Specifies the temperature at and below which data blocks are automatically compressed if temperature-based block-level compression (TBBLC) is enabled.
|COLD||Only COLD data is compressed by TBBLC. By default, cold data is the least frequently accessed 20% of data.|
|WARM||WARM and COLD data is compressed by TBBLC.|
|HOT||All data is compressed by TBBLC.|
Changes Take Effect
After the DBS Control Record has been written.
Tables using TBBLC are those having the BLOCKCOMPRESSION table attribute set to AUTOTEMP.
Data temperatures refers to frequency of access:
- Hot data is frequently accessed.
- Cold data is infrequently accessed.
- Warm data is accessed moderately frequently.
Data temperature is measured separately for each AMP at a cylinder level and is a relative measure because the temperature of cylinders can change even if the data it is not directly accessed. This is because it depends on how often other cylinders are accessed in comparison. TBBLC automatically compresses cold data to save storage space and decompresses Warm or Hot data if it was previously Cold (and thus compressed). At any time, different portions of a table, which are spread among many cylinders, may exist in different states of compression depending on their temperatures.
BLC enables data compression at the data block (DB) level of the 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.
When changed, causes TBBLC to immediately start a new cycle.
|For more information on…||See…|
|Block-level compression||Teradata Vantage™ - Database Design, B035-1094.|
|BLOCKCOMPRESSION table attribute||Teradata Vantage™ - SQL Data Definition Language Syntax and Examples, B035-1144.|
|Ferret COMPRESS, UNCOMPRESS, and FORCE commands||Ferret Utility (ferret).|
|Query bands for compression||Teradata Vantage™ - SQL Data Definition Language Syntax and Examples, B035-1144.|
|Storage group of DBS Control fields||Storage Group.|