Page-Level Compression

Extracting repetitive information from variable-length byte strings and replacing them with shorter symbols.

When you insert a new row into a data page, Adaptive Server compares the data in the columns with the symbols in the page dictionary. If it finds a match in the dictionary for the new data, Adaptive Server stores the dictionary symbol instead of the data, and the row is compressed. When Adaptive Server retrieves the data, the symbol indicates the appropriate data. A page dictionary can include multiple entries, each with a different symbol that compresses a different piece of information.

Extracting and removing short, duplicate values that use fixed-length columns from the rows.

If a fixed-length column includes a high number of duplicates, Adaptive Server stores the duplicate value in the page index, and uses a status bit in the row to indicate that this value is stored in the page index and is available for compression. When you retrieve data from the row, the status bit indicates the value that Adaptive Server includes in the result set.

A page index may contain multiple entries for different duplicate values in the page.

create table order_line (
   order_id int,
   disp_id tinyint,
   width_id smallint,
   number tinyint,
   info_id int,
   supply smallint,
   delivery datetime,
   quantity smallint,
   amount float,
   dist_info char(24))
lock datapages

682, 1, 7, 11, 30000, 7, 'Dec 2 2008 1:19PM', 5, 290, 'Houston')
748, 1, 7, 12, 93193, 7, 'Sep 27 2009 1:15PM', 5, 9900, 'Bakersfield')
239, 1, 7, 13, 50383, 7, 'Aug 18 2008 11:47AM', 5, 8480, 'Modesto')
594, 1, 7, 14, 70901, 7, 'Aug 19 2008 10:37AM', 5, 84840, 'Houston')
849, 1, 7, 1, 3459, 7, 'July 10 2010 3:15PM', 5, 940, 'Alberta')
994, 1, 7, 2, 1232, 7, 'Jan 3 2010 2:15PM', 5, 848, 'Sonoma')
219, 1, 7, 3, 55341, 7, 'Feb 12 2008 9:26AM', 5, 4884, 'Vallejo')
004, 1, 7, 4, 98313, 7, 'Jan 19 2007 2:05PM', 5, 4484, 'Houston')
229, 1, 7, 5, 1347, 7, 'Aug 8 2009 3:37PM', 5, 448, 'Bakersfield')
394, 1, 7, 6, 51276, 7, 'Nov 10 2009 1:38PM', 5, 4473, 'Napa')
119, 1, 7, 1, 18089, 7, 'Oct 29 2009 12:56PM', 5, 312, 'Los Angeles')
938, 1, 7, 2, 38396, 7, 'June 1 2009 3:46PM', 5, 2248, 'Houston')

The disp_id, width_id, supply, and quantity columns all contain duplicate values (1, 7, 7, and 5), that are all short fixed-length columns, and candidates for page index compression.