Oracle:SID与服务名Service_name区别、本地Net服务名与服务名区别(in Oracle tnsnames.ora)

How SID is different from Service name in Oracle tnsnames.ora：
http://stackoverflow.com/questions/43866/how-sid-is-different-from-service-name-in-oracle-tnsnames-ora

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In short: SID = the unique name of your DB, ServiceName = the alias used when connecting

Not strictly true.. SID = unique name of the INSTANCE (eg the oracle process running on the machine). Oracle considers the "Database" to the be files.

Service Name = alias to an INSTANCE (or many instances). The main purpose of this is if you are running a cluster, the client can say "connect me to SALES.acme.com", the DBA can on the fly change the number of instances which are available to SALES.acme.com requests, or even move SALES.acme.com to a completely different database without the client needing to change any settings.

本地Net服务名 和 service_name 区别图例：