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Shadow Table Technique for Removal of Data Archived from a Source Table

IP.com Disclosure Number: IPCOM000022153D
Original Publication Date: 2004-Feb-27
Included in the Prior Art Database: 2004-Feb-27
Document File: 1 page(s) / 52K

Publishing Venue

IBM

Abstract

Certain conditions will warrant the need to remove the inactive data from the source tables not during the archival process, but, at a later time. To insure that only the inactive data archived from the source is removed a shadow table is used as a reference.

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Shadow Table Technique for Removal of Data Archived from a Source Table

DB2 databases containing data considered to be inactive can be identified by a database query predicate. The archival processes uses the query predicate to, first, move the inactive data from a source to a target, then next, to remove the inactive data from the source. Certain conditions will warrant a time lag between the copy of the inactive data from the source and the time the query predicate will be used in the removal of inactive data from the source. Therefore, this technique does not quarantine that only the data that was archived will be the only data removed from the source. The problem with this technique is that data that meets the original selection criteria could be added to the source table between the time the archive action started and the time the data is removed. If this occurs, data not archived could be removed from the source and lost. The solution is the usage of a shadow table. The shadow table contains the unique row identifiers of the archived data. Therefore, when the removal of inactive data from the source is performed, the shadow table is used to reference back to the inactive rows from the source table, see figure 1.

Figure 1 - Shadow table technique

How it works, when an archive action begins, a shadow table is created for each table being archived. Each shadow table is created with a time stamp column. When the selection criteria against the inactive source da...