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MySQL HeatWave User Guide  /  ...  /  String Column Encoding

2.15.3 String Column Encoding

  • To identify explicitly encoded string columns in tables on the MySQL DB System, query the COLUMN_COMMENT column of the INFORMATION_SCHEMA.COLUMNS table. For example:

    mysql> SELECT COLUMN_NAME, COLUMN_COMMENT 
              FROM INFORMATION_SCHEMA.COLUMNS
              WHERE TABLE_NAME LIKE 'orders' AND COLUMN_COMMENT LIKE '%ENCODING%';
    +-----------------+------------------------------+
    | COLUMN_NAME     | COLUMN_COMMENT               |
    +-----------------+------------------------------+
    | O_CLERK         | RAPID_COLUMN=ENCODING=SORTED |
    | O_ORDERPRIORITY | RAPID_COLUMN=ENCODING=SORTED |
    | O_ORDERSTATUS   | RAPID_COLUMN=ENCODING=SORTED |
    | O_CLERK         | RAPID_COLUMN=ENCODING=SORTED |
    | O_ORDERPRIORITY | RAPID_COLUMN=ENCODING=SORTED |
    | O_ORDERSTATUS   | RAPID_COLUMN=ENCODING=SORTED |
    +-----------------+------------------------------+

    You can also view explicitly defined column encodings for an individual table using SHOW CREATE TABLE.

  • To view the dictionary size for dictionary-encoded columns, in bytes:

    mysql> USE performance_schema;
    mysql> SELECT rpd_table_id.TABLE_NAME, rpd_columns.COLUMN_ID, rpd_columns.DICT_SIZE_BYTES
              FROM rpd_table_id, rpd_columns 
              WHERE rpd_table_id.ID = rpd_columns.TABLE_ID AND rpd_columns.DICT_SIZE_BYTES > 0 
              ORDER BY rpd_table_id.TABLE_NAME;
    ------------+-----------+-----------------+
    | TABLE_NAME | COLUMN_ID | DICT_SIZE_BYTES |
    +------------+-----------+-----------------+
    | orders     |         3 |        25165912 |
    +------------+-----------+-----------------+