When a resource pool is built, the buffers in each buffer pool are numbered from 1 through the number of buffers in each buffer pool. At a given time, several buffers in a buffer pool may hold the contents of control intervals for a particular data set. These buffers may or may not contain RBAs of interest to your processing program. The SCHBFR macro lets you find out. Specify in the ARG parameter of the RPL that defines SCHBFR the address of an 8-byte field that contains the first and last control interval RBAs of the range you are interested in.

Note: For compressed format data sets, the RBA of the compressed record is unpredictable. The RBA of another record or the address of the next record in the buffer cannot be determined using the length of the current record or the length of the record provided to VSAM.

The buffer pool to be searched is the one used by the data component defined by the ACB to which your RPL is related. If the ACB names a path, VSAM searches the buffer pool used by the data component of the alternate index. (If the path is defined over a base cluster alone, VSAM searches the buffer pool used by the data component of the base cluster.) VSAM begins its search at the buffer you specify and continues until it finds a buffer that contains an RBA in the range or until the highest numbered buffer is searched.

For the first buffer that satisfies the search, VSAM returns its address (OPTCD=LOC) or its contents (OPTCD=MVE) in the work area whose address is specified in the AREA parameter of the RPL and returns its number in register 0. If the search fails, Register 0 is returned with the user specified buffer number and a one-byte SCHBFR code of X'0D'. To find the next buffer that contains an RBA in the range, issue SCHBFR again and specify the number of the next buffer after the first one that satisfied the search. You continue until VSAM indicates it found no buffer that contains an RBA in the range or until you reach the end of the pool.

Finding a buffer that contains a desired RBA does not get you exclusive control of the buffer. You may get exclusive control only by issuing GET for update. SCHBFR does not return the location or the contents of a buffer that is already under the exclusive control of another request.