sql_tmp_table.h File Reference

Temporary table handling functions. More...

#include <sys/types.h>
#include "my_base.h"
#include "my_inttypes.h"
#include "sql/item.h"
#include "sql/temp_table_param.h"

Go to the source code of this file.

Enumerations
enum	enum_internal_tmp_mem_storage_engine { TMP_TABLE_MEMORY , TMP_TABLE_TEMPTABLE }

Functions
TABLE *	create_tmp_table (THD *thd, Temp_table_param *param, const mem_root_deque< Item * > &fields, ORDER *group, bool distinct, bool save_sum_fields, ulonglong select_options, ha_rows rows_limit, const char *table_alias)
bool	open_tmp_table (TABLE *table)
TABLE *	create_tmp_table_from_fields (THD *thd, List< Create_field > &field_list, bool is_virtual=true, ulonglong select_options=0, const char *alias=nullptr)
	Create an, optionally reduced, TABLE object with properly set up Field list from a list of field definitions. More...
bool	create_ondisk_from_heap (THD *thd, TABLE *table, int error, bool insert_last_record, bool ignore_last_dup, bool *is_duplicate)
	If a MEMORY table gets full, create a disk-based table and copy all rows to this. More...
void	close_tmp_table (TABLE *table)
	Close a temporary table at end of preparation or execution. More...
void	free_tmp_table (TABLE *table)
	Free temporary table. More...
TABLE *	create_duplicate_weedout_tmp_table (THD *thd, uint uniq_tuple_length_arg, SJ_TMP_TABLE *sjtbl)
	Create a temporary table to weed out duplicate rowid combinations. More...
bool	setup_tmp_table_handler (THD *thd, TABLE *table, ulonglong select_options, bool force_disk_table=false, bool schema_table=false)
	Helper function to create_tmp_table_* family for setting up table's SE. More...
bool	instantiate_tmp_table (THD *thd, TABLE *table)
	Instantiates temporary table. More...
Field *	create_tmp_field (THD *thd, TABLE *table, Item *item, Item::Type type, Func_ptr_array *copy_func, Field **from_field, Field **default_field, bool group, bool modify_item, bool table_cant_handle_bit_fields, bool make_copy_field)
	Create field for temporary table. More...
Field *	create_tmp_field_from_field (THD *thd, const Field *org_field, const char *name, TABLE *table, Item_field *item)
	Lifecycle management of internal temporary tables. More...
void	get_max_key_and_part_length (uint *max_key_length, uint *max_key_part_length, uint *max_key_parts)
	Get the minimum of max_key_length and max_key_part_length between HEAP engine and internal_tmp_disk_storage_engine. More...
void	init_cache_tmp_engine_properties ()
	Initialize the storage engine properties for the alternative temporary table storage engines. More...
void	encode_innodb_position (uchar *rowid_bytes, uint length, ha_rows row_num)
	Encode an InnoDB PK in 6 bytes, high-byte first; like InnoDB's dict_sys_write_row_id() does. More...
bool	reposition_innodb_cursor (TABLE *table, ha_rows row_num)
	Helper function for create_ondisk_from_heap(). More...

Detailed Description

Temporary table handling functions.

Enumeration Type Documentation

enum_internal_tmp_mem_storage_engine

enum enum_internal_tmp_mem_storage_engine

Enumerator
TMP_TABLE_MEMORY
TMP_TABLE_TEMPTABLE

Function Documentation

close_tmp_table()

void close_tmp_table

(

TABLE *

table

)

Close a temporary table at end of preparation or execution.

Any buffers associated with the table will be released. When tmp_open_count reaches zero, the following will happen:

• If table contents has been created, it will be deleted. When tmp_handler_count reaches zero, the following will happen:
• The storage handler will be deleted and the plugin will be released.

Parameters

table

Table reference

create_duplicate_weedout_tmp_table()

TABLE * create_duplicate_weedout_tmp_table	(	THD *	thd,
		uint	uniq_tuple_length_arg,
		SJ_TMP_TABLE *	sjtbl
	)

Create a temporary table to weed out duplicate rowid combinations.

Parameters

thd	Thread handle
uniq_tuple_length_arg	Length of the table's column
sjtbl	Update sjtbl->[start_]recinfo values which will be needed if we'll need to convert the created temptable from HEAP to MyISAM/Maria.

create_duplicate_weedout_tmp_table()

Create a temporary table to weed out duplicate rowid combinations. The table has a single column that is a concatenation of all rowids in the combination.

