Error connecting DB from DAC ORA-12516: TNS:listener could not find available handler with matching protocol stack

I ran into this error a lot recently when running DAC execution plan, which takes some time to complete. Here is the error details that you can get from Informatica session log when the sessions failed:

RR_4036 Error connecting to database [Database driver error...Function Name : Logon

ORA-12516: TNS:listener could not find available handler with matching protocol stack

Database driver error...

Function Name : Connect

Database Error: Failed to connect to database using user [etldw] and connection string [BIQATST].].

Upon some researching and some help from a great colleague of mine, we decided to change the number of session connections to the Database. This is likely due to the number of connections at Database level not having enough so some of the connection requests get hung.

It is recommended to have about 500 sessions in the DB.

Upon changing the setting and re-running the execution plan, my error messages have gone away.

Thank you