in ADW, The tnsnames.ora file provided with the credentials zip file contains three database service names identifiable as high, medium, and low. The predefined service names provide different levels of performance and concurrency for Autonomous Data Warehouse.
high: The High database service provides the highest level of resources to each SQL statement resulting in the highest performance, but supports the fewest number of concurrent SQL statements. Any SQL statement in this service can use all the CPU and IO resources in your database. The number of concurrent SQL statements that can be run in this service is 3, this number is independent of the number of OCPUs in your database.
medium: The Medium database service provides a lower level of resources to each SQL statement potentially resulting a lower level of performance, but supports more concurrent SQL statements. Any SQL statement in this service can use multiple CPU and IO resources in your database. The number of concurrent SQL statements that can be run in this service depends on the number of OCPUs in your database.
low: The Low database service provides the least level of resources to each SQL statement, but supports the most number of concurrent SQL statements. Any SQL statement in this service can use a single CPU and multiple IO resources in your database. The number of concurrent SQL statements that can be run in this service can be up to 300 times the number of OCPUs.
The predefined service names provide different levels of performance and concurrency for Autonomous DB Choose whichever database service offers the best balance of performance and concurrency.
Use the low database service name. to minimize the impact of their SQLs to by low consumer group