Although Fileshare reduces the number of requests made across the network for COBOL I/O, some types of data file access benefit more than others. The following areas affect Fileshare's ability to improve the speed of accessing remote data:
Where possible, you should use Fileshare in synchronous communications mode (/sc). This has been shown to improve performance significantly when using the CCISM protocol. We recommend that asynchronous mode (that is, Fileshare without the /sc setting) should be considered as being for development purposes only; production installations should always use synchronous mode, if possible.
A single request to an indexed data file can involve many accesses to the physical data file itself such as reading the header and updating the integrity marker. Complex key structures also increase the number of accesses needed to update the index structure in the file. Using the normal COBOL file handling system, each of these accesses generates a request that is sent across the network. Using Fileshare, only one request is sent across the network. The simpler data file organizations (relative and sequential files) involve a smaller processing overhead.
Any speed improvements using Fileshare are therefore more apparent when processing indexed data files.
The number of accesses to a data file needed to process a WRITE, DELETE or REWRITE operation is generally larger than the number needed to process a READ or START operation. Using the normal COBOL file handling system, each of these accesses generates a request that is sent across the network. Using Fileshare, only one request is sent across the network.
Any speed improvements using Fileshare are therefore more apparent when performing WRITE, DELETE or REWRITE operations.
If your program opens a data file exclusively, the normal COBOL file handling system uses caching. This means that it does not have to check to see if the file has been updated on every I/O operation. The number of requests sent across the network, therefore, is significantly less if the data file is opened exclusively.
Fileshare provides a greater improvement in performance, therefore, when a large number of users require concurrent access to data files than when files are opened exclusively. This is because access and caching are controlled by the Fileshare Server and so the additional requests needed when accessing a shared data file via the normal COBOL file handling system are not needed.
Any speed improvements are therefore very specific to individual applications and become more pronounced as more Fileshare Clients concurrently access the same data files.