These restrictions apply:
- You cannot write your own compression functions to perform algorithmic compression on JSON type columns. However, Teradata provides the JSON_COMPRESS and JSON_DECOMPRESS functions that you can use to perform ALC on JSON type columns.
- You cannot write your own compression functions to perform algorithmic compression on DATASET type columns. However, Teradata provides the SNAPPY_COMPRESS and SNAPPY_DECOMPRESS functions that you can use to perform ALC on DATASET type columns.
- You cannot use ALC to compress temporal columns:
- A column defined as SYSTEM_TIME, VALIDTIME, or TRANSACTIONTIME.
- The DateTime columns that define the beginning and ending bounds of a temporal derived period column (SYSTEM_TIME, VALIDTIME, or TRANSACTIONTIME).
You can use ALC to compress Period data types in columns that are nontemporal; however, you cannot use ALC to compress derived period columns.
- You cannot specify multivalue or algorithmic compression for a row-level security constraint column.
You can apply algorithmic compression to referential integrity columns.
Referential integrity is supported only on the Block File System on the primary cluster, not on the Object File System.
Depending on the implementation, algorithmic compression can be either physical or logical, though most implementations use physical data compression. Algorithmic compression can be either lossy or lossless, depending on the algorithm used.