MySQL HeatWave User Guide
Dictionary encoding (SORTED) has the
following characteristics:
Best suited to string columns with a low number of distinct values relative to the cardinality of the table. Dictionary encoding reduces the space required for column values on the MySQL HeatWave nodes but requires space on the DB System node for dictionaries.
Supports GROUP BY and ORDER
BY operations on string columns.
Supports a subset of the operations supported by
variable-length encoding such as
LIKE with prefix expressions,
and comparison with the exact same column.
Dictionary-encoded columns cannot be compared in any way
with other columns or constants, or with other
dictionary-encoded columns.
Does not support:
JOIN operations
LIKE predicates.
Operations that use string operators. Queries that use string operators on dictionary-encoded string columns are not offloaded.
Comparison with variable-length encoded columns.
The dictionaries required to decode dictionary-encoded string columns must fit in DB System node memory. Dictionary size depends on the size of the column and the number of distinct values. Load operations for tables with dictionary-encoded string columns that have a high number of distinct values can fail if there is not enough available memory on the DB System node.
Learn more about Column Limits.