- They cycle of decompressing and recompressing required to access and store data may significantly increase CPU usage compared to uncompressed data.
- Storing data in dense, compressed form may reduce I/O requirements.
For details about compression methods, see Teradata Vantage™ - Database Design, B035-1094.
Multivalue Compression (MVC)
MVC compresses recurring values within a column into a single value in the table header.
MVC enhances the performance of high data volume applications, like call record detail and click-stream data, and provides significant performance improvement for general ad hoc workloads and full-table scan applications
Smaller physical row size results in less data blocks and fewer I/Os and improved overall performance, depending upon amount of compression achieved.
Select and delete operations show a proportionate improvement in all cases. Inserts and updates show mixed results. The load utilities benefit from the compressed values.
Algorithmic Compression (ALC)
- Teradata-supplied UDFs to compress various types of character data
- The ability to create custom UDF algorithms
Teradata-standard ALC UDFs tend to reduce I/O, but can increase CPU usage. For information on the compression/decompression functions, see Teradata Vantage™ - SQL Operators and User-Defined Functions, B035-1210.
BLC compresses data at the data block level.
Because BLC is CPU-intensive, consider the CPU capabilities of the particular Vantage platform when using BLC.
- Apply BLC to all allowable types of data.
- Load and access data at any time because there is enough available CPU to frequently decompress data
- Load tables during off-peak hours.
- Limit access to compressed tables during critical throughput periods.
Some operations (including queries, insert/updates, and CheckTable) can use considerably more CPU while operating on compressed tables. Unless the system is very CPU rich, these operations can impact other workloads and lengthen elapsed response times.