Buffer Management › Using Read and Write Drivers

Using Read and Write Drivers

Read Drivers

A read driver performs "look-ahead" reads when CA IDMS/DB is instructed to sweep an area. When it is activated, it uses chained reads to read a track of pages beginning with the third or fourth tracks from the start of the area sweep and attempts to prefetch the pages that will be needed by the application. Use the DCMT VARY DB READ ON/OFF command to activate or de-activate the read driver for an area.

Write Drivers

A write driver facilitates writing pages from the buffer to disk. CA IDMS/DB invokes a write driver under these conditions:

• When a transaction is committed and the buffer contains at least five updated pages. The driver writes all the pages in the buffer updated by the transaction.
• When more than 75% of the pages in the buffer are updated pages.

Use the DCMT VARY DB WRITE DRIVER ON/OFF command to activate or de-activate the write driver.