In general, customer-written applications should not use reserved query band names, which are reserved for use by Teradata-written applications and applications written by third party Teradata partners. However, the TVSTemperature query bands are an exception to this rule because they support both Teradata Virtual Storage and temperature-based block-level compression.
Use the TVSTemperature query band for tables whose effective BLOCKCOMPRESSION option is AUTOTEMP. For AUTOTEMP to be active, both BLC and TempBLC must be enabled in DBS Control. In that case the TVSTemperature query band specifies the desired temperature for the table cylinders on which the table data is to be stored. This temperature determines the compressed or noncompressed state of blocks in the table. The DBS Control parameter TempBLCThresh determines which temperatures compress data and which decompress data.
Following are the temperature bands for block-level compression. The percentages are approximate.
|COLD||The 20% of data that is least frequently accessed.|
|WARM||The remaining 60% of data that falls between the COLD and HOT bands.|
|HOT||The 20% of data that is most frequently accessed.|
|VERY HOT||Data that you or Teradata Virtual Storage determines should be added to the Very Hot cache list and have its temperature set to very hot when it is loaded using the TVSTemperature query band.|
You can specify either VERY HOT, HOT, WARM, or COLD for each of these query band names.
These query bands are valid for both sessions and transactions.
See Teradata Vantage™ - Teradata® Virtual Storage, B035-1179 for more information on these query band names.