Depending on the needed length, there are two cases:

1. When the length of the column < max_key_length:

   CREATE TABLE tmp (col VARBINARY(n) NOT NULL, UNIQUE KEY(col));

2. Otherwise (not a valid SQL syntax but internally supported):

   CREATE TABLE tmp (col VARBINARY NOT NULL, UNIQUE CONSTRAINT(col));

The code in this function was produced by extraction of relevant parts from create_tmp_table().

Returns

created table NULL on error

create_ondisk_from_heap()

bool create_ondisk_from_heap	(	THD *	thd,
		TABLE *	wtable,
		int	error,
		bool	insert_last_record,
		bool	ignore_last_dup,
		bool *	is_duplicate
	)

If a MEMORY table gets full, create a disk-based table and copy all rows to this.

Parameters

[in]	thd	THD reference
[in]	wtable	Table reference being written to
[in]	error	Reason why inserting into MEMORY table failed.
[in]	insert_last_record	If true, the last record(table->record[0]) is inserted into the newly created table after copying all the records from the temp table. If false, the last record is not inserted and the parameters ignore_last_dup, is_duplicate are ignored.
[in]	ignore_last_dup	If true, ignore duplicate key error for last inserted key (see detailed description below).
[out]	is_duplicate	If non-NULL and ignore_last_dup is true, return true if last key was a duplicate, and false otherwise.

Function can be called with any error code, but only HA_ERR_RECORD_FILE_FULL will be handled, all other errors cause a fatal error to be thrown. The function creates a disk-based temporary table, copies all records from the MEMORY table into this new table, deletes the old table and switches to use the new table within the table handle. The function uses table->record[1] as a temporary buffer while copying.

If the parameter insert_last_record is true, this function assumes that table->record[0] contains the row that caused the error when inserting into the MEMORY table (the "last row"). After all existing rows have been copied to the new table,the last row is attempted to be inserted as well. If ignore_last_dup is true, this row can be a duplicate of an existing row without throwing an error. If is_duplicate is non-NULL, an indication of whether the last row was a duplicate is returned.

If the parameter insert_last_record is false, this function makes no assumptions on the operation and will not try an insert of the last record(table->record[0]). The caller is expected to handle the operation after moving to disk.

Note

that any index/scan access initialized on the MEMORY 'wtable' is not replicated to the on-disk table - it's the caller's responsibility. However, access initialized on other TABLEs, is replicated.

If 'wtable' has other TABLE clones (example: a multi-referenced or a recursive CTE), we convert all clones; if an error happens during conversion of clone B after successfully converting clone A, clone A and B will exit from the function with a TABLE_SHARE corresponding to the pre-conversion table ("old" TABLE_SHARE). So A will be inconsistent (for example s->db_type() will say "MEMORY" while A->file will be a disk-based engine). However, as all callers bail out, it is reasonable to think that they won't be using the TABLE_SHARE except in free_tmp_table(); and free_tmp_table() only uses properties of TABLE_SHARE which are common to the old and new object (reference counts, MEM_ROOT), so that should work. Solutions to fix this cleanly:

• allocate new TABLE_SHARE on heap instead of on stack, to be able to exit with two TABLE_SHAREs (drawback: more heap memory consumption, and need to verify all exit paths are safe),
• close all TABLEs if error (but then callers and cleanup code may be surprised to find already-closed tables so they would need fixing). To lower the risk of error between A and B: we expect most errors will happen when copying rows (e.g. read or write errors); so we convert 'wtable' (which does the row copying) first; if it fails, the A-B situation is avoided and we can properly exit with the old TABLE_SHARE.

Returns

true if error.

create_tmp_field()

Field * create_tmp_field	(	THD *	thd,
		TABLE *	table,
		Item *	item,
		Item::Type	type,
		Func_ptr_array *	copy_func,
		Field **	from_field,
		Field **	default_field,
		bool	group,
		bool	modify_item,
		bool	table_cant_handle_bit_fields,
		bool	make_copy_field
	)

Create field for temporary table.

