Database Reference
In-Depth Information
dep
2
1
0
t
Figure 27-1.
Recursive call depth and inter database call wait events
2
Calculating Response Time and Statistics
According to Millsap and Holt ([MiHo 2003]), the response time R represented by a SQL trace
file is defined as the sum of the elapsed time spent in database calls (
e
values) at recursive call
depth 0 (
dep=0
) plus the sum of all
ela
values from inter database call wait events. The wait time
(
ela
values) accumulated while processing a database call is rolled up into the parameter
e
of
the database call that engendered the wait. The categorization of wait events discussed in the
previous section is applied in the calculation of R. Time spent waiting for intra database call
wait events must not be added to R, since this would result in double counting. The
e
values of
a database call already contain the wait time of all intra database call wait events. Database
calls are emitted to trace files upon completion. This is why
WAIT
entries for intra database call
wait events appear 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 counted. To
promote a thorough understanding of how an extended SQL trace profiler calculates a resource
2.
The abbreviation msg is used instead of the word message in wait event names.
