What is the difference? Oracle TNS SID Listener

Question

In human language: What is the difference between: TNS, SID and a Listener? Thanks!

Answer 1

SID aka ORACLE_SID identifies the processes running an instance for the database. It is a physical kind of identifier. RAC databases typically have multiple instances and there for use multiple ORACLE_SID's. SID's can be used to connect to the specified database instance. If that instance is down, the connection fails.

SERVICE_NAME is a logical identifier where clients can connect to, instead of connecting to a SID. Especially in a RAC database, it can happen that a service is running on only a subset of the instances of the database. When using services, the application does not need to know on which ORACLE_SID the requested service is provided. Also, with services you can limit access to your database by disabling a service during maintenance. The ORACLE_SID is always available and can only be put in a restricted mode, limiting all access to the full instance. When an application uses services and as long as at least one instance is serving the service_name, a connection to that service succeeds.

TNS Tranparent Network Substrate, a location transparent and protocol independent network technology. The location transparency is made by using services and in the database a combination of synonyms and database links.

Answer 2

SID: Site Identifier: The Unique name of your database. +/- database instance with multiple databases running on that instance.

Service Name: Alias to an instance (SID)

TNS: Transparent Network Substrate: Oracle relies on TNS to provide network connectivity between Oracle databases, regardless of underlying protocols. This is an oracle network technology that is user-transparent.

Answer 3

These 3 are completely different things in Oracle terms: - Transparent Network Substrate (TNS) is an Oracle networking technology that provides generic network connectivity between Oracle databases and Oracle clients, regardless of underlying protocols (TCP, etc.) - SID - Oracle System Identifier that represents a unique name for an Oracle database instance on a specific host. A standalone database has one SID and it's usually but not necessarily identical to a database name. in RAC database every database instance has its own SID. - Listener - A process that listens for incoming client connection requests and manages network traffic to the database.