Patch for Bug#13805127: Stored program cache produces wrong result in same THD.

Background:

  - as described in MySQL Internals Prepared Stored
    (http://forge.mysql.com/wiki/MySQL_Internals_Prepared_Stored),
    the Optimizer sometimes does destructive changes to the parsed
    LEX-object (Item-tree), which makes it impossible to re-use
    that tree for PS/SP re-execution.

  - in order to be able to re-use the Item-tree, the destructive
    changes are remembered and rolled back after the statement execution.

The problem, discovered by this bug, was that the objects representing
GROUP-BY clause did not restored after query execution. So, the GROUP-BY
part of the statement could not be properly re-initialized for re-execution
after destructive changes.

Those objects do not take part in the Item-tree, so they can not be saved
using the approach for Item-tree.

The fix is as follows:

  - introduce a new array in st_select_lex to store the original
    ORDER pointers, representing the GROUP-BY clause;

  - Initialize this array in fix_prepare_information().

  - restore the list of GROUP-BY items in reinit_stmt_before_use().

1 files changed, 175 insertions, 0 deletions

diff --git a/sql/mem_root_array.h b/sql/mem_root_array.h
new file mode 100644
index 00000000000..5ce4dcb584d
--- /dev/null
+++ b/sql/mem_root_array.h
@@ -0,0 +1,175 @@
+/* Copyright (c) 2011, Oracle and/or its affiliates. All rights reserved.
+
+   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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
+
+
+#ifndef MEM_ROOT_ARRAY_INCLUDED
+#define MEM_ROOT_ARRAY_INCLUDED
+
+#include <my_alloc.h>
+
+/**
+   A typesafe replacement for DYNAMIC_ARRAY.
+   We use MEM_ROOT for allocating storage, rather than the C++ heap.
+   The interface is chosen to be similar to std::vector.
+
+   @remark
+   Unlike DYNAMIC_ARRAY, elements are properly copied
+   (rather than memcpy()d) if the underlying array needs to be expanded.
+
+   @remark
+   Depending on has_trivial_destructor, we destroy objects which are
+   removed from the array (including when the array object itself is destroyed).
+
+   @remark
+   Note that MEM_ROOT has no facility for reusing free space,
+   so don't use this if multiple re-expansions are likely to happen.
+
+   @param Element_type The type of the elements of the container.
+          Elements must be copyable.
+   @param has_trivial_destructor If true, we don't destroy elements.
+          We could have used type traits to determine this.
+          __has_trivial_destructor is supported by some (but not all)
+          compilers we use.
+*/
+template<typename Element_type, bool has_trivial_destructor>
+class Mem_root_array
+{
+public:
+  Mem_root_array(MEM_ROOT *root)
+    : m_root(root), m_array(NULL), m_size(0), m_capacity(0)
+  {
+    DBUG_ASSERT(m_root != NULL);
+  }
+
+  ~Mem_root_array()
+  {
+    clear();
+  }
+
+  Element_type &at(size_t n)
+  {
+    DBUG_ASSERT(n < size());
+    return m_array[n];
+  }
+
+  const Element_type &at(size_t n) const
+  {
+    DBUG_ASSERT(n < size());
+    return m_array[n];
+  }
+
+  // Returns a pointer to the first element in the array.
+  Element_type *begin() { return &m_array[0]; }
+
+  // Returns a pointer to the past-the-end element in the array.
+  Element_type *end() { return &m_array[size()]; }
+
+  // Erases all of the elements. 
+  void clear()
+  {
+    if (!empty())
+      chop(0);
+  }
+
+  /*
+    Chops the tail off the array, erasing all tail elements.
+    @param pos Index of first element to erase.
+  */
+  void chop(const size_t pos)
+  {
+    DBUG_ASSERT(pos < m_size);
+    if (!has_trivial_destructor)
+    {
+      for (size_t ix= pos; ix < m_size; ++ix)
+      {
+        Element_type *p= &m_array[ix];
+        p->~Element_type();              // Destroy discarded element.
+      }
+    }
+    m_size= pos;
+  }
+
+  /*
+    Reserves space for array elements.
+    Copies over existing elements, in case we are re-expanding the array.
+
+    @param  n number of elements.
+    @retval true if out-of-memory, false otherwise.
+  */
+  bool reserve(size_t n)
+  {
+    if (n <= m_capacity)
+      return false;
+
+    void *mem= alloc_root(m_root, n * element_size());
+    if (!mem)
+      return true;
+    Element_type *array= static_cast<Element_type*>(mem);
+
+    // Copy all the existing elements into the new array.
+    for (size_t ix= 0; ix < m_size; ++ix)
+    {
+      Element_type *new_p= &array[ix];
+      Element_type *old_p= &m_array[ix];
+      new (new_p) Element_type(*old_p);         // Copy into new location.
+      if (!has_trivial_destructor)
+        old_p->~Element_type();                 // Destroy the old element.
+    }
+
+    // Forget the old array.
+    m_array= array;
+    m_capacity= n;
+    return false;
+  }
+
+  /*
+    Adds a new element at the end of the array, after its current last
+    element. The content of this new element is initialized to a copy of
+    the input argument.
+
+    @param  element Object to copy.
+    @retval true if out-of-memory, false otherwise.
+  */
+  bool push_back(const Element_type &element)
+  {
+    const size_t min_capacity= 20;
+    const size_t expansion_factor= 2;
+    if (0 == m_capacity && reserve(min_capacity))
+      return true;
+    if (m_size == m_capacity && reserve(m_capacity * expansion_factor))
+      return true;
+    Element_type *p= &m_array[m_size++];
+    new (p) Element_type(element);
+    return false;
+  }
+
+  size_t capacity()     const { return m_capacity; }
+  size_t element_size() const { return sizeof(Element_type); }
+  bool   empty()        const { return size() == 0; }
+  size_t size()         const { return m_size; }
+
+private:
+  MEM_ROOT *const m_root;
+  Element_type   *m_array;
+  size_t          m_size;
+  size_t          m_capacity;
+
+  // Not (yet) implemented.
+  Mem_root_array(const Mem_root_array&);
+  Mem_root_array &operator=(const Mem_root_array&);
+};
+
+
+#endif  // MEM_ROOT_ARRAY_INCLUDED