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+/*
+ Copyright (c) 2010, 2011, Monty Program Ab
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; version 2 of the License.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program; if not, write to the Free Software
+ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA */
+
+#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()= default;
+ virtual ~Expression_cache() = default;
+ /**
+ 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;
+
+ /**
+ Is this cache initialized
+ */
+ virtual bool is_inited()= 0;
+ /**
+ Initialize this cache
+ */
+ virtual void init()= 0;
+
+ /**
+ Save this object's statistics into Expression_cache_tracker object
+ */
+ virtual void update_tracker()= 0;
+};
+
+struct st_table_ref;
+struct st_join_table;
+class Item_field;
+
+
+class Expression_cache_tracker :public Sql_alloc
+{
+public:
+ enum expr_cache_state {UNINITED, STOPPED, OK};
+ Expression_cache_tracker(Expression_cache *c) :
+ cache(c), hit(0), miss(0), state(UNINITED)
+ {}
+
+private:
+ // This can be NULL if the cache is already deleted
+ Expression_cache *cache;
+
+public:
+ ulong hit, miss;
+ enum expr_cache_state state;
+
+ static const char* state_str[3];
+ void set(ulong h, ulong m, enum expr_cache_state s)
+ {hit= h; miss= m; state= s;}
+
+ void detach_from_cache() { cache= NULL; }
+ void fetch_current_stats()
+ {
+ if (cache)
+ cache->update_tracker();
+ }
+};
+
+
+/**
+ 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);
+ bool is_inited() { return inited; };
+ void init();
+
+ void set_tracker(Expression_cache_tracker *st)
+ {
+ tracker= st;
+ update_tracker();
+ }
+ virtual void update_tracker()
+ {
+ if (tracker)
+ {
+ tracker->set(hit, miss, (inited ? (cache_table ?
+ Expression_cache_tracker::OK :
+ Expression_cache_tracker::STOPPED) :
+ Expression_cache_tracker::UNINITED));
+ }
+ }
+
+private:
+ void disable_cache();
+
+ /* 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;
+ /* EXPALIN/ANALYZE statistics */
+ Expression_cache_tracker *tracker;
+ /* TABLE_REF for index lookup */
+ struct st_table_ref ref;
+ /* Cached result */
+ Item_field *cached_result;
+ /* List of parameter items */
+ List<Item> &items;
+ /* Value Item example */
+ Item *val;
+ /* hit/miss counters */
+ ulong hit, miss;
+ /* Set on if the object has been successfully initialized with init() */
+ bool inited;
+};
+
+#endif /* SQL_EXPRESSION_CACHE_INCLUDED */