Optimization of the Memory Usage metric for an ApsaraDB RDS for PostgreSQL instance with cloud disks - ApsaraDB RDS

ApsaraDB RDS for PostgreSQL instances with cloud disks run on shared infrastructure that reserves memory for the management system and the operating system. The previous Memory Usage metric measured only PostgreSQL process memory and excluded this overhead, so reported utilization was lower than actual consumption. The updated metric accounts for all memory consumers on the instance, giving you a more accurate view of memory utilization.

What changed

The formula used to calculate memory usage has been updated.

Before:

Memory usage = Memory occupied by PostgreSQL processes
             / Memory purchased for your RDS instance

After:

Memory usage = (Memory occupied by PostgreSQL processes
              + Memory consumed by the management system
              + Memory consumed by the operating system)
             / Memory purchased for your RDS instance

Note

The updated formula also counts the memory reserved for huge pages as part of the memory occupied by PostgreSQL processes.

Effective date

November 30, 2022

Potential impacts

No performance impact. Instance specifications and performance are not affected.
Higher reported memory usage. Because the formula now includes management system and operating system memory, the Memory Usage (%) value will be higher than before the update. This is expected and reflects actual utilization more accurately.
Low available memory on small dedicated instances. After the update, some dedicated RDS instances with small specifications may show low available memory. If this applies to your instance, change the instance type to a general-purpose instance type. For more information, see Change the specifications of an ApsaraDB RDS for PostgreSQL instance.

Where to view the metric

View Memory Usage (%) on the Autonomy Services > Dashboard page in the ApsaraDB RDS console.

For a complementary view, check the db.mem_available.ratio metric in enhanced monitoring. This metric shows the percentage of available database memory. For details, see Use the performance trends feature for an ApsaraDB RDS for PostgreSQL instance and View the enhanced monitoring metrics of an ApsaraDB RDS for PostgreSQL instance.