TXSeries Architecture - Fast Local Transport (FLT)

Technote (FAQ)


What is Fast Local Transport (FLT)?


FLT is a mechanism used by SFS to communicate with clients while running on the same host as the SFS. The communication mechanism is through UNIX named pipes. The default place where these pipes are set up is /tmp. (It is possible to where the pipe files are located by using CICS_TK_FLT_PIPE_DIR environment variable.)

FLT is the default communication mechanism when the server and client are on the same host.

If a relatively large number of processes will be using FLT, make sure the number of file descriptors that a process is able to open is appropriate. (The default on Solaris 2.5 is 64 which is not high enough for an SFS serving 15 application servers running on the same host).

To control the number of file descriptors used by FLT on the server side, set the environment variable CICS_TK_FLT_SERVER_MAX_FDS to the maximum number of file descriptors permitted to be used for FLT. If this environment variable is set to 0, the effect is to turn off FLT.

To control the use of FLT on just one client process, set the environment variable CICS_TK_FLT_CLIENT_MAX_FDS to 0 for that specific process.

It is a reasonable troubleshooting step to turn off FLT on either the server or the client (depending on the hypothesis being tested) to determine if the problem disappears.

It is recommended to do performance comparisons with applications using FLT and then without using FLT to determine any performance gains associated with FLT before committing to using it. If planning to restrict the transport to UDP only, then be sure to compare performance with FLT and without FLT while the UDP restrictions are turned on. (FLT introduces a potential for failures that should be weighed against the performance gain it provides. For a given application the performance gain may be so slight as to not warrant its use.)

On AIX there is a fast mechanism for SARPC traffic between a client and server on the same host. Run performance tests to make sure using FLT is faster than using the native SARPC transport on AIX hosts.


Document information

More support for:

TXSeries for Multiplatforms

Software version:

6.0, 6.1, 6.2, 7.1

Operating system(s):

AIX, HP Itanium, HP-UX, Solaris

Reference #:


Modified date:


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