12.1.1 Overview of pdpgbfon

When a database is accessed, finding the desired target data in a global buffer without having to perform any physical input/output operation is called a buffer hit. When the probability of a buffer hit (buffer hit rate) is high, database access performance is stable. When HiRDB has just started, there is no information about tables and indexes in global buffers, so the buffer hit rate is low, resulting in unstable database access performance.

The global buffer residence utility (pdpgbfon) reads information about tables and indexes into global buffers in advance. If you execute pdpgbfon as soon as HiRDB has started, such as before startup of online jobs, you can expect stable database access performance.

For example, in an environment where all tables and indexes can be read from the database to a global buffer, high-speed database operations can be achieved without any physical input/output operations.

The figure below shows the effects of pdpgbfon.

Figure 12-1 Effects of pdpgbfon

[Figure]

Explanation
When pdpgbfon is not used:
  1. UAP accesses the table.
  2. Page information is read from the table because the global buffer does not contain the page information (physical input/output operation occurs).
  3. The result is returned. Whenever this page information is accessed again subsequently, a table read operation will not be necessary because the page has been read into the global buffer. When page information from another page is accessed, the read operation of step 2 will be required.
When pdpgbfon is used:
  1. pdpgbfon is executed, reading table page information into the global buffer.
  2. UAP accesses the table.
  3. The result is returned without reading the page information from the table because the page information is already in the global buffer. Whenever this table is accessed again subsequently, a read operation on the table will not be necessary (no physical input/output operation will occur).