Multiple VSAM strings

As far as concurrent input/output operations with CICS® are concerned, the transient data (TD) programs issue VSAM requests whenever real input/output is required between the buffers and the VSAM TD data sets. The use of multiple VSAM strings enables multiple VSAM requests to be executed concurrently, which in turn leads to faster servicing of the buffers.

VSAM requests are queued whenever the number of concurrent requests exceeds the number of available strings. Constraints caused by this be relieved by increasing the number of available strings, up to a maximum of 255. The limit of 255 on the number of strings should be taken into consideration when choosing the number of buffers. If the number of buffers is more than the number of strings, the potential for string waits increases.

The number of VSAM strings that CICS allocates for TD is specified by the TD system initialization parameter. The CICS default is 3.