Make cursor implementation uniform

Cursors now report their current row number as the boundary of the
partition. This is used by Frame_scan_cursor to compute aggregate
functions that do not support removal.

sql/sql_window.cc

@@ -4,6 +4,7 @@
 #include "filesort.h"
 #include "sql_base.h"
 #include "sql_window.h"
+#include "my_dbug.h"
 
 
 bool
@@ -549,29 +550,44 @@ public:
     ref_length= info->ref_length;
   }
 
-  virtual int get_next()
+  virtual int next()
   {
-    /* Allow multiple get_next() calls in EOF state*/
+    /* Allow multiple next() calls in EOF state. */
     if (cache_pos == cache_end)
       return -1;
+
     cache_pos+= ref_length;
+    DBUG_ASSERT(cache_pos <= cache_end);
+
     return 0;
   }
 
-  ha_rows get_rownum()
+  virtual int prev()
+  {
+    /* Allow multiple prev() calls when positioned at the start. */
+    if (cache_pos == cache_start)
+      return -1;
+    cache_pos-= ref_length;
+    DBUG_ASSERT(cache_pos >= cache_start);
+
+    return 0;
+  }
+
+  ha_rows get_rownum() const
   {
     return (cache_pos - cache_start) / ref_length;
   }
 
   void move_to(ha_rows row_number)
   {
-    cache_pos= cache_start + row_number * ref_length;
+    cache_pos= MY_MIN(cache_end, cache_start + row_number * ref_length);
+    DBUG_ASSERT(cache_pos <= cache_end);
   }
 
 protected:
   bool at_eof() { return (cache_pos == cache_end); }
 
-  uchar *get_last_rowid()
+  uchar *get_prev_rowid()
   {
     if (cache_pos == cache_start)
       return NULL;
@@ -601,30 +617,25 @@ public:
   void init(READ_RECORD *info)
   {
     Rowid_seq_cursor::init(info);
-    read_record= info;
+    table= info->table;
+    record= info->record;
   }
 
-  virtual int get_next()
+  virtual int fetch()
   {
     if (at_eof())
       return -1;
 
     uchar* curr_rowid= get_curr_rowid();
-    int res= Rowid_seq_cursor::get_next();
-    if (!res)
-    {
-      res= read_record->table->file->ha_rnd_pos(read_record->record,
-                                                curr_rowid);
-    }
-    return res;
+    return table->file->ha_rnd_pos(record, curr_rowid);
   }
 
-  bool restore_last_row()
+  bool fetch_prev_row()
   {
     uchar *p;
-    if ((p= get_last_rowid()))
+    if ((p= get_prev_rowid()))
     {
-      int rc= read_record->table->file->ha_rnd_pos(read_record->record, p);
+      int rc= table->file->ha_rnd_pos(record, p);
       if (!rc)
         return true; // restored ok
     }
@@ -632,11 +643,10 @@ public:
   }
 
 private:
-  /*
-    Note: we don't own *read_record, somebody else is using it.
-    We only look at the constant part of it, e.g. table, record buffer, etc.
-  */
-  READ_RECORD *read_record;
+  /* The table that is acccesed by this cursor. */
+  TABLE *table;
+  /* Buffer where to store the table's record data. */
+  uchar *record;
 
   // TODO(spetrunia): should move_to() also read row here?
 };
@@ -645,6 +655,8 @@ private:
 /*
   A cursor which only moves within a partition. The scan stops at the partition
   end, and it needs an explicit command to move to the next partition.
+
+  This cursor can not move backwards.
 */
 
 class Partition_read_cursor : public Table_read_cursor
@@ -669,39 +681,36 @@ public:
   void on_next_partition(ha_rows rownum)
   {
     /* Remember the sort key value from the new partition */
+    move_to(rownum);
     bound_tracker.check_if_next_group();
     end_of_partition= false;
-  }
 
-  /*
-    Moves to a new row. The row is assumed to be within the current partition.
-  */
-  void move_to(ha_rows rownum) { Table_read_cursor::move_to(rownum); }
+  }
 
