Specifies conditions under which MANUAL tables have the data blocks (DBs) of permanent data in their primary data subtables compressed by default.
MANUAL tables are those created or altered to have BLOCKCOMPRESSION=MANUAL, or those with BLOCKCOMPRESSION=DEFAULT when the DefaultTableMode DBS Control field is set to MANUAL.
|ALWAYS||The DBs of a new table will be compressed regardless of Query Band options specified at load time.|
|ONLYIFQBYES||The DBs of a new table will not be compressed unless a Query Band used at load time specified to compress them.|
|UNLESSQBNO||The DBs of a new table will be compressed unless a Query Band used at load time specified not to compress them.|
|NEVER||The DBs of a new table will not be compressed regardless of any Query Band used at load time. The Ferret utility COMPRESS command will have no effect.|
Changes Take Effect
After the DBS Control Record has been written.
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.
BLC can be enabled or disabled system-wide, or for various categories of tables. For Permanent data, these include subtables for primary, fallback, eligible LOB data, and join and hash indexes. Secondary indexes on primary rows are never compressed, but fallback copies of secondary indexes can be compressed to save space.