ORA-4036 "PGA memory used by the instance exceeds PGA_AGGREGATE_LIMIT" (Doc ID 2854122.1)

Last updated on FEBRUARY 19, 2025

Applies to:

Symptoms

In Oracle 12c introduced new parameter PGA_AGGREGATE_LIMIT to allow database administrators to limit the aggregate PGA (Program Global Area) memory usage.
By setting the above parameter you will enable a hard limit on PGA usage. If the pga_aggregate_limit value is exceeded, Oracle database will
aborts or terminates the sessions or processes that are consuming the most untunable PGA memory.

In Oracle release 18c and above, The MGA (Managed Global Area) is accounted for out of the PGA.
What this means in practical terms is that the PGA size must be increased in 18c and above versions to accommodate the MGA.
The PGA memory allocation which has required the pga_aggregate_limit to be large enough to handle the MGA also.

Connected processes will not free up space allocated to them back to the Operating System until they are disconnected. This is an expected behavior.
The PGA exists for the lifetime of the process. It can grow if required during runtime.
That is, more memory may be allocated to it by the Operating System if needed, for instance, for a large sort.
However, the PGA will not shrink and deallocate memory back to the OS. Any memory freed up within
the PGA (for instance, after a large sort completes) remains allocated to that process for future use.

Changes

Cause

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