Storage Optimization

Starting with IBM Informix Version 11.50.xC4, you can compress data and optimize storage in IDS databases.

Data compression and consolidation methods can minimize the disk space used by your data.

Storage Optimization Methods

• Compressing data - Compresses data in table or fragment rows, reducing the amount of required disk space. After you compress data, you can also consolidate the free space that remains in the table or fragment, and return the free space to the dbspace. Use this method when you want to reduce the size of data in a table . Before you compress a table or table fragment, you can estimate the amount of space you can save if data is compressed. The ratios you display are estimates based on samples of row data. The actual ratio of saved space might vary slightly. The compression ratio depends on the data being compressed. The compression algorithm that IBM Informix uses is a dictionary-based algorithm that performs operations on the patterns of the data that were found to be the most frequent, weighted by length, in the data that was sampled at the time the dictionary was built. A separate compression dictionary exists for each compressed fragment and each compressed non-fragmented table. Each compression dictionary is a library of frequently occurring patterns in the fragment or table data and the symbol numbers that replace the patterns.
  
• Repacking data - Consolidates free space in tables and fragments. Use this method after you compress data or separately when you want to consolidate free space in the table or fragment
  
• Shrinking data - Returns free space to the dbspace. Use this method after you compress or repack data or separately when you want to return free space to the dbspace
  
• Defragmenting table extents - (IDS 11.7 ONLY) Brings data rows closer together in contiguous, merged extents. Use this method when frequently updated tables become scattered among multiple non-contiguous extents.