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Replicating a database by the sequential application of hierarchically sorted log records

  • US 5,530,855 A
  • Filed: 10/13/1992
  • Issued: 06/25/1996
  • Est. Priority Date: 10/13/1992
  • Status: Expired due to Fees
First Claim
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1. In a transaction processing system including at least one active computer system in communication with a backup computer system, the backup computer system having a processor (CPU), memory, and a data storage device having a backup database stored therein, each active computer system having a processor, memory, at least one data storage device having an active database stored as a plurality of data records organized by offset location within blocks in the active system storage device, and redo log records representing changes to be made to a database as part of a database transaction when the database transaction is committed, a computer implemented tracking method for updating the backup database to make it consistent with the active database, comprising the steps of:

  • a) receiving redo records transmitted from the active system into a dataspace work area in the backup system memory;

    b) grouping redo records in the work area from an uncommitted database transaction together;

    c) when a transaction becomes a committed transaction, sorting the redo records for the committed transaction with redo records for other committed transactions in the work area according to database, block number within a database, offset location within a block, and sequence of occurrence;

    d) reading into a buffer in the backup system memory, a plurality of update blocks from the backup database;

    e) sequentially applying sorted committed redo records to corresponding data records in the update blocks; and

    f) immediately writing the update blocks back to the backup database after the sorted committed redo records for the update blocks have been applied to the corresponding data records in the update blocks.

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