CommLinks Connection Parameter [Links]

Usage

Anywhere

Values

String

Default

Use only the shared memory communications link to connect.

Description

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 do not know which protocol to use.

If you specify one or more protocols in the CommLinks (LINKS) connection parameter, the client uses the named communication protocols, 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:

• 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.

Some of the reasons you may want to use a specific protocol, instead of ALL:

• The network library starts slightly faster if you do not start unnecessary network links.
• Connecting to the database may be faster.
• You must specify the link explicitly 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 iqsrv16 server option. By default, the network server starts all available protocols, which is equivalent to -x ALL.

Examples

• 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