Purpose
Specifies the percentage above and below the TempBLCThresh setting at which data should be compressed or uncompressed if temperature-based block-level compression (TBBLC) is enabled. For example, if TempBLCThresh is COLD and TempBLCSpread is 5%, the data must be 5% colder than COLD to be compressed and 5% warmer than COLD to be uncompressed.
This setting can be used to prevent data that normally has a temperature close to the threshold from being repeatedly compressed and uncompressed.
Field Group
Compression
Valid Range
1 through 25 percent
Default
5%
Changes Take Effect
After the DBS Control Record has been written.
Usage Notes
BLC enables data compression at the data block (DB) level of the Teradata Database file system. Compression reduces the amount of storage required for a given amount of data. The BlockLevelCompression field of DBS Control enables and disables BLC.
Data temperature refers to the frequency of access. Hot data is frequently accessed. Cold data is infrequently accessed. Warm data is accessed moderately frequently. TBBLC automatically compresses colder data to save storage space, and decompresses the data if it becomes hotter. At any time, different portions of a table, such as different partitions, may exist in different states of compression depending on their temperatures.
Related Topics
| For more information on… | See… |
|---|---|
| Block-Level Compression | Database Design |
| BLOCKCOMPRESSION table attribute | SQL Data Definition Language - Syntax and Examples |
| Enabling TBBLC | EnableTempBLC |
| Ferret COMPRESS, UNCOMPRESS, and FORCE commands | F |
| Query bands for compression | SQL Data Definition Language - Syntax and Examples |
| Storage group of DBS Control fields | Storage Group |