Oracle HTTP Server B12255-01 Administrator's Manual page 105

Notes:
If the database is running in the same Oracle home, or the environment
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variable "TWO_TASK" is set (called "LOCAL" on Windows NT), this parameter
need not be specified.
If the database is running in a separate Oracle home, then this parameter is
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mandatory.
If you have problems connecting to the database:
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Check the username and password information in the DAD.
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Make sure that you run "tnsping <string>" and execute commands
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such as:
sqlplus DADUsername/DADPassword@<string>
Ensure that TNS_ADMIN is configured properly.
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Verify that the HOST:PORT:SERVICE_NAME format makes the connection
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go through.
Ensure that the TNS listener and database are up and running.
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Ensure that you can ping the host from this machine.
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From a mod_plsql perspective, TNSFormat and NetServiceNameFormat
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are synonymous and denote connect descriptors that are resolved by Net. The
TNSFormat is provided as a convenience so that end-users use this to signify
that the name resolution happens through the local tnsnames.ora. For
situations where the resolution is through an LDAP lookup as configured in
sqlnet.ora, it is recommended that the format specifier of
NetServiceNameFormat be used.
If your database supports high availability, for example, RAC database, it is
highly recommended that you use the NetServiceNameFormat such that the
resolution for the net service name is through LDAP. This enables you to add or
remove RAC nodes accessible through mod_plsql by just changing Oracle
Internet Directory with the new/deleted node information. In such situations,
hard-coding database listener HOST:PORT information in dads.conf or in the
local tnsnames.ora is not recommended.
In older versions of the product, this configuration parameter was called
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connect_string.
Oracle HTTP Server Modules 7-35
mod_plsql