Oracle Database is a powerful, scalable, and fast relational database management system. However, it occasionally encounters issues that can hamper performance or even bring the whole system to a halt. One such issue is the ORA-04036 error, which occurs when the PGA_Aggregate_Limit is exceeded. In this guide, we will provide a step-by-step solution to resolve the ORA-04036 error in Oracle instances. ## Table of Contents - [Understanding the ORA-04036 Error](#understanding-the-ora-04036-error) - [Step-by-Step Solution](#step-by-step-solution) - [Step 1: Analyze the Error](#step-1-analyze-the-error) - [Step 2: Determine the Cause](#step-2-determine-the-cause) - [Step 3: Increase the PGA_Aggregate_Limit](#step-3-increase-the-pga_aggregate_limit) - [Step 4: Monitor and Optimize](#step-4-monitor-and-optimize) - [FAQs](#faqs) - [Related Links](#related-links) ## Understanding the ORA-04036 Error The ORA-04036 error occurs when the total memory allocated by all active sessions exceeds the value specified by the PGA_Aggregate_Limit parameter. The PGA, or Program Global Area, is a memory region that holds data and control information for a single Oracle server process. Each server process has its own PGA, and the PGA_Aggregate_Limit parameter sets an upper limit for the total size of all PGAs combined. When the ORA-04036 error occurs, Oracle will terminate the offending session, and the error message will provide information about the session's user, the SQL_ID, and the amount of memory allocated. ## Step-by-Step Solution ### Step 1: Analyze the Error First, you need to examine the ORA-04036 error message to gather information about the problematic session. The error message will contain the following details: - User - SQL_ID - Amount of memory allocated Use this information to further investigate the issue and determine the cause. ### Step 2: Determine the Cause Next, you need to determine the root cause of the ORA-04036 error. Common causes include: - A large sort operation - Excessive use of hash joins - Inefficient use of memory by PL/SQL code - Inadequate PGA_Aggregate_Limit setting To identify the specific cause, review the SQL statements executed by the problematic session and analyze their execution plans. You can use tools such as [Oracle Enterprise Manager](https://www.oracle.com/database/technologies/oem-database-management.html) or [SQL Developer](https://www.oracle.com/tools/downloads/sqldev-downloads.html) to help with this analysis. ### Step 3: Increase the PGA_Aggregate_Limit If your analysis shows that the PGA_Aggregate_Limit setting is inadequate, you can increase its value to resolve the ORA-04036 error. To do so, follow these steps: 1. Connect to the Oracle instance as a user with the ALTER SYSTEM privilege. 2. Execute the following command to increase the PGA_Aggregate_Limit:
ALTER SYSTEM SET PGA_AGGREGATE_LIMIT= SCOPE=BOTH;
Replace `<new_value>` with the desired value for the PGA_Aggregate_Limit. Be cautious not to set the value too high, as it may cause the system to run out of memory. 3. Restart the Oracle instance for the changes to take effect. ### Step 4: Monitor and Optimize After increasing the PGA_Aggregate_Limit, monitor the Oracle instance to ensure that the ORA-04036 error does not recur. You can use tools such as [Oracle Enterprise Manager](https://www.oracle.com/database/technologies/oem-database-management.html) or [SQL Developer](https://www.oracle.com/tools/downloads/sqldev-downloads.html) to track PGA memory usage and performance. Additionally, consider optimizing the SQL statements and PL/SQL code executed by the problematic session to reduce memory usage. Techniques to optimize memory usage include: - Using appropriate join methods - Limiting the number of rows processed - Using bind variables - Implementing pagination ## FAQs ### How can I view the current PGA_Aggregate_Limit setting? You can view the current PGA_Aggregate_Limit setting by executing the following SQL query: ```sql SELECT name, value FROM v$parameter WHERE name = 'pga_aggregate_limit';
What is the default value for PGA_Aggregate_Limit?
The default value for PGA_Aggregate_Limit is the greater of 2 GB, 200% of PGA_Aggregate_Target, or 3 MB times the number of processes (specified by the PROCESSES parameter).
Can I set the PGA_Aggregate_Limit value to unlimited?
No, you cannot set the PGA_Aggregate_Limit value to unlimited. However, you can set it to a very high value, effectively making it unlimited. Be cautious when setting the value too high, as it may cause the system to run out of memory.
What happens if I set the PGA_Aggregate_Limit value too low?
Setting the PGA_Aggregate_Limit value too low can cause the ORA-04036 error to occur more frequently, as the total memory allocated by all active sessions may quickly exceed the limit. It may also lead to poor performance, as Oracle may have to rely on disk-based temporary storage instead of memory for certain operations.
How can I monitor the memory usage of individual sessions?
You can monitor the memory usage of individual sessions by querying the V$SESSION view. The following SQL query will display the current memory usage for each session:
SELECT s.sid, s.username, s.program, m.pga_used_mem FROM v$session s, v$process m WHERE s.paddr = m.addr;