Hi Jan!
We are in the process of re-designing the current on-line alter table
interface (which currently
only supports add/drop index). The old interface is based on handlers
having "capability"
flags (handlerton::alter_table_flags) and the MySQL server orchestrates
the steps needed for
different alter table operations. After discussions this approach has
been decided to
be too complex since different storage engines need to do various
operations in
different ways. Also adding flags and new handler calls for each
possible change will
make the handler interface huge.
The current plan is to add more general calls (note that the interface
is still under design
and might change, but you should get the idea):
One call for asking the handler if it can do the alteration on-line:
int handler::check_if_supported_alter(TABLE *altered_table,
HA_CREATE_INFO *create_info,
HA_ALTER_FLAGS alter_flags,
uint table_changes);
where HA_ALTER_FLAGS is defined by:
#define HA_ADD_INDEX (1L << 0)
#define HA_DROP_INDEX (1L << 1)
#define HA_ALTER_INDEX (1L << 2)
#define HA_RENAME_INDEX (1L << 3)
#define HA_ADD_UNIQUE_INDEX (1L << 4)
#define HA_DROP_UNIQUE_INDEX (1L << 5)
#define HA_ALTER_UNIQUE_INDEX (1L << 6)
#define HA_RENAME_UNIQUE_INDEX (1L << 7)
#define HA_ADD_PK_INDEX (1L << 8)
#define HA_DROP_PK_INDEX (1L << 9)
#define HA_ALTER_PK_INDEX (1L << 10)
#define HA_ADD_COLUMN (1L << 11)
#define HA_DROP_COLUMN (1L << 12)
#define HA_ALTER_COLUMN_NAME (1L << 13)
#define HA_ALTER_COLUMN_TYPE (1L << 14)
#define HA_ALTER_COLUMN_ORDER (1L << 15)
#define HA_ADD_FOREIGN_KEY (1L << 16)
#define HA_DROP_FOREIGN_KEY (1L << 17)
#define HA_ADD_CONSTRAINT (1L << 18)
#define HA_ADD_PARTITION (1L << 19)
#define HA_DROP_PARTITION (1L << 20)
#define HA_COALESCE_PARTITION (1L << 21)
#define HA_REORGANIZE_PARTITION (1L << 22)
#define HA_CHANGE_CHARACTER_SET (1L << 23)
#define HA_SET_DEFAULT_CHARACTER_SET (1L << 24)
#define HA_RENAME_TABLE (1L << 25)
Two calls are currently planned for executing the actual alteration:
int handler::prepare_alter_table(TABLE *altered_table,
HA_CREATE_INFO *create_info,
HA_ALTER_FLAGS alter_flags);
int handler::alter_table(TABLE *altered_table,
HA_CREATE_INFO *create_info,
HA_ALTER_FLAGS alter_flags);
The only flag I see missing here would be for setting/changing column
defaults, I will consider
adding some flag(s) for that. The flags are supposed to hint what
changes are made to the table,
and the 'altered_table' argument will allow the handler to check exactly
what has changed.
Please feel free to comment if you see something missing in the current
proposal.
BR
-- Martin
Jan Lindström wrote:
> Hi,
>
> I propose few additional functions to MySQL storage engine handler
> interface:
>
> ::add_foreign_keys(THD* thd, TABLE *table_arg, foreign_key* fk_key, uint
> n_fkeys);
> Assuming that HA_CAN_ADD_FOREIGN_KEYS is set this
> function is used for implementing alter table add
> foreign key ...
>
> ::drop_foreign_keys(THD* thd, TABLE *table_arg, char* fk_names, uint
> n_fkeys);
>
> Assuming that HA_CAN_DROP_FOREIGN_KEYS is set
> this function is used to implement alter table drop foreign
> key...
>
> ::set_column_defaults(THD* thd, TABLE *table_arg, char* field_names,
> mysql_byte* default_values, uint n_defvalues);
>
> Assuming that HA_CAN_SET_DEFAUL_CASCADE is set this function
> is used to modify column default value in alter table modify
> column a set default ...
>
> Note that this would require that storage engine can in ::create
> determine default value for the column (e.g.
> Field->get_default_value())
>
> ::add_columns(THD* thd, TABLE *table_arg, Field* fields, uint n_fields);
>
> Assuming that HA_CAN_ADD_COLUMNS is set this function is used
> to implement alter table add column ...
>
> ::drop_columns(THD* thd, TABLE *table_arg, char* field_names, uint
> n_fields);
> Assuming that HA_CAN_DROP_COLUMNS is set this function is used
> to implement alter table drop column ...
>
> R: Jan Lindström
> Solid Information Technology Ltd
>
>
>
--
Martin Sköld, Ph.D
Software Engineer
MySQL AB, www.mysql.com
Office: +46 (0)730 31 26 21
