System of database copy operations using a virtual page control table to map log data into physical store order

摘要

A method for producing a duplication of a database stored in an external storage by writing over copy data of the database with update log data which was acquired after acquisition of the copy data. This method is implemented in a computer system having a virtual storage operating system. The system includes a virtual storage area which is defined as having virtual pages which have a one-to-one correspondence to blocks in an external copy data storage, where the virtual pages are the database copy data is stored and in an order according to physical addresses of the blocks. Each update log data is acquired in units of the blocks. A control table is provided which includes control values which have a one-to-one correspondence to the virtual pages. A control value from the control table is set when the update log data is set to the virtual pages. Repeated operations are made of reading out the update log data from the external log data storage and checking a corresponding control value to see if the control value is set, and setting the control value if it was not set. The control table is then searched in the order of virtual page arrangement and where the control values are set the update log data is read out and is written over the copy data in the external copy data storage. This writing thereby being done in such order that the actuator has a minimal travel distance to a track position of external storage where the copy data is stored.