15.00 - Net Capacity Usage for Multi-Value Compression - Teradata Database

Teradata Database Design

prodname
Teradata Database
vrm_release
15.00
category
User Guide
featnum
B035-1094-015K

Net Capacity Usage for Multi-Value Compression

Net capacity usage is a measure of the net savings realized from multi-value compressing column data values.

 

IF the computed value for net capacity usage is …

THEN …

positive

the column is a poor candidate for multi-value compression because it would require more net space to compress the specified value than would be saved in row space.

negative

multi-value compression will produce a net space savings for the column because it reduces the net space used to store the compressed value and recovered row space savings.

Equation 6: Net Capacity Usage for Multi-Value Compression

Calculate the value for net capacity usage with “Equation 7: Net Capacity Usage for Multi-Value Compression With Fallback Not Enabled” on page 727 and “Equation 8: Net Capacity Usage for Multi-Value Compression With Fallback Enabled” on page 728.

Equation 7: Net Capacity Usage for Multi-Value Compression With Fallback Not Enabled

where:

 

This term …

Specifies the number of …

table_header_space

table header bytes used by the compressed column set + 2.

This value indicates the number of additional bytes required in the table header to compress the specified values, nulls, or both.

row_header_space

presence octets (see “Equation 9: Additional Presence Octets” on page 728) in the table.

This value indicates the number of additional bytes required in the row header to compress the specified values, nulls, or both.

row_vacated_space

compressed bytes in the compressed column.

This value indicates the number of bytes in the table saved by compression.

Equation 8: Net Capacity Usage for Multi-Value Compression With Fallback Enabled

If the table has fallback enabled, some of the terms in the equation must be doubled.