This section summarizes the benefits, best uses, and restrictions of autocompression in Vantage.
Benefits of Autocompression
- Default for column partitions. If you change the default to NO AUTO COMPRESS or you specify NO AUTO COMPRESS for the column partitioning, you can specify AUTO COMPRESS for a column partition to have that column partition autocompressed.
- Vantage can choose to apply multiple autocompression methods from a list of available techniques depending on their effectiveness for a given column partition (there are no available techniques for column partitions with ROW format).
- Reduces I/O overhead if the data can be compressed.
- Vantage must decompress only autocompressed column partition values that are accessed, and decompression is automatically done with typically little performance overhead when values are retrieved.
- Easily combined with null, multivalue, algorithmic, row, block-level, and temperature-based block-level compression.
- Has no effect on table header size.
Best Use of Autocompression
- Column partitions with a single column and COLUMN format
Restrictions and Limitations of Autocompression
- There is typically minimal CPU overhead in determining whether to compress a physical row and if so, what compression techniques to use.
You can eliminate this overhead by specifying NO AUTO COMPRESS (or changing the default to NO AUTO COMPRESS) for a column partition or the column partitioning, which eliminates autocompression for that column or column partition.
- There is additional CPU overhead when you insert rows into a column-partitioned table that uses autocompression.
- If you specify autocompression, Vantage may not apply user-specified MVC or algorithmic compression if they do not further reduce storage space.
- Autocompression techniques are not applied to a column partition with ROW format, even when AUTO COMPRESS is the default for the column partition or explicitly specified.