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Don Burleson Blog 







Multiple instances on a server tips

Oracle Database Tips by Donald BurlesonJuly 23, 2015

Question:  Can Oracle support multiple instances on different releases of Oracle on a single server?

Answer:  Yes, Oracle is designed such that dozens of instances can run on a server, each on a different release of Oracle.  Originally, the 1970's mainframes were designed to support many databases on a single server, so this is not a new concept, and multiple databases on a server is not unique to Oracle.

See here, there benefits of multiple databases per server and these important notes on adding a new instance to an existing Oracle server.

The "one instance, one server" is a leftover from the 1990's days of minicomputers, and today we are seeing massive server consolidation tips with many instances residing on giant million dollar servers with hundreds of gigabytes of RAM.

In 2015 Oracle noted that 99% of OLTP applications have multiple instances per server

Each instance can have it's own unique ORACLE_HOME directory, each with a different release of Oracle, and the oratab file (/etc/oratab, or /var/opt/oratab on Solaris, associates each instance with a distinct Oracle home.

If you have a PC running Windows, there would be separate registry entries for each instances, and the unique registry entries can point to different ORACLE_HOME directories, each with multiple releases of Oracle.

To see how many database cohabit a server, see this script to traverse all instances on an Oracle server.

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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

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