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diff --git a/sql/sql_expression_cache.h b/sql/sql_expression_cache.h
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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 */