*From*: "Christian Antognini" <Christian.Antognini@xxxxxxxxxxxx>*To*: <Brandon.Allen@xxxxxxxxxxx>*Date*: Fri, 19 Jan 2007 09:23:02 +0100

Brandon > Does anybody have a good understanding of how the maxthr > metric is computed or how it's used by the CBO? A couple of years ago I spent some time investigating how system stats are computed. It was not a problem to find out how MBRC, SREADTIM and MREADTIM are computed. In fact they are simply based on values available in x$kcfio and v$sysstat. For CPUSPEED, MAXTHR and SLAVETHR it's a different story. The problem is that callouts to a C library (DBMS_STATS_LIB) are performed to get them. For example for the throughput it seams they have two functions: oracle@trantor:~/ [A1020] nm $ORACLE_HOME/lib/libserver10.a | grep kdap.*thr 00012004 t kdapgetthr 00012034 t kdapresetthr I stopped my research at this point. So, no idea what they really do... My guess is the following: - when the gathering of system stats is started the function kdapresetthr is called to reset the variable(s) storing the throughput information - the system, while doing I/Os, stores in the variable(s) the maximum throughput - when the gathering of system stats is stopped the function kdapgetthr is called to get the throughput information > I'm just curious because I've gathered system stats 5 times > in the past few days and keep getting wildly different values > for this metric while the rest are relatively constant: That match what I observed on systems where system stats are gathered. For this reason I presently advice my customers to gather system stats not in one simple call, but to gather them in a user-defined table at regular intervals (e.g. 1h) for a week or so. Then plot a nice chart with Excel and find out what "good" values are. HTH Chris -- http://www.freelists.org/webpage/oracle-l

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