Shadow Page Mechanism
Original Publication Date: 1986-Jun-01
Included in the Prior Art Database: 2005-Mar-09
This invention relates to a method for improving the performance of shadow page checkpoint by using a page allocation log and a page map block timestamp to reduce the page map and allocation map I/O during checkpoint. The page allocation log allows the updates to the new (post-checkpoint) allocation map to be made without consulting the old page map blocks during checkpoint. The log also permits deferring the updates to the allocation map over several checkpoint intervals. The use of a checkpoint number in the page map blocks allows the system to reset the UPDATED flags in the block on the next reference to the block after the checkpoint instead of during the checkpoint. The method decreases drastically the overhead of checkpoint in a data base system using shadow pages to preserve physical integrity.