OVERFLOW control statement

This optional control statement specifies how the overflow area of the prime data set group of an HDAM database or the overflow area of the prime data set group of each partition of a PHDAM database, should be buffered.

The OVERFLOW control statement affects the buffering efficiency for the prime data set group of an HDAM database, or of the prime data set groups of a PHDAM database; especially, it affects both the size of the buffer space and the elapsed time.

The same OVERFLOW statement must be specified for each prime data set group of partitions of a PHDAM database.

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OVERFLOW CAB
         SHR
         BB

Position

Description

1

Code the OVERFLOW keyword to change the OVERFLOW option.

10

Code one of the following three keywords:

CAB

CAB is the default.

CAB specifies that separate CAB buffers are allocated for the root addressable area and the overflow area, respectively. Chained sequential I/O is possible in both areas.

The total number of buffers allocated for the first data set group of HDAM is given by:

      2 x (RANSIZE x (NBRSRAN + 1) + NBRDBUF)

The total number of buffers allocated for the first data set group of a PHDAM database depends on the PARTPROC statement specified for the database.

SHR

SHR instructs CAB to use the same buffer for both the root addressable area and the overflow area.

Chained sequential I/O is possible in both areas.

The number of (shared) buffers allocated for the first data set group of HDAM is:

      RANSIZE x (NBRSRAN + 1) + NBRDBUF

The total number of buffers allocated for the first data set group of a PHDAM database depends on the PARTPROC statement specified for the database.

BB

BB does not allow chained sequential I/O in the HDAM or PHDAM overflow area. If only a small number of I/Os are performed in the overflow area, the OVERFLOW BB option is reasonable.

The OVERFLOW BB option specifies that CAB buffers the root addressable area and that BB buffers the overflow area. No chained sequential I/O takes place in the overflow area.

The OVERFLOW BB option uses less buffer space than the OVERFLOW CAB option. For HDAM, the total number of buffers allocated is the sum of the following:

For the root addressable area,
```
  RANSIZE x (NBRSRAN + 1) + NBRDBUF 
```
For the overflow area,
```
  NBRDBUF 
```

The total number of buffers allocated for the root addressable areas and overflow areas of the first data set group of a PHDAM database depends on the PARTPROC control statement specified for the database.