CommLinks connection parameter [LINKS]

Specifies client-side network protocol options.

Usage

Anywhere. The CommLinks (LINKS) connection parameter is optional for connections to a personal server, and required for connections to a network server.

Values

String

Default

Use only the shared memory communication protocol to connect.

Remarks

If you do not specify a CommLinks (LINKS) connection parameter, the client searches for a server on the current computer only, and only using a shared memory connection. This is the default behavior, and is equivalent to CommLinks=ShMem. The shared memory protocol is the fastest communication link between a client and server running on the same computer, as is typical for applications connecting to a personal database server.

For information about securing shared memory connections on Unix, see Security tips.

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. Note that if shared memory is specified, an attempt to connect using shared memory is made first, and then the remaining communication protocols are tried in the order in which they are specified. 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.

CommLinks (LINKS) connection parameter values are case insensitive, and include:

  • SharedMemory (ShMem)   Start the shared memory protocol for same-computer communication. This is the default setting. The client tries shared memory first if it is included 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 communication protocols. Use this setting if you are unsure of which communication protocol(s) to use.

  • TCPIP (TCP)   Start the TCP/IP communication protocol. TCP/IP is supported on all operating systems. A personal database server is not autostarted if the CommLinks [LINKS] parameter includes TCPIP.

Each of these values can have additional network protocol options supplied.

See Network protocol options.

You may want to use a specific protocol, as opposed to ALL, for the following reasons:

  • The network library starts slightly faster if the client uses only necessary network protocols.
  • Connecting to the database may be faster.
  • You must specify the protocol explicitly if you want to tune the broadcast behavior of a particular protocol by providing additional network protocol options.

The CommLinks (LINKS) connection parameter corresponds to the database server -x option.

See also
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 protocol and searches for the server on the local network. 

CommLinks=tcpip,shmem

The following connection string fragment starts the shared memory protocol and searches for the server over shared memory. If the search fails, it then starts the TCP protocol and searches for the server on the local network, as well as the host kangaroo. Note that if the server is found over shared memory, the TCP link is not started. 

CommLinks=shmem,tcpip(HOST=kangaroo)
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