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DFSDVBH0

DFSDVBH0 is the DL/I Buffer Handler Router. All requests for buffer handling services are routed through this module. Depending on the type of request, this module might invoke the OSAM buffer handler (DFSDBH10), the VSAM buffer handler (DFSDVSM0), the OSAM sequential buffering handler (DFSSBCI0), or a combination of these modules. For example a request to retrieve a specific buffer would be routed to the specific buffer handler. A request to invalidate all buffers in a block level data sharing environment would go to all buffer handlers.

DFSDVBH0 processes requests for buffer handler statistics. It will gather the statistics from the individual buffer handlers and return them to the caller. If requested, it will format the statistics in printed report format.

DFSDVBH0 also catches runaway calls in a region that has had a /STOP REGION ABDUMP command issued for it.

Hints

The amount of work DFSDVBH0 does depends on the calling and I/O patterns of the individual job or transaction. In a batch or BMP job it is not unusual for 5% to 10% of the CPU to be in this module.

If a more detailed analysis is desired, it is probably easiest to analyze the individual buffer handlers and find out what work they are doing. Specify Detail for DFSDVSM0 and DFSDBH10 to identify the specific subroutines that are being used the most.

A complete list of functions performed by the buffer handlers and router can be found in the PST field PSTFNCTN, values x'DB' through x'FF.

Reference Sources

More information is available in the IMS DBSOURCE Library Data Set. See your IMS systems programmer.