Oracle AWR Report Load Profile
Oracle Tips by Burleson Consulting
AWR Report Summary
This section gives a glimpse of the database
workload activity that occurred within the snapshot interval. For
example, the load profile below shows that an average transaction
generates about 18K of redo data, and the database produces about
1.8K redo per second.
~~~~~~~~~~~~ Per Second Per Transaction
Redo size: 1,766.20 18,526.31
reads: 39.21 411.30
changes: 11.11 116.54
reads: 0.38 3.95
writes: 0.38 3.96
calls: 0.06 0.64
Parses: 2.04 21.37
parses: 0.14 1.45
Sorts: 1.02 10.72
Logons: 0.02 0.21
Executes: 4.19 43.91
The above statistics give an idea about the
workload the database experienced during the time observed. However,
they do not indicate what in the database is not working properly.
For example, if there are a high number of physical reads per
second, this does not mean that the SQLs are poorly tuned.
Perhaps this AWR report was built for a time
period when large DSS batch jobs ran on the database. This workload
information is intended to be used along with information from other
sections of the AWR report in order to learn the details about the
nature of the applications running on the system. The goal is to
get a correct picture of database performance.
The following list includes detailed
descriptions for particular statistics:
The amount of redo generated during this report.
Calculated as (Consistent Gets + DB Block Gets = Logical Reads).
The number of blocks modified during the sample interval.
The number of requests for a block that caused a physical I/O
Number of physical writes performed.
Number of user queries generated.
The total of all parses; both hard and soft.
The parses requiring a completely new parse of the SQL statement.
These consume both latches and shared pool area.
Soft parses are not listed but derived by subtracting the hard
parses from parses. A soft parse reuses a previous hard parse; hence
it consumes far fewer resources.
Parse activity statistics should be checked
carefully because they can immediately indicate a problem within the
application. For example, a database has been running several days
with a fixed set of applications, it should, within a course of
time, parse most SQLs issued by the applications, and these
statistics should be near zero.
If there are high values of Soft Parses or
especially Hard Parses statistics, such values should be taken as an indication that
the applications make little use of bind variables and produce large
numbers of unique SQLs. However, if the database serves
developmental purposes, high vales of these statistics are not bad.
The following information is also available in
the workload section:
% Blocks changed
per Read: 4.85 Recursive Call %: 89.89
transaction %: 8.56 Rows per Sort: 13.39
Blocks changed per Read statistic indicates that only 4.85
percent of all blocks are retrieved for update, and in this example,
the Recursive Call %
statistic is extremely high with about 90 percent. However, this
fact does not mean that nearly all SQL statements executed by the
database are caused by parsing activity, data dictionary management,
space management, and so on.
Remember, Oracle considers all SQL statements
executed within PL/SQL programs to be recursive. If there are
applications making use of a large number of stored PL/SQL programs,
this is good for performance. However, applications that do not
widely use PL/SQL may indicate the need to further investigate the
cause of this high recursive activity.
It is also useful to check the value of the
Rollback per transaction %
statistic. This statistic reports the percent of
transactions rolled back. In a production system, this value should
be low. If the output indicates a high percentage of transactions
rolled back, the database expends a considerable amount of work to
roll back changes made. This should be further investigated in
order to see why the applications roll back so often.
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