   /*
     This returns -1 when end of partition was reached.
   */
-  int get_next()
+  int next()
   {
     int res;
     if (end_of_partition)
       return -1;
-    if ((res= Table_read_cursor::get_next()))
+
+    if ((res= Table_read_cursor::next()) ||
+        (res= fetch()))
       return res;
 
     if (bound_tracker.compare_with_cache())
     {
+      /* This row is part of a new partition, don't move
+         forward any more untill we get informed of a new partition. */
+      Table_read_cursor::prev();
       end_of_partition= true;
       return -1;
     }
     return 0;
   }
 
-  bool restore_last_row()
-  {
-    return Table_read_cursor::restore_last_row();
-  }
-
 private:
   Group_bound_tracker bound_tracker;
   bool end_of_partition;
@@ -783,6 +792,8 @@ public:
   virtual void pre_next_row() {};
   virtual void next_row()=0;
 
+  virtual bool is_outside_computation_bounds() const { return false; };
+
   virtual ~Frame_cursor() {}
 
   /*
@@ -796,7 +807,7 @@ public:
   }
 
   /* Retrieves the row number that this cursor currently points at. */
-  virtual ha_rows get_curr_rownum()= 0;
+  virtual ha_rows get_curr_rownum() const= 0;
 
 protected:
   inline void add_value_to_items()
@@ -962,7 +973,6 @@ public:
 
   void next_partition(ha_rows rownum)
   {
-    cursor.move_to(rownum);
     walk_till_non_peer();
   }
 
@@ -982,26 +992,39 @@ public:
         (prev_row + n) >= R
       We need to check about the current row.
     */
-    if (cursor.restore_last_row())
-    {
-      if (order_direction * range_expr->cmp_read_only() <= 0)
-        return;
-      remove_value_from_items();
-    }
     walk_till_non_peer();
   }
 
-  ha_rows get_curr_rownum()
+  ha_rows get_curr_rownum() const
   {
     return cursor.get_rownum();
   }
 
+  bool is_outside_computation_bounds() const
+  {
+    if (end_of_partition)
+      return true;
+    return false;
+  }
+
 private:
   void walk_till_non_peer()
   {
+    if (cursor.fetch()) // ERROR
+      return;
+    // Current row is not a peer.
+    if (order_direction * range_expr->cmp_read_only() <= 0)
+      return;
+    remove_value_from_items();
+
     int res;
-    while (!(res= cursor.get_next()))
+    while (!(res= cursor.next()))
     {
+      /* Note, no need to fetch the value explicitly here. The partition
+         read cursor will fetch it to check if the partition has changed.
+         TODO(cvicentiu) make this piece of information not necessary by
+         reimplementing Partition_read_cursor.
+      */
       if (order_direction * range_expr->cmp_read_only() <= 0)
         break;
       remove_value_from_items();
@@ -1009,6 +1032,7 @@ private:
     if (res)
       end_of_partition= true;
   }
+
 };
 
 
@@ -1049,7 +1073,7 @@ public:
                        SQL_I_List<ORDER> *order_list,
                        bool is_preceding_arg, Item *n_val_arg) :
     cursor(thd, partition_list), n_val(n_val_arg), item_add(NULL),
-    is_preceding(is_preceding_arg)
+    is_preceding(is_preceding_arg), added_values(false)
   {
     DBUG_ASSERT(order_list->elements == 1);
     Item *src_expr= order_list->first->item[0];
@@ -1085,6 +1109,7 @@ public:
 
     cursor.on_next_partition(rownum);
     end_of_partition= false;
+    added_values= false;
   }
 
   void next_partition(ha_rows rownum)
@@ -1109,25 +1134,38 @@ public:
         (prev_row + n) >= R
       We need to check about the current row.
     */
-    if (cursor.restore_last_row())
-    {
-      if (order_direction * range_expr->cmp_read_only() < 0)
-        return;
-      add_value_to_items();
-    }
     walk_till_non_peer();
   }
 
-  ha_rows get_curr_rownum()
+  bool is_outside_computation_bounds() const
   {
-    return cursor.get_rownum();
+    if (!added_values)
+      return true;
+    return false;
+  }
+
+  ha_rows get_curr_rownum() const
+  {
+    if (end_of_partition)
+      return cursor.get_rownum(); // Cursor does not pass over partition bound.
+    else
+      return cursor.get_rownum() - 1; // Cursor is placed on first non peer.
   }
 
