SEQBUFS parameter of DBURTBL macro is used to define the buffers that are used by applications exploiting the sequential read-ahead processing.
Q1: Where are these buffers allocated? In MUF address space?
Q2: When the sequential batch job completes, is the memory for the sequential buffers released to operating system?
Q3: Is there a limit somewhere for the use of these buffers?
A1: In 14.0 (and 15.0) SEQBUFs are allocated by DB Memory Manager in 31-bit region memory of the MUF address space. In 15.1, they are allocated in 64-bit memory of the MUF address space.
A2: When an application using SEQBUFs ends, the SEQBUFs memory is kept in the MUF address space, but made available for other purposes. The memory is NOT returned to z/OS.
A3: Each application can allocate up to 128 SEQBUFs via the URT. There is no limit for the number of applications allocating SEQBUFs other than the region size (14.0 and 15.0), i.e. MUF can run out of 31-bit memory if too many SEQBUFs are in use simultaneously by too many applications (batch jobs).