11.3 Specifying the prefetch facility

The prefetch facility inputs multiple pages to a global buffer or local buffer in the batch mode.

Organization of this section
(1) Effects of the prefetch facility
(2) Criteria
(3) Specification
(4) Considerations

(1) Effects of the prefetch facility

When a large amount of data is to be retrieved using direct disk accesses (raw I/O), the prefetch facility can reduce the input/output time. This facility is especially effective for retrieving data without using an index or for using an index to search a table that contains many data items in ascending order.

(2) Criteria

The prefetch facility can be used to input multiple pages in the batch mode for the following SQL statements and utility:

(3) Specification

(a) Global buffers

To use the prefetch facility, specify 1 or a greater value in the pdbuffer operand's -m option in the system common definition. Specify the number of pages to be read in batch mode in the pdbuffer operand's -p option.

(b) Local buffers

To use the prefetch facility, use the -p option of the pdlbuffer operand to specify the number of pages for batch input.

(4) Considerations