Parameters

thd	Thread handler
table	Temporary table
item	Item to create a field for
type	Type of item (normally item->type)
copy_func	If set and item is a function, store copy of item in this array
from_field	if field will be created using other field as example, pointer example field will be written here
default_field	If field has a default value field, store it here
group	1 if we are going to do a relative group by on result
modify_item	1 if item->result_field should point to new item. This is relevant for how fill_record() is going to work: If modify_item is 1 then fill_record() will update the record in the original table. If modify_item is 0 then fill_record() will update the temporary table
table_cant_handle_bit_fields	if table can't handle bit-fields and bit-fields shall be converted to long

See also

Temp_table_param::bit_fields_as_long

Parameters

make_copy_field

if true, a pointer of the result field should be stored in from_field, otherwise the item should be wrapped in Func_ptr and stored in copy_func

Return values

NULL	On error.
new_created	field

create_tmp_field_from_field()

Field * create_tmp_field_from_field	(	THD *	thd,
		const Field *	org_field,
		const char *	name,
		TABLE *	table,
		Item_field *	item
	)

Lifecycle management of internal temporary tables.

An internal temporary table is represented by a TABLE_SHARE object.

The interface to an internal temporary table is through one or more TABLE objects, of which at most one TABLE object is a writer object, the remaining TABLE objects are reader objects. Each TABLE object points to the TABLE_SHARE. TABLE_SHARE::ref_count counts the number of TABLE objects that points to it.

The TABLE, TABLE_SHARE and associated objects (e.g Field objects) are created in a dedicated mem_root. This mem_root is deleted when the TABLE_SHARE object is deleted.

Initially, an internal temporary table is created with one TABLE_SHARE object and one TABLE object. The table is created with no file handler (storage engine) and in the "deleted" state. Later, more TABLE objects may be created against the table, and TABLE_SHARE::ref_count is increased.

An internal temporary table may be instantiated and used multiple times, typically once per execution of a statement.

To instantiate a table, call instantiate_tmp_table(). This function will first assign and lock a storage engine using setup_tmp_table_handler(). The locked engine is assigned to TABLE_SHARE::db_plugin and the file handler is assigned to TABLE::file. After this, calling TABLE::has_storage_handler() reports true.

After this, the table contents is created by calling TABLE::file->create() and the table is opened by calling open_tmp_table(), which itself calls TABLE::file->ha_open(), and sets the TABLE::created flag.

Thus, opening a temporary table is a two-stage operation:

1. assign and lock a storage engine, and
2. create the table contents.

Since a temporary table may be in any of the two stages, we use two counter members in the TABLE_SHARE to count the number of TABLEs in each of the stages: tmp_handler_count and tmp_open_count. tmp_handler_count is incremented in setup_tmp_table_handler(). tmp_open_count is incremented in open_tmp_table().

To open an already instantiated table, assign a storage handler by calling setup_tmp_table_handler(), then call open_tmp_table() which will again increment TABLE_SHARE::tmp_open_count and set TABLE::created.

Insert, update, delete and read rows using the active TABLE handlers.

After use, close all active TABLE handlers by calling close_tmp_table(). For simplicity, we may also call close_tmp_table() on a non-active TABLE, as it will check whether a storage handler has been assigned.

If the table is created, TABLE_SHARE::tmp_open_count is decremented. If there are no remaining active TABLE objects, delete the table contents by calling TABLE::file->ha_drop_table(), otherwise close it by calling TABLE::file->ha_close(). Set status of the TABLE to deleted and delete the storage handler. If there are no remaining active tables and the storage engine is still locked, unlock the plugin and disassociate it from the TABLE_SHARE object, and decrement TABLE_SHARE::tmp_handler_count.

After the final instantiation of an internal temporary table, call free_tmp_table() for all associated TABLE objects.

free_tmp_table() can only be called on a non-instantiated temporary table (but handlers may be assigned for other TABLE objects to the same table).. It will decrement TABLE_SHARE::ref_count and the final call will also remove the temporary table's mem_root object. Create field for temporary table from given field.

Parameters

thd	Thread handler
org_field	Field from which new field will be created
name	New field name
table	Temporary table
item	If item != NULL then fill_record() will update the record in the original table. If item == NULL then fill_record() will update the temporary table

Return values

NULL	on error
new_created	field

create_tmp_table()

TABLE * create_tmp_table	(	THD *	thd,
		Temp_table_param *	param,
		const mem_root_deque< Item * > &	fields,
		ORDER *	group,
		bool	distinct,
		bool	save_sum_fields,
		ulonglong	select_options,
		ha_rows	rows_limit,
		const char *	table_alias
	)

When true, enforces unique constraint (by adding a hidden hash field and creating a key over this field) when: (1) unique key is too long, or (2) number of key parts in distinct key is too big, or (3) the caller has requested it. (4) we have INTERSECT or EXCEPT, i.e. not UNION.

create_tmp_table_from_fields()

TABLE * create_tmp_table_from_fields	(	THD *	thd,
		List< Create_field > &	field_list,
		bool	is_virtual,
		ulonglong	select_options,
		const char *	alias
	)

Create an, optionally reduced, TABLE object with properly set up Field list from a list of field definitions.

