TempBLCSpread - Analytics Database - Teradata Vantage

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

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.

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