Specifies client side network communications links.
If you specify CommLinks=ALL, the client searches for a server using all available communication protocols. Since there may be an impact on performance if you specify CommLinks=ALL, use this setting only when you don't know which protocol to use.
If you specify one or more protocols in the CommLinks (LINKS) connection parameter, the client uses the named communication protocol(s), in the order specified, to search for a network database server. A connection error appears and the connection attempt aborts if the connection fails to connect using a specified protocol, even if there are protocols remaining in the list to try.
If you do not specify a CommLinks (LINKS) connection parameter, the client searches for a server on the current machine only, and only using a shared memory connection. This is the default behavior, and is equivalent to CommLinks=ShMem. The shared memory protocol is used for communication between a client and server running under the same operating system on the same machine.
Available values of the CommLinks parameter are as follows:
SharedMemory (ShMem) – Start the shared memory protocol for same-machine communication. This is the default setting. The client tries shared memory first if it appears in a list of protocols, regardless of the order in which protocols appear.
ALL –Attempt to connect using the shared memory protocol first, followed by all remaining and available communications protocols. Use this setting if you are unsure of which communication protocol(s) to use.
TCPIP – Start the TCP/IP communications link. TCP/IP is supported on all operating systems.
Each of these values can have additional network communications parameters supplied.
You may wish to use a specific protocol, as opposed to ALL, for the following reasons:
The network library starts slightly faster if unnecessary network links are not started.
Connecting to the database may be faster.
You must specify the link explicitly if you wish to tune the broadcast behavior of a particular protocol by providing additional network communications parameters.
Additional network communications parameters may be provided for each link, to tune the broadcast behavior of the link.
The CommLinks parameter corresponds to the database server -x command-line switch. By default, the network server starts all available protocols, which is equivalent to -x ALL. See the -x list start_iq utility startup option in the Utility Guide.
The following connection string fragment starts the TCP/IP protocol only:
CommLinks=tcpip
The following connection string fragment starts the shared memory protocol and searches for the database server over shared memory. If the search fails, it then starts the TCP/IP port searching for the host kangaroo in addition to servers on the immediate TCP/IP network.
CommLinks=tcpip(HOST=kangaroo),shmem