Using the Exadata Simulation Workflow

The Exadata simulation workflow enables you to simulate the effects of an Exadata Storage Server installation on the performance of a SQL workload.

Oracle Exadata provides extremely large I/O bandwidth coupled with a capability to offload SQL processing from the database to storage. This allows Oracle Database to significantly reduce the volume of data sent through the I/O interconnect, while at the same time offloading CPU resources to the Exadata storage cells.

SQL Performance Analyzer can analyze the effectiveness of Exadata SQL offload processing by simulating an Exadata Storage Server installation and measuring the reduction in I/O interconnect usage for the SQL workload.

Running the Exadata simulation does not require any hardware or configuration changes to your system. After you select a SQL tuning set, SQL Performance Analyzer creates a task and performs an initial trial with the Exadata Storage Server simulation disabled. SQL Performance Analyzer then performs a second trial with the Exadata Storage Server simulation enabled. SQL Performance Analyzer then compares the two trials using the I/O Interconnect Bytes comparison metric and generates a SQL Performance Analyzer report, which estimates the amount of data that would not need to be sent from the Exadata storage cells to the database if Oracle Exadata is being used. In both SQL trials, the SQL statements are executed to completion and I/O interconnect bytes measurements are taken as the actual and simulated Exadata values for the first and second trials, respectively. The measured change in I/O interconnect bytes provides a good estimate of how much filtering can be performed in the Exadata storage cells and, in turn, the amount of CPU that normally would be used to process this data, but now can be offloaded from the database.

Note:

Using the Exadata simulation will not result in any plan changes. Execution plans do not change in an Exadata Storage Server installation because the simulation focuses on measuring the improvement in I/O interconnect usage. Moreover, I/O interconnect bytes will not increase, except when data compression is used (see next note), because Oracle Exadata will only decrease the amount of data sent to the database.

Note:

Because I/O interconnect bytes is the only metric used to measure the performance change impact of using an Exadata Storage Server installation, it will not work properly if Oracle Exadata is used with data compression. Since Exadata storage cells also decompress data, the I/O interconnect bytes with Oracle Exadata (or the second SQL trial) of a SQL statement may be greater than the I/O interconnect bytes without Oracle Exadata (or the first SQL trial) where the data is compressed. This comparison will be misleading because the SQL statement will be reported as a regression; when in fact, it is not.

Note:

The Exadata simulation workflow is used to simulate an Exadata Storage Server installation on non-Exadata hardware. To test changes on Exadata hardware, use the standard SQL Performance Analyzer workflows.

Note:

The Exadata simulation is supported for DSS and data warehouse workloads only.

To use the SQL Performance Analyzer Exadata simulation workflow:

  1. On the SQL Performance Analyzer page, under SQL Performance Analyzer Workflows, click Exadata Simulation.

    The Exadata Simulation page appears.

    Description of the illustration spa_exadata_sim.gif follows
    Description of the illustration spa_exadata_sim.gif

  2. In the Task Name field, enter the name of the task.

  3. In the SQL Tuning Set field, enter the name of the SQL tuning set that contains the SQL workload to be analyzed.

    Alternatively, click the search icon to search for a SQL tuning set using the Search and Select: SQL Tuning Set window.

    The selected SQL tuning set now appears in the SQL Tuning Set field.

  4. In the Description field, optionally enter a description of the task.

  5. In the Per-SQL Time Limit list, determine the time limit for SQL execution during the trial by performing one of the following actions:

    • Select 5 minutes.

      The execution will run each SQL statement in the SQL tuning set up to 5 minutes and gather performance data.

    • Select Unlimited.

      The execution will run each SQL statement in the SQL tuning set to completion and gather performance data. Collecting execution statistics provides greater accuracy in the performance analysis but takes a longer time. Using this setting is not recommended because the task may be stalled by one SQL statement for a prolonged time period.

    • Select Customize and enter the specified number of seconds, minutes, or hours.

  6. In the Schedule section:

    1. In the Time Zone list, select your time zone code.

    2. Select Immediately to start the task now, or Later to schedule the task to start at a time specified using the Date and Time fields.

  7. Click Submit.

    The SQL Performance Analyzer page appears.

    In the SQL Performance Analyzer Tasks section, the status of this task is displayed. To refresh the status icon, click Refresh. After the task completes, the Status field changes to Completed.

    Description of the illustration spa_tasks_exadata.gif follows
    Description of the illustration spa_tasks_exadata.gif

  8. In the SQL Performance Analyzer Tasks section, select the task and click the link in the Name column.

    The SQL Performance Analyzer Task page appears.

    Description of the illustration spa_task_exadata_sim.gif follows
    Description of the illustration spa_task_exadata_sim.gif

    This page contains the following sections:

    • SQL Tuning Set

      This section summarizes information about the SQL tuning set, including its name, owner, description, and the number of SQL statements it contains.

    • SQL Trials

      This section includes a table that lists the SQL trials used in the SQL Performance Analyzer task.

    • SQL Trial Comparisons

      This section contains a table that lists the results of the SQL trial comparisons

  9. Click the icon in the Comparison Report column.

    The SQL Performance Analyzer Task Result page appears.

  10. Review the results of the performance analysis, as described in "Reviewing the SQL Performance Analyzer Report Using Oracle Enterprise Manager".

    Any SQL performance improvement with the Exadata simulation between the first and second trials is captured in the report. In general, you can expect a greater impact if the SQL workload contains queries that scan a large number of rows or a small subset of table columns. Conversely, a SQL workload that queries indexed tables or tables with fewer rows will result in a lesser impact from the Exadata simulation.