MDEV-11371 - column compression

Storage engine independent support for column compression.

TINYBLOB, BLOB, MEDIUMBLOB, LONGBLOB, TINYTEXT, TEXT, MEDIUMTEXT, LONGTEXT,
VARCHAR and VARBINARY columns can be compressed.

New COMPRESSED column attribute added:
COMPRESSED[=<compression_method>]

System variables added:
column_compression_threshold
column_compression_zlib_level
column_compression_zlib_strategy
column_compression_zlib_wrap

Status variables added:
Column_compressions
Column_decompressions

Limitations:
- the only supported method currently is zlib
- CSV storage engine stores data uncompressed on-disk even if COMPRESSED
  attribute is present
- it is not possible to create indexes over compressed columns.

sql/sql_table.cc

@@ -3690,6 +3690,14 @@ mysql_prepare_create_table(THD *thd, HA_CREATE_INFO *create_info,
 	  DBUG_RETURN(TRUE);
 	}
       }
+
+      if (sql_field->compression_method())
+      {
+        my_error(ER_COMPRESSED_COLUMN_USED_AS_KEY, MYF(0),
+                 column->field_name.str);
+        DBUG_RETURN(TRUE);
+      }
+
       cols2.rewind();
       if (key->type == Key::FULLTEXT)
       {