MySQL HeatWave User Guide
MySQL HeatWave supports two string column encoding types:
Variable-length encoding: This is the default encoding type. It applies to string columns by default when tables are loaded with the exception of string columns defined explicitly as dictionary-encoded columns.
Dictionary encoding: This is suited for string columns with a low number of distinct values relative to the cardinality of the table.
To use dictionary encoding, you must define the encoding type explicitly for individual string columns. See Section 5.8.1.4, “Encoding String Columns”.