Add TABLE_SHARE::foreign_keys and TABLE_SHARE::referenced_keys as pointers to List<FOREIGN_KEY_INFO>.
Remove handler foreign key interface: get_foreign_key_list(), get_parent_foreign_key_list(), referenced_by_foreign_key().
Remove cached TABLE_SHARE objects of referenced tables when foreign table is dropped, renamed or altered (add foreign key, rename column of foreign key).
Remove cached TABLE_SHARE objects of foreign tables when referenced table is renamed or altered (rename column of referenced key).
Debug build: check consistency between opened foreign and referenced tables on table flush.
1. Introduce Foreign_key_io class which creates/parses binary stream containing foreign key structures. Referenced tables store there only hints about foreign tables (their db and name), they restore full info from the corresponding tables.
Foreign_key_io is stored under new EXTRA2_FOREIGN_KEY_INFO field in extra2 section of FRM file.
2. Modify mysql_prepare_create_table() to generate names for foreign keys. Until InnoDB storage of foreign keys is removed, FK names must be unique across the database: the FK name must be based on table name.
3. Keep stored data in sync on DDL changes. Referenced tables update their foreign hints after following operations on foreign tables:
ADD FOREIGN KEY
DROP FOREIGN KEY
Foreign tables update their foreign info after following operations on referenced tables:
4. To achieve 3. there must be ability to rewrite extra2 section of FRM file without full reparse. FRM binary is built from primary structures like HA_CREATE_INFO and cannot be built from TABLE_SHARE.
Use shadow write and rename like fast_alter_partition_table() does.
mysql_prepare_create_table() does data validation and such utilities as automatic name generation. But it does that only for indexes and ignores Foreign_key objects. Now as Foreign_key data needs to be stored in FRM files as well this processing must be done for them like for any other Key objects.
Replace Key::FOREIGN_KEY type with Key::foreign flag of type Key::MULTIPLE and Key::generated set to true. Construct one object with Key::foreign == true instead of two objects of type Key::FOREIGN_KEY and Key::MULTIPLE.