Vault database(postgres) secret backend connection: max_open_connections w/ value zero

at here: Specifies the maximum number of open connections to the database. the the max_open_connections parameter have a default value of 4.

But how about the parameter is set to have value ZERO, or -1, what does the two values mean? does it mean no constraints, and we can have infinite number of open connections (from vault to the particular database secrets backend)?

I’ve this question come into mind, b/c when I terraform plan with an way-old terraform state file, for the terraform resource vault_database_secret_backend_connection. terraform reports the odd changes/diff:

max_open_connections: 0 ==> 4

I checked the database secrets backend on vault, the current value is 4,

I also checked our terraform code, and there was no settings of ‘zero’ at the very beginning for the TF resource, though, in the state file it does have line below:


“max_open_connections”: 0,

Questions:

Is the "max_open_connections": 0 generated by old Terraform vault providers by default?
I tried to remove that line from terraform state file and run terraform plan again, it still reports the same diff/changes max_open_connections: 0 ==> 4,

Got pretty confused, please help clarify,