1. Roland Bouman
http://rpbouman.blogspot.com/
1
Writing MySQL 5.1 Information
Schema Plugins

2. Roland Bouman
http://rpbouman.blogspot.com/
2
Tasks Before Implementing
Information Schema Plugins
● Standard headers
– <stdlib.h>, <ctype.h>
● Non-specific MySQL headers:
– <mysql_version.h>, <mysql/plugin.h>
● Extra headers for Information Schema plug-ins
– <mysql_priv.h>
– <my_global.h>
– <my_dir.h>

3. Roland Bouman
http://rpbouman.blogspot.com/
3
Implementing Information
Schema Plug-ins
● Setup the column layout
– Defines the column names and data types
● Implement a fill function
– Is called to fill the (in-memory) table
● Hook up table object with colum layout and fill
function
– Plug-in initialization function

4. Roland Bouman
http://rpbouman.blogspot.com/
4
Information Schema Plug-ins:
Column Layout
● Array of ST_FIELD_INFO
– typedef struct st_field_info
– Defined in sql/table.h
typedef struct st_field_info
{
const char* field_name;
uint field_length;
enum enum_field_types field_type;
int value;
uint field_flags;
const char* old_name;
uint open_method;
} ST_FIELD_INFO;

5. Roland Bouman
http://rpbouman.blogspot.com/
5
ST_FIELD_INFO members (1/2)
● field_name: Column name
● field_length:
– String type columns: #characters
– Non-string types: 'display length'
● field_type: type constant
– enum_field_types (mysql_com.h)
● field_flags:
– MY_I_S_MAYBE_NULL
– MY_I_S_UNSIGNED

6. Roland Bouman
http://rpbouman.blogspot.com/
6
ST_FIELD_INFO members (2/2)
● open_method: (sql/table.h)
– SKIP_OPEN_TABLE
– OPEN_FRM_ONLY
– OPEN_FULL_TABLE
● old_name: Column name for SHOW command
● value: ??

7. Roland Bouman
http://rpbouman.blogspot.com/
7
Information Schema Plug-ins:
Column Layout Example
● information_schema.SCHEMATA
ST_FIELD_INFO schema_fields_info[]=
{
{"CATALOG_NAME", FN_REFLEN, MYSQL_TYPE_STRING,
0, 1, 0, SKIP_OPEN_TABLE},
{"SCHEMA_NAME", NAME_CHAR_LEN, MYSQL_TYPE_STRING,
0, 0, "Database", SKIP_OPEN_TABLE},
{"DEFAULT_CHARACTER_SET_NAME", MY_CS_NAME_SIZE, MYSQL_TYPE_STRING,
0, 0, 0, SKIP_OPEN_TABLE},
{"DEFAULT_COLLATION_NAME", MY_CS_NAME_SIZE, MYSQL_TYPE_STRING,
0, 0, 0, SKIP_OPEN_TABLE},
{"SQL_PATH", FN_REFLEN, MYSQL_TYPE_STRING,
0, 1, 0, SKIP_OPEN_TABLE},
{0, 0, MYSQL_TYPE_STRING, 0, 0, 0, SKIP_OPEN_TABLE}
}

8. Roland Bouman
http://rpbouman.blogspot.com/
8
Information Schema Plug-ins:
Fill Function (1/4)
● fill_table(
THD *thd,
TABLE_LIST *tables,
COND *cond
)
● THD: thread descriptor (sql/sql_class.h)
● TABLE_LIST: (sql/sql_table.h)
– List of struct st_table (a.k.a. TABLE)
● COND: Condition.

9. Roland Bouman
http://rpbouman.blogspot.com/
9
Information Schema Plug-ins:
Fill Function (2/4)
● Grab first table from the list:
TABLE *table= (TABLE *)tables->table;
● Store data in fields:
table->field[i]->store(...);
● Store row in table
schema_table_store_record(thd, table);

10. Roland Bouman
http://rpbouman.blogspot.com/
10
Information Schema Plug-ins:
Fill Function (3/4)
● schema_table_store_record(
THD *thd
, TABLE *table
)
● Forward declaration in mysql_priv.h
● Defined in sql/sql_show.cc

11. Roland Bouman
http://rpbouman.blogspot.com/
11
Information Schema Plug-ins:
Fill Function (4/4)
int myplugin_fill_table(
THD *thd, TABLE_LIST *tables, COND *cond
){
int status;
CHARSET_INFO *scs= system_charset_info;
TABLE *table= (TABLE *)tables->table;
for ( ... ) { //
table->field[0]->store( ... );
...
table->field[X]->store( ... );
status= schema_table_store_record(
thd, table
);
}
return status;
}

12. Roland Bouman
http://rpbouman.blogspot.com/
12
Information Schema Plug-ins:
Hookup Column Layout and Filler
● plugin_init
static int myplugin_init(void *p)
{
ST_SCHEMA_TABLE *schema= (ST_SCHEMA_TABLE *)p;
schema->fields_info= myplugin_field_info;
schema->fill_table= myplugin_fill_table;
return 0;
}

13. Roland Bouman
http://rpbouman.blogspot.com/
13
Information Schema Plug-ins:
ST_SCHEMA_TABLE
● ST_SCHEMA_TABLE a.k.a st_schema_table
typedef struct st_schema_table
{
const char* table_name;
ST_FIELD_INFO *fields_info;
TABLE *(*create_table)(THD *thd, TABLE_LIST *table_list);
int (*fill_table) (
THD *thd, TABLE_LIST *tables, COND *cond);
int (*old_format) (
THD *thd, struct st_schema_table *schema_table);
int (*process_table) (
THD *thd, TABLE_LIST *tables,TABLE *table,
bool res, LEX_STRING *db_name, LEX_STRING *table_name);
int idx_field1, idx_field2;
bool hidden;
uint i_s_requested_object;
} ST_SCHEMA_TABLE;

14. Roland Bouman
http://rpbouman.blogspot.com/
14
Information Schema Plug-ins:
Hookup Column Layout and Filler
● plugin_init
static int myplugin_init(void *p)
{
ST_SCHEMA_TABLE *schema= (ST_SCHEMA_TABLE *)p;
schema->fields_info= myplugin_field_info;
schema->fill_table= myplugin_fill_table;
return 0;
}

15. Roland Bouman
http://rpbouman.blogspot.com/
15
Information Schema Plug-ins:
Hookup Column Layout and Filler
● plugin_init
static int myplugin_init(void *p)
{
ST_SCHEMA_TABLE *schema= (ST_SCHEMA_TABLE *)p;
schema->fields_info= myplugin_field_info;
schema->fill_table= myplugin_fill_table;
return 0;
}

16. Roland Bouman
http://rpbouman.blogspot.com/
16
Information Schema Plug-ins:
Hookup Column Layout and Filler
● plugin_init
static int myplugin_init(void *p)
{
ST_SCHEMA_TABLE *schema= (ST_SCHEMA_TABLE *)p;
schema->fields_info= myplugin_field_info;
schema->fill_table= myplugin_fill_table;
return 0;
}