RE: local connections fail, but listener connections succeed

From: Iggy Fernandez <>
Date: Tue, 8 Jan 2013 16:22:35 -0800
Message-ID: <BLU165-W40D3F36F0A2F26421894AEB2B0_at_phx.gbl>

As an academic exercise to prove the point, I wrote a demonstration to create two instances with the same ORACLE_SID on one Unix server. See Each instance will use a different logical value (soft link) of ORACLE_HOME but both values link to the same underlying physical ORACLE_HOME. The databases that these instances connect to will also have the same db_name (orcl) but a different db_unique_name (orcl1 and orcl2).
> From:
> Here is what happens in a Unix environment. I'm sure there is a close parallel in a Windows environment.> When the Oracle instance is started, an "shmid" for the shared memory segment (SGA) is constructed using the values of the environment variables ORACLE_SID and ORACLE_HOME as inputs. To attach to the shared memory segment subsequently, any slave process needs to reconstruct the shmid of the shared memory segment and to do this it must use the same values of ORACLE_SID and ORACLE_HOME as were used to start the Oracle instance. It is not enough to use the same value of ORACLE_SID. It must also use the same value of ORACLE_HOME.

> > From: SUzzell_at_MICROS.COM
> > This is backwards enough that I don't quite know where to start with it. This morning we noticed that for one environment, we cannot make direct local connections... but we can connect to our hearts' content via the listener. I'm used to seeing the listener act up and being able to connect directly but not via the listener - not this.

Received on Wed Jan 09 2013 - 01:22:35 CET

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