RE: maxthr system statistic

Brandon,

I don't know much about this, but for what it's worth, the MAXTHR goes with the SLAVETHR and is used is the calculation of cost of parallel execution.

As it says, perhaps slightly misleadingly, in the 10053 trace file in 10gR2

    MAXTHR - maximum I/O system throughput     SLAVETHR - average slave I/O throughput

I think this means Oracle is monitoring the rate at which a query co-ordinator can acquire data from it's slaves checking for the maximum (hence the need that Christian saw to reset the value), and the rates at which the slaves are passing data to the QC and each other.

I believe that Oracle then uses these values in some way to adjust the cost of parallel queries by throwing in a fudge factor that chokes the degree used if it looks "optimistic" compared to

    maxthr /slavethr.

But I don't haven't worked out any details.

Regards

Jonathan Lewis
http://jonathanlewis.wordpress.com

Author: Cost Based Oracle: Fundamentals
http://www.jlcomp.demon.co.uk/cbo_book/ind_book.html

The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/faq/ind_faq.html

• Original Message -----
  >
  > Subject: RE: maxthr system statistic
  > Date: Fri, 19 Jan 2007 11:00:36 -0700
  > From: "Allen, Brandon" <Brandon.Allen_at_OneNeck.com>
  >
  > Thanks Christian & Mladen for sharing your thoughts, unfortunately they
  > only confirm my thoughts that nobody really knows how this statistic is
  > gathered or used - and based on the large variation in values on the
  > same system, maybe Oracle doesn't even know. I wonder if maybe it's not
  > used at all currently, but just there for use in a future version where
  > perhaps it will be better documented? I guess for now the safest
  > approach is that which you described Chris - gathering stats several
  > times and then taking the average (I'm guessing that's what you meant by
  > "good"?) value.
  >
  > Regards,
  > Brandon
  >
  

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