Database Reference
In-Depth Information
This information is especially useful to find out whether there are other applications consuming CPU on the
database server. For that purpose, you need to compare the CPU utilization reported by time model statistics with
the
BUSY_TIME
statistic. If they're close to each other, you know that most of the CPU is consumed by the database
instance you're connected to.
Time Model Statistics
You can know what kind of processing a database engine is doing on behalf of an application by looking at the
time
model
statistics. The purpose of time model statistics is to show the amount of time spent performing key operations
like opening new sessions, parsing SQL statements, and processing calls with one of the engines (SQL, PL/SQL, Java
and OLAP) provided by Oracle Database. In addition, some figures about background processing are also given.
Time model statistics are based on a small number of figures organized in two independent trees: one for the
background processing carried out by the database instance itself, and another for the foreground processing (the
processing performed on behalf of an application). Figures
4-2
and
4-3
show not only the statistics associated with
background processing and foreground processing, but also the relationship between them. For example, according
to Figure
4-3
,
parse time elapsed
is a child of
DB time
and the parent of
hard parse elapsed time
. The name of
each statistic is basically self-explanatory. For a detailed description, refer to the “V$SESS_TIME_MODEL” section of
the
Oracle Database Reference
manual.
Figure 4-2.
The tree formed by time model statistics for background processing
Figure 4-3.
The tree formed by time model statistics for foreground processing
Because time model statistics are separated into two trees, the total amount of processing can be calculated by
summing up
DB time
and
background elapsed time
. Note that both statistics include CPU usage as well as the sum
of all wait events except for the ones that belongs to the Idle wait class (the next section provides more information
about wait classes).
The time reported by a child in the tree is contained within its parent in the tree. But be careful—this doesn't mean
that adding up the time reported by all children gives the time reported by their parent. In fact, not only is the time of a
