AWS PostgreSQL max_connection per instance type

aws_postgresql_max_connection.md

The default formula use by AWS RDS to calculate the max_connections parameter is: LEAST({DBInstanceClassMemory/9531392},5000)

But It's hard to find the exact value of DBInstanceClassMemory.

So, here are the values I got when I ran the SQL commmand: show max_connections; in some RDS instances:

Instance type	RAM (GB)	max_connections
db.t2.small	2	198
db.t2.medium	4	413
db.t2.large	8	856
db.m4.large	8	856
db.r4.large	15.25	1660

These are default values. You can always change the max_connections value in the parameters group of your DB.

Using describe_db_instances I'm getting the value of db_instance_class which is db.m4.2xlarge.

1. Depends on the value of db_instance_class, is there a way I can directly get the value of max_connections ?
2. There is also another way using describe_db_instances or running below cmd in AWS CLI, I can get the value of max_connections:
   aws rds describe-db-parameters --db-parameter-group-name mdsol-postgres11 --source system which is as below:

{
    "Parameters": [
     ...., 
          {
            "ParameterName": "max_connections",
            "ParameterValue": "LEAST({DBInstanceClassMemory/9531392},5000)",
            "Description": "Sets the maximum number of concurrent connections.",
            "Source": "system",
            "ApplyType": "static",
            "DataType": "integer",
            "AllowedValues": "6-8388607",
            "IsModifiable": true,
            "ApplyMethod": "pending-reboot"
        },
...,

But, now I am not sure what I should pass to LEAST({DBInstanceClassMemory/9531392},5000) how can I can get the value of max_connections as show here

You can use the query below to collect the value that is the result of the equation LEAST({DBInstanceClassMemory/9531392},5000)

select * from pg_settings where name='max_connections';

max_connections is the result of an equation

In some cases, depending on the way your system was built, you may end up reaching 100% CPU usage before you even reach half of the possible connections.
keep your eyes open for this.

Does this LEAST({DBInstanceClassMemory/9531392},5000) apply to graviton instances too. As it seems they support more max connections than the others based on https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/AuroraPostgreSQL.Managing.html but doesn't have data for t4g family.

Graviton - db.r6g.xlarge (32 GB) = 3484. Looks like the same formula.