5: nam='db file sequential read' ela= 21708 file#=25 block#=292852 > blocks=1 obj#=206444 tim=1284706984158777 > > --record in 2.lst, ela divided by 1000000 > .026431 > .011191 > .011836 > .006268 > .006339 > .007363 > .012006 > .018163 > .024003 > .00478 > .006644 > .020201 > .089939 > .021708 > > -- > Sidney Chen > Blog: *http://sid.gd* <http://sid.gd> > > > -- > //www.freelists.org/webpage/oracle-l > > > -- //www.freelists.org/webpage/oracle-l