[Compressed columns with dictionaries] 5.7 supports JSON column compression

[Laurynas Biveinis]

[In:/doc/percona-server/LATEST/flexibility/compressed_columns.html]

In 5.7, JSON is one of the supported data types for compressed columns with dictionaries, this must be stated.

[Yura Sorokin (yura-sorokin)]

Please, also add that 5.7 generated columns (both virtual and stored) can refer to compressed columns.

Moreover, we added syntax extension for stored generated columns, which allows to specify COLUMN_FORMAT COMPRESSED for them.

For instance,

CREATE TABLE t1(
  id INT,
  a BLOB,
  g BLOB GENERATED ALWAYS AS (a) STORED COLUMN_FORMAT COMPRESSED WITH COMPRESSION_DICTIONARY numbers
) ENGINE=InnoDB;

[Alexander Rubin (alikrubin75)]

Changing a column from uncompressed to compressed for JSON crashes the server:

mysql> alter table tb_name modify json_variables JSON COLUMN_FORMAT compressed;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0

2017-07-13T15:21:22.114757Z 3 [ERROR] [FATAL] InnoDB: unsupported compressed BLOB header format

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PS-1058