bdfd1m1lDatabase Administration

Setting Different Sizes for Overflow Blocks

The following scenario addresses setting different sizes for overflow blocks.

Problem

Nearly all (90%) of the subfiles in a file contain about 1200 bytes. The remaining subfiles are much larger, each containing approximately 5000 bytes.

You do not want to allocate 4095-byte overflow blocks because this means that most (90%) of the overflow blocks will have 2895 bytes of wasted DASD space.

Solution

In this example, set the prime block size (&SW00WRS) to L2, the overflow block size (&SW00ARS) to L4, and set &SW00OP1,#BIT5.

The &SW00OP1 indicator tells the TPFDF product to process overflow blocks in an economical way. If the overflow data fits into blocks the same size as the prime blocks (L2), the TPFDF product will use overflow blocks of this size. This is an economical solution for the 90% of the subfiles that contain about 1200 bytes.

If the TPFDF product cannot fit the overflow data into these small blocks, it uses overflow blocks of a size specified by the &SW00ARS set symbol. In this example, the larger subfiles (10%) use 4095-byte blocks (size L4).

DSECT Set Symbols

      &SW00WRS  SETC   'L2'
      &SW00ARS  SETC   'L4'
      &SW00OP1  SETC   '.....1..'      (bit 5 set)

DBDEF Statements

No changes are necessary if the changes are made in the DSECT macro.

Application Coding

Not applicable.