Use a single tnsnames.ora on your Windows PC across 8i, 9i and 10g

One of the problems I have encountered over the years is multiple client versions on Windows machines and multiple tnsnames.ora files.  For example, a PC may have Oracle 8i, Oracle 9i and Oracle 10g clients installed.  Each home will use its own tnsnames.ora file.  This causes lot of confusion and sometimes we don't even know which tnsnames.ora file is being used.

An elegant solution to this problem is the environment variable TNS_ADMIN.  In Windows you can set environment variables by following these steps:

Right click on My Computer

Click on Properties

Click on Advanced tab

Click on Environment variables button.

You can set a new System environment variable called TNS_ADMIN and give the value as a common directory which will contain tnsnames.ora file.  For example TNS_ADMIN=c:\tns

Once you set this variable, irrespective of the Oracle client being used, c:\tns\tnsnames.ora will be the single tnsnames.ora file used to resolve oracle names.