If the PGA memory used by the instance exceeds the PGA_AGGREGATE_LIMIT parameter, it means that the instance is using more memory for the Program Global Area (PGA) than is allowed. The PGA is a memory area that is used by Oracle to store data and control information for Oracle processes.
There are several possible reasons why the PGA_AGGREGATE_LIMIT might be exceeded:
The value of the PGA_AGGREGATE_LIMIT parameter is too low. You can increase the value of this parameter to allow the instance to use more PGA memory.
The instance is processing a large number of queries or data manipulation language (DML) statements, which is causing the PGA to consume more memory than usual.
The instance is running out of memory and is using the PGA as a temporary storage area. This can happen if the instance is using more memory than is available on the server or if there are other processes on the server that are consuming a large amount of memory.
To resolve this issue, you will need to identify the root cause and take appropriate action. This may involve increasing the value of the PGA_AGGREGATE_LIMIT parameter, optimizing the queries and DML statements being run on the instance, or increasing the amount of memory available to the instance. You may want to consult with a database administrator or Oracle support for further assistance.