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Efficient Deletion of a Table Stored in a Segmented Tablespace

IP.com Disclosure Number: IPCOM000035877D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Crus, RA: AUTHOR [+3]

Abstract

Relational data base tables are normally stored in "tablespaces" - one or more areas of physical storage logically concatenated together to form a single linear addressing range (i.e., starting from 0 to 64 gigabytes). The tablespace is divided into uniquely identified pages of fixed size. Segmented tablespaces include a header page, space map pages, and data pages. The data pages store the actual data, while the header and space map pages provide a framework for rapidly accessing the data pages. The data pages are grouped into uniquely identified segments of equal size which form the fundamental unit of storage in the segmented tablespace. All data pages in a given segment contain data for that segment's table only.

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Efficient Deletion of a Table Stored in a Segmented Tablespace

Relational data base tables are normally stored in "tablespaces" - one or more areas of physical storage logically concatenated together to form a single linear addressing range (i.e., starting from 0 to 64 gigabytes). The tablespace is divided into uniquely identified pages of fixed size. Segmented tablespaces include a header page, space map pages, and data pages. The data pages store the actual data, while the header and space map pages provide a framework for rapidly accessing the data pages. The data pages are grouped into uniquely identified segments of equal size which form the fundamental unit of storage in the segmented tablespace. All data pages in a given segment contain data for that segment's table only.

The segments are themselves grouped, and each segment group is preceded by a space map page which contains entries known as segment control blocks for each of the space map page's segments. The segment control blocks for each table are chained together by pointers.

This invention provides a new method for efficiently deleting an entire table (a "mass delete") stored in a segmented tablespace. This method is faster because it does not access, lock, or log the data pages of the table. Instead, the mass delete operation only scans the segment control blocks of the subject table, marking their respective segment status indicators as FREE (deallocated).

The mass delete operation accesses each segment of the table by following the table's chain of segment control blocks. The space map pages are accessed, as required, for each segment of the table.

The example on the next page shows a pseudocode implementation of a mass delete operation.

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It is essential that no other transaction or operation be performed on a table being mass delet...