Oracle databases use two important identifiers: SID (System Identifier) and Service Name. While they are related, they serve different purposes and are used in different contexts. In this tutorial, we will explore the concepts of SID and Service Name, their differences, and when to use each.
What is a SID?
A SID is a unique name that identifies an Oracle database instance. It is used to distinguish between multiple instances running on the same machine. The SID is included in the CONNECT DATA section of the TNSNAMES.ORA file and in the definition of the network listener in the LISTENER.ORA file.
What is a Service Name?
A Service Name is an alias used to connect to an Oracle database instance. It is a descriptive name that can be used to identify a specific database service. Service Names are recorded in the TNSNAMES.ORA file on client machines and can be the same as the SID or a different name.
Key differences between SID and Service Name
The main difference between SID and Service Name is their purpose:
- SID uniquely identifies an Oracle database instance.
- Service Name is an alias used to connect to a database instance.
Another important difference is that a single Service Name can be used to connect to multiple instances, while a SID is unique to each instance.
When to use SID and when to use Service Name
Use the SID when:
- You need to identify a specific Oracle database instance.
- You are working in an environment where load balancing is not configured.
Use the Service Name when:
- You need to connect to a database service that can be provided by multiple instances.
- You want to take advantage of load balancing and high availability features.
Example TNSNAMES.ORA entry
Here is an example of a TNSNAMES.ORA entry that uses both SID and Service Name:
MYINSTANCE, MYINSTANCE.wherever.com =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = myhostname)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = myinstance.wherever.com)
(SID = myinstance)
(SERVER = DEDICATED)
)
)
In this example, the SID is "myinstance", and the Service Name is "myinstance.wherever.com".
Best practices
- Use descriptive and unique names for your SIDs and Service Names.
- Keep your TNSNAMES.ORA file organized and up-to-date.
- Use the correct identifier (SID or Service Name) depending on your specific use case.
By understanding the differences between Oracle SIDs and Service Names, you can better manage your database instances and take advantage of features like load balancing and high availability.