Determining How Much Multi-Value Compression Can Be Realized
Percent Multi-Value Compression
You can determine how much multi-value compression can be achieved for a set of parameters by calculating its percent compression. Percent multi-value compression is the savings when considering the compressed size in comparison to the uncompressed size. The following tables show the percent compression for a billion row table along several dimensions:
The row header overhead for multi-value compression can be larger than the savings realized, thus producing a net increase, or expansion, in capacity. In other words, more storage capacity is required to store the presence bits in each row and the compressed data value in the table header than is returned to the available storage pool by compression. This condition is indicated by the MINUS character in the tables.
The multi-value compression savings expressed are for individual columns. Overall system savings are dependent on the number of columns that are compressed and the individual savings realized from each column.