What does ALTER SESSION do in Oracle?
ALTER SESSION is a powerful command in Oracle database management that allows users to modify the session settings for their current session. This command is particularly useful when you need to change certain attributes of the session that affect the way queries are executed or how the database behaves. In this article, we will explore the various aspects of ALTER SESSION and its impact on Oracle database sessions.
The primary purpose of ALTER SESSION is to alter the session parameters for the current user. These parameters can include database-related settings, such as the default tablespace, or session-related settings, such as the sort area size. By modifying these parameters, users can optimize their database sessions for better performance and efficiency.
One of the most common uses of ALTER SESSION is to change the default tablespace for a session. This can be particularly useful when working with temporary tables or when you want to ensure that all objects created during the session are stored in a specific tablespace. To change the default tablespace, you can use the following command:
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ALTER SESSION SET DEFAULT_TABLESPACE = your_tablespace_name;
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Another important aspect of ALTER SESSION is the ability to modify session-related settings. For example, you can adjust the sort area size to accommodate larger sorting operations or change the number of rows fetched per query to improve performance. Here are some examples of session-related settings that can be altered:
– Sort area size:
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ALTER SESSION SET sort_area_size = 10M;
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– Number of rows fetched per query:
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ALTER SESSION SET rows_per_batch = 1000;
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ALTER SESSION also allows you to enable or disable certain features within the database. For instance, you can turn on or off the optimizer hints to control the execution plan of a query. This can be helpful when you want to force the database to use a specific plan or when you are troubleshooting performance issues. Here’s an example of enabling an optimizer hint:
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ALTER SESSION SET optimizer_features_enable = ‘11.2.0.3’;
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In addition to modifying session settings, ALTER SESSION can also be used to set session variables. These variables are user-defined and can be used to store information that is specific to a session. For example, you can set a session variable to store the current user’s name:
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ALTER SESSION SET user_variable = ‘CURRENT_USER’;
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In conclusion, ALTER SESSION is a versatile command in Oracle that allows users to modify session settings for better performance and efficiency. By understanding the various aspects of this command, users can optimize their database sessions and ensure that their queries are executed as intended. Whether you need to change default tablespaces, adjust session-related settings, or enable optimizer hints, ALTER SESSION is a valuable tool in your Oracle database management arsenal.
