12.8.1 LRU management methods

There are two LRU management methods:

Organization of this subsection
(1) Independent LRUs for management of reference buffers and update buffers
(2) Batch LRU management of global buffers

(1) Independent LRUs for management of reference buffers and update buffers

With this method, reference buffers and update buffers are managed by independent LRUs.

If a shortage occurs in the global buffers, the least recently accessed reference buffer from among the global buffers is removed from the memory.

(a) Criteria

In the following case, it is preferable for the reference buffer and the update buffer to be managed in separate LRUs:

(b) Notes

If a large amount of update processing occurs, the reference buffer hit rate drops, slowing down retrieval processing.

(c) Specification

SEPARATE is specified in pd_dbbuff_lru_option in the system common definition.

(2) Batch LRU management of global buffers

With this method, the global buffers are managed collectively by one LRU.

If a shortage occurs in the global buffers, the least recently accessed buffer from among the global buffers is removed from the memory.

(a) Criteria

It is beneficial to employ batch LRU management of global buffers in the following case:

(b) Notes
(c) Specification

MIX is specified in pd_dbbuff_lru_option in the system common definition.

The updated output page rate for deferred write trigger is specified in the -w option of the pdbuffer operand in the system common definition.