When a search that cannot use a performance-enhancing facility (such as the rapid grouping facility) is being performed, global buffers are accessed roughly the same number of times as the number of rows there are that match the condition. With the snapshot method, the first time data is accessed, all rows in the buffer that match the search condition are copied to process private memory. The second and subsequent times that the same page is accessed, process private memory is referenced, and the search results are returned. This enables search times to be reduced after the first search. It also reduces the number of times that a global buffer is accessed, and avoids concentrating accesses to the same buffer.

Figure 6-12 provides an overview of the snapshot method.

Figure 6-12 Overview of the snapshot method

Specification method

Specify SNAPSHOT (default value) in the pd_pageaccess_mode operand.