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

  • US 5,321,832 A
  • Filed: 05/22/1990
  • Issued: 06/14/1994
  • Est. Priority Date: 05/26/1989
  • Status: Expired due to Term
First Claim
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1. A method of producing a duplication of a database having a writing step, in which copy data of said database in an external copy data storage are written over by update log data from an external log data storage, where the update log data was acquired after acquisition of said copy data, the method comprising the steps of:

  • (a) defining a virtual storage area which comprises virtual pages which have a one-to-one correspondence to blocks in said external copy data storage, and where the virtual pages are arranged in an order according to physical addresses of said blocks to which they correspond;

    (b) defining a control table, which includes control values which have a one-to-one correspondence to said virtual pages, and where a control value of the control values will be set when the update log data is set to a corresponding virtual page;

    (c) repeating the substeps of;

    (i) reading out the update log data acquired in units of said blocks from said external log data storage;

    (ii) checking said control value corresponding to the virtual page which corresponds to one of said blocks of copy data to be replaced by said update log data andwhen the control value has not been set, assigning a real storage for the virtual page and storing said update log data to said real storage assigned thereto, and setting the control value,when the control value has already been set, updating the real storage assigned for the virtual page with said update log data; and

    (d) searching said control table in the order of virtual page arrangement and repeating the substep of;

    (i) when said control value is set, reading out the update log data in said real storage and writing over said copy data in said external copy data storage with said update log data, and resetting said control value.

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