15.00 - Block-Level Compression and Tables - Teradata Database

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Block‑Level Compression and Tables

Tables can be block compressed or not, depending on the settings of the DBS Control compression tunables or whether they have been compressed or decompressed using the Ferret utility. See Utilities: Volume 1 (A-K) for information about the DBS Control and Ferret utilities and for information about how the block compression tunables interact with other DBS Control file system tunables.

All limits on data block sizes apply to the uncompressed size of a table. Block compression does not raise any of these limits, nor does it enable more data to be stored in a single data block than can be stored in an uncompressed data block of the same size.

Whether volatile table and global temporary table files are compressed or not depends on whether the Optimizer caches the relation in the request cache (see SQL Request and Transaction Processing). If a relation is cached, it is not compressed. If it is not cached, then it is compressed.

You can combine multi-value compression, algorithmic compression, and block‑level compression for the same table to achieve better compression, but as a general rule you should not use algorithmic compression with block‑level compression because of the possibility of a negative performance impact for other workloads.