When is_virtual arg is true: The created table doesn't have a table handler associated with it, has no keys, no group/distinct, no copy_funcs array. The sole purpose of this TABLE object is to use the power of Field class to read/write data to/from table->record[0]. Then one can store the record in any container (RB tree, hash, etc). The table is created in THD mem_root, so are the table's fields. Consequently, if you don't BLOB fields, you don't need to free it. When is_virtual is false: This function creates a normal tmp table out of fields' definitions, rather than from lst of items. This is the main difference with create_tmp_table. Also the table created here doesn't do grouping, doesn't have indexes and copy_funcs/fields. The purpose is to be able to create result table for table functions out of fields' definitions without need in intermediate list of items.

Parameters

thd	connection handle
field_list	list of column definitions
is_virtual	if true, then it's effectively only a record buffer with wrapper, used e.g to store vars in SP if false, then a normal table, which can hold records, is created
select_options	options for non-virtual tmp table
alias	table's alias

Returns

0 if out of memory, TABLE object in case of success

encode_innodb_position()

void encode_innodb_position	(	uchar *	rowid_bytes,
		uint	length,
		ha_rows	row_num
	)

Encode an InnoDB PK in 6 bytes, high-byte first; like InnoDB's dict_sys_write_row_id() does.

Parameters

rowid_bytes	where to store the result
length	how many available bytes in rowid_bytes
row_num	PK to encode

free_tmp_table()

void free_tmp_table

(

TABLE *

table

)

Free temporary table.

When ref_count reaches zero, the table's mem_root allocator is deleted.

Parameters

table

Table reference

get_max_key_and_part_length()

void get_max_key_and_part_length	(	uint *	max_key_length,
		uint *	max_key_part_length,
		uint *	max_key_parts
	)

Get the minimum of max_key_length and max_key_part_length between HEAP engine and internal_tmp_disk_storage_engine.

Get the minimum of max_key_length and max_key_part_length between HEAP engine and internal_tmp_disk_storage_engine.

The minimum is between HEAP engine and internal_tmp_disk_storage_engine.

Parameters

[out]	max_key_length	Minimum of max_key_length
[out]	max_key_part_length	Minimum of max_key_part_length
[out]	max_key_parts	Minimum of max_key_parts

init_cache_tmp_engine_properties()

void init_cache_tmp_engine_properties

(

)

Initialize the storage engine properties for the alternative temporary table storage engines.

instantiate_tmp_table()

bool instantiate_tmp_table	(	THD *	thd,
		TABLE *	table
	)

Instantiates temporary table.

Parameters

thd	Thread handler
table	Table object that describes the table to be instantiated Creates temporary table and opens it.

Returns

false if success, true if error

open_tmp_table()

bool open_tmp_table

(

TABLE *

table

)

reposition_innodb_cursor()

bool reposition_innodb_cursor	(	TABLE *	table,
		ha_rows	row_num
	)

Helper function for create_ondisk_from_heap().

Our InnoDB on-disk intrinsic table uses an autogenerated auto-incrementing primary key:

• first inserted row has pk=1 (see dict_table_get_next_table_sess_row_id()), second has pk=2, etc
• ha_rnd_next uses a PK index scan so returns rows in PK order
• position() returns the PK
• ha_rnd_pos() takes the PK in input.

Parameters

table	table read by cursor
row_num	function should position on the row_num'th row in insertion order.

setup_tmp_table_handler()

bool setup_tmp_table_handler	(	THD *	thd,
		TABLE *	table,
		ulonglong	select_options,
		bool	force_disk_table,
		bool	schema_table
	)

Helper function to create_tmp_table_* family for setting up table's SE.

Parameters

thd	Thread handler
table	table to allocate SE for
select_options	Options that may control storage engine selection
force_disk_table	true <=> Use InnoDB
schema_table	whether the table is a schema table

Returns

false if success, true if error

Note

In a prepared statement, both preparation and execution may use this function, for a same TABLE. Execution always uses force_disk_table=schema_table=false; this may be inconsistent with what was used at preparation, but it's ok in fact:

• force_disk_table=true is for semijoin duplicate elimination table, which is execution-only
• schema_table=true is for schema tables, and they're re-created at each execution.