Re: Adding new funtions to handler interface

[Jan Lindström]

Hi,

This looks very promising. Column default values are needed for
referential action set default in foreign keys. Any idea of MySQL
version where this new alter table interface is planned ?

R: Jan

> 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
> >
> >
> >   
> 
>