Data Compression in SQL Server

Row Compression Implementation

Enabling compression only changes the physical storage format of the data that is associated with a data type but not its syntax or semantics. Application changes are not required when one or more tables are enabled for compression. The new record storage format has the following main changes:

  • It reduces the metadata overhead that is associated with the record. This metadata is information about columns, their lengths and offsets. In some cases, the metadata overhead might be larger than the old storage format.
  • It uses variable-length storage format for numeric types (for example integer, decimal, and float) and the types that are based on numeric (for example datetime and money).
  • It stores fixed character strings by using variable-length format by not storing the blank characters.

Page Compression Implementation

Compressing the leaf level of tables and indexes with page compression consists of three operations in the following order:

  1. Row compression
  2. Prefix compression
  3. Dictionary compression

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