Database Reference
In-Depth Information
Database Replay allows the DBA to capture a workload on one database and replay it
on another. Database Replay is platform independent, so it is very useful when planning a
hardware or operating-system change to understand how workload performance might also
change. If you have multiple platforms or components available to test, you can conduct
a valid and repeatable performance comparison. The DBA and team can utilize Database
Replay to identify performance bottlenecks in the workload; determine if storage, CPU,
memory, or OS changes can remove the bottlenecks; and then run additional comparisons
after the changes are made.
These are the basic steps of Database Replay:
1. Capture the database workload.
2. Preprocess the workload.
3. Replay the workload.
4. Analyze the workload replay results.
Let's look at each of these individually.
Capturing a Workload
Make sure you have a replay database that is similar in data content to the capture system.
You can accomplish this by using Oracle or third-party tools to keep the data synchronized
close to the capture start time. Consider RMAN, a standby database, or export/import.
Oracle recommends a clean shutdown and restart of the capture database before begin-
ning workload capture. Start the database instance in restricted mode, start the capture,
and the instance will automatically switch to unrestricted. If a database instance restart is
not feasible, then quiesce the database or verify that there are no transactions running at
the time the workload capture begins.
Define either inclusion or exclusion workload filters to include or exclude specific user
sessions. The default is to capture all user sessions; you can use include or exclude filters
but not both.
Set up a capture at the operating system level, and make sure it's empty and has plenty of
space. The workload capture will stop if it runs out of space.
We start by capturing all the external client requests performed against a database and
writing the information to a platform-independent binary capture file. The workload capture
contains the following client request info:
SQL text
Bind variable values
Information about transactions
Workload capture can be initiated from Oracle Enterprise Manager or through the
DBMS_WORKLOAD_CAPTURE package. For this text, we will focus on EM.
At the Enterprise Manager database home page, click the Performance tab. From the
page shown in Figure 9.40, choose the Database Replay menu item.
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