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#ifndef SQL_EXPRESSION_CACHE_INCLUDED
#define SQL_EXPRESSION_CACHE_INCLUDED
#include "sql_select.h"
/**
Interface for expression cache
@note
Parameters of an expression cache interface are set on the creation of the
cache. They are passed when a cache object of the implementation class is
constructed. That's why they are not visible in this interface.
*/
extern ulong subquery_cache_miss, subquery_cache_hit;
class Expression_cache :public Sql_alloc
{
public:
enum result {ERROR, HIT, MISS};
Expression_cache(){};
virtual ~Expression_cache() {};
/**
Shall check the presence of expression value in the cache for a given
set of values of the expression parameters. Return the result of the
expression if it's found in the cache.
*/
virtual result check_value(Item **value)= 0;
/**
Shall put the value of an expression for given set of its parameters
into the expression cache
*/
virtual my_bool put_value(Item *value)= 0;
/**
Print cache parameters
*/
virtual void print(String *str, enum_query_type query_type)= 0;
};
struct st_table_ref;
struct st_join_table;
class Item_field;
/**
Implementation of expression cache over a temporary table
*/
class Expression_cache_tmptable :public Expression_cache
{
public:
Expression_cache_tmptable(THD *thd, List<Item*> &dependants, Item *value);
virtual ~Expression_cache_tmptable();
virtual result check_value(Item **value);
virtual my_bool put_value(Item *value);
void print(String *str, enum_query_type query_type);
private:
void init();
/* tmp table parameters */
TMP_TABLE_PARAM cache_table_param;
/* temporary table to store this cache */
TABLE *cache_table;
/* Thread handle for the temporary table */
THD *table_thd;
/* TABLE_REF for index lookup */
struct st_table_ref ref;
/* Cached result */
Item_field *cached_result;
/* List of references to the parameters of the expression */
List<Item*> *list;
/* List of items */
List<Item> items;
/* Value Item example */
Item *val;
/* Set on if the object has been succesfully initialized with init() */
bool inited;
};
#endif /* SQL_EXPRESSION_CACHE_INCLUDED */
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