Compression and storage enhancements

Db2 11.5.4 contains additional compression and storage enhancements for column-organized tables that continue to make Db2 an industrial-strength database solution that is suitable for any size of organization..

Attention: The enhancements in this topic are included in the Db2 11.5.4 mod pack release, which is available for the following products:
The following table displays a list of compression and storage enhancements in 11.5.4:
Table 1. Compression and storage enhancements in 11.5.4
Enhancement Description
Improved compression for string data types

For string data types, Db2 now has the ability to use page-based compression algorithms in addition to the existing column dictionary-based compression algorithms. Especially during bulk insert or update operations involving columns that contain many unique values, the compression may be greatly improved for the following data types:

  • CHAR
  • CHAR FOR BIT DATA
  • VARCHAR
  • VARCHAR FOR BIT DATA
  • GRAPHIC
  • VARGRAPHIC
  • BINARY
  • VARBINARY

There are two page-based compression algorithms and Db2 will automatically choose the algorithm that provides the best compression. The first algorithm targets data that has longer repeated patterns, such as text and URLs.

The second algorithm targets data that has 16 or fewer distinct bytes and only short repeating patterns. Such data typically includes the following when stored as strings:
  • Numbers (including decimal, hex, serial numbers, and phone numbers)
  • Dates
  • Times
  • Timestamps

This feature is disabled by default because it is fallback incompatible, and it must be enabled explicitly. For details, see the DB2_COL_STRING_COMPRESSION registry variable.
Reduced Synopsis Table Storage for Small Tables

Synopsis tables for small column-organized tables can have excessive overhead due to Db2's partitioning and storage allocation. The unused allocated storage for synopsis tables can be excessive in comparison to the base tables.

The excessive storage consumption by synopsis tables can be avoided without performance penalty by deferring the creation of synopsis tuples until storage consumption overhead can be minimized.

This feature is disabled by default because it is fallback incompatible, and it must be enabled explicitly. For details, see the DB2_COL_SYNOPSIS_SETTINGS registry variable.
Improved fallback compatibility support

Fallback-incompatible features are the features that, once enabled, will cause the database to be incompatible with any prior release. Because of the fallback impact, those features are now disabled by default to give users more control. Users must make a conscious decision that they will not fallback and explicitly turn on the new features using external registry variables.

After upgrading to the latest release, falling back to a prior release remains a supported operation until the explicit enabling of any fallback-incompatible features.

Once any fallback-incompatible feature is enabled, fallback compatibility is no longer guaranteed. Falling back to an earlier release will likely require restoring the database from a backup from that earlier release.