15.00 - Determining How Much Multi-Value Compression Can Be Realized - Teradata Database

Teradata Database Design

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User Guide

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:

  • Column widths of 2, 4, 8, and 16 bytes.
  • Number of compressed distinct values per column ranging through 1, 3, 7, 15, 31, 63, 127, and 255 (corresponding to the range maxima expressible by 1 to 8 compress bits in the row header)
  • Number of rows with value compressible columns equal to 20, 50, 80, and 100 percent of the cardinality for the table.
  • 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.