SAP Basis Tech Supports

Symptom

You use 11.50.xC4.
You consider whether or not you want to compress the data of some tables.
Other terms

Compression, extents, performance, reorg, reorganization
Reason and Prerequisites

You use 11.50.xC4 or higher.
The table contains data that can be compressed (no cluster or similar).
Solution

11.50.xC4 provides you with the option of controlling the compression of tables using sysadmin functions:

Activate compressionCompress existing dataUncompress dataMove data to the beginning of the tableRemove freed extentsCalculate current and expected compressionOption: Exclusive lock of table during the conversion

During the conversion, processing is performed in blocks, so it should also work with large tables.
Indexes are not compressed. Only the data is compressed.
During a conversion, the application must be stopped because we do not know whether the temporary existence of duplicate data (that is locked but can be read using “dirty read”, phantom records) in the application can lead to serious, incorrect query results.
The relevant chapters have been inserted in the online documentation for the Informix database on the IBM web site:
http://publib.boulder.ibm.com/infocenter/idshelp/v115/index.jsp
-> Informix SQL -> Guide to SQL: Syntax
-> Built-In Routines -> Compress and Uncompress Operations
Other sites for the topic:
http://www-01.ibm.com/software/data/informix/compression/
The effects on the performance of SAP have not yet been examined. The greatest improvement would be expected for BW applications where the compressed data is read sequentially. A smaller improvement would be conceivable if the data is read according to an index, the sorting of which corresponds with the data (for example, if the table with sorted data has been loaded).
The space saved by well-compressed text data is estimated at 80%. Caution: In some tables, the space used by the indexes is almost as much or is collectively more than the amount of space used by the actual data.