Calculating Response Time and Statistics for Oracle Performance Tuning
According to so many books, the response time R correspond
to a SQL trace file is identified as the sum of the elapsed time exhausted in
database calls (e values) at recursive call depth 0 (dep=0) plus the sum of all
elapsed values from inter and recursive database call wait events. The wait
time (elapsed values) collected while routing a database call is rolled up into
the parameter e of the database call that stimulated the wait. The classification
of wait events is pertained in the calculation of R. Time used up waiting for
intra database call wait events (all calls including recursive) must not be added
to R, since this would outcome in double calculating. The e values of a
database call already include the wait time of all intra database call wait
events. Database calls are produced to trace files upon conclusion. This is why
WAIT entries for intra database call wait events become visible before the
PARSE, EXEC, and FETCH entries that engendered them. Runtime statistics, such
as consistent reads, physical writes, and db block gets at recursive call
depths other than zero are rolled up into PARSE, EXEC, and FETCH calls at
recursive call depth 0. Just like ela values of intra database call wait
events, these must not be double calculated. To promote a thorough
understanding of how an extended SQL trace profiler calculates a resource, we
should need to understand properly its mechanism. Then and only we are able to
calculate total response time matrix as well as root cause of SQL statement for
performing poor.
Database call statistics at recursive call (internal calls implicit
cursors) deepness other than zero are revolved up into the statistics at
recursive call depth 0. To determine the total number of db block gets in the
trace file, we must think only cu parameter values of PARSE, EXEC, and FETCH
entries with dep=0. The database call parameter cu (for current read) keep in touches
to the statistic db block gets. The fact that the total number of db block gets
as determined by querying V$SESSTAT was nine confirms that database call statistics
at lower levels are rolled up into statistics at recursive call depth 0. This is methodology of calculation of response time from v$sesstat and if you get trace file then you can get whole idea about response time matrix of problematic SQL.
