Flushing a SQL Statement from the Shared Pool in Oracle 12c

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Welcome to the world of Oracle Database! In this article, we will discuss how to flush a single SQL statement from the shared pool. Sometimes, we come across issues where the execution plan for a particular query is not optimal. In such cases, we can tune the plan or create a base plan and forcefully run or flush the SQL statement from the shared pool.

To begin, you need to connect to the database and access the V$SESSION view. This view provides information about the currently active sessions. You can find the specific SQL ID that you want to flush from the shared pool. The SQL ID is a unique identifier assigned to each SQL statement.

Next, you need to identify the hash value of the SQL query. The hash value represents the execution plan number for the specific query. To find the hash value, you can use the V$SQLAREA view. This view contains the address and hash value for each SQL statement in the shared pool. You can select the address and hash value from the V$SQLAREA view where the SQL ID matches the SQL ID of the query you want to flush.

Once you have the hash value and address of the SQL statement, you can proceed to flush it from the shared pool. To do this, you can execute the DBMS_SHARED_POOL.PURGE procedure. This procedure takes the hash value and address as parameters. By running this procedure, you force the removal of the SQL statement from the shared pool.

After executing the purge procedure, you should check if the execution plan still exists for the particular SQL ID. This can be done by querying the V$SQLAREA view again. If no rows are selected, it means the SQL statement has been successfully flushed from the shared pool.

It is important to note that flushing a SQL statement from the shared pool should be done with caution. This action can have an impact on the performance of the system, and it is recommended to only flush statements that are causing significant issues and after analyzing the potential consequences.

In conclusion, flushing a SQL statement from the shared pool in Oracle 12c can be a useful technique in optimizing query performance. By following the steps mentioned above, you can identify and flush a specific SQL statement that is not performing well. However, it is important to exercise caution and analyze the potential impact before flushing any SQL statement from the shared pool.

Thank you for reading this article, and we hope you found it helpful in understanding how to flush a SQL statement from the shared pool in Oracle 12c.