 private:
+  bool added_values;
+
   void walk_till_non_peer()
   {
+    cursor.fetch();
+    // Current row is not a peer.
+    if (order_direction * range_expr->cmp_read_only() < 0)
+      return;
+
+    add_value_to_items(); // Add current row.
+    added_values= true;
     int res;
-    while (!(res= cursor.get_next()))
+    while (!(res= cursor.next()))
     {
       if (order_direction * range_expr->cmp_read_only() < 0)
         break;
@@ -1179,11 +1217,8 @@ public:
     // Save the value of the current_row
     peer_tracker.check_if_next_group();
     cursor.on_next_partition(rownum);
-    if (rownum != 0)
-    {
-      // Add the current row now because our cursor has already seen it
-      add_value_to_items();
-    }
+    // Add the current row now because our cursor has already seen it
+    add_value_to_items();
   }
 
   void next_partition(ha_rows rownum)
@@ -1194,8 +1229,6 @@ public:
   void pre_next_row()
   {
     dont_move= !peer_tracker.check_if_next_group();
-    if (!dont_move)
-      add_value_to_items();
   }
 
   void next_row()
@@ -1213,7 +1246,7 @@ public:
     walk_till_non_peer();
   }
 
-  ha_rows get_curr_rownum()
+  ha_rows get_curr_rownum() const
   {
     return cursor.get_rownum();
   }
@@ -1225,10 +1258,14 @@ private:
       Walk forward until we've met first row that's not a peer of the current
       row
     */
-    while (!cursor.get_next())
+    while (!cursor.next())
     {
       if (peer_tracker.compare_with_cache())
+      {
+        cursor.prev(); // Move to our peer.
         break;
+      }
+
       add_value_to_items();
     }
   }
@@ -1278,7 +1315,7 @@ public:
   {
     // Fetch the value from the first row
     peer_tracker.check_if_next_group();
-    cursor.move_to(rownum+1);
+    cursor.move_to(rownum);
   }
 
   void next_partition(ha_rows rownum) {}
@@ -1298,17 +1335,17 @@ public:
         Our cursor is pointing at the first row that was a peer of the previous
         current row. Or, it was the first row in the partition.
       */
-      if (cursor.restore_last_row())
-      {
-        // todo: need the following check ?
-        if (!peer_tracker.compare_with_cache())
-          return;
-        remove_value_from_items();
-      }
+      if (cursor.fetch())
+        return;
+
+      // todo: need the following check ?
+      if (!peer_tracker.compare_with_cache())
+        return;
+      remove_value_from_items();
 
       do
       {
-        if (cursor.get_next())
+        if (cursor.next() || cursor.fetch())
           return;
         if (!peer_tracker.compare_with_cache())
           return;
@@ -1318,7 +1355,7 @@ public:
     }
   }
 
-  ha_rows get_curr_rownum()
+  ha_rows get_curr_rownum() const
   {
     return cursor.get_rownum();
   }
@@ -1357,7 +1394,7 @@ public:
     /* Do nothing, UNBOUNDED PRECEDING frame end doesn't move. */
   }
 
-  ha_rows get_curr_rownum()
+  ha_rows get_curr_rownum() const
   {
     return curr_rownum;
   }
@@ -1394,16 +1431,12 @@ public:
 
   void next_partition(ha_rows rownum)
   {
-    if (!rownum)
-    {
-      /* Read the first row */
-      if (cursor.get_next())
-        return;
-    }
+    /* Activate the first row */
+    cursor.fetch();
     add_value_to_items();
 
     /* Walk to the end of the partition, updating the SUM function */
-    while (!cursor.get_next())
+    while (!cursor.next())
     {
       add_value_to_items();
     }
@@ -1414,7 +1447,7 @@ public:
     /* Do nothing, UNBOUNDED FOLLOWING frame end doesn't move */
   }
 
-  ha_rows get_curr_rownum()
+  ha_rows get_curr_rownum() const
   {
     return cursor.get_rownum();
   }
@@ -1432,16 +1465,12 @@ public:
   void next_partition(ha_rows rownum)
   {
     ha_rows num_rows_in_partition= 0;
-    if (!rownum)
-    {
-      /* Read the first row */
-      if (cursor.get_next())
-        return;
-    }
+    if (cursor.fetch())
+      return;
     num_rows_in_partition++;
 
     /* Walk to the end of the partition, find how many rows there are. */
-    while (!cursor.get_next())
+    while (!cursor.next())
       num_rows_in_partition++;
 
     List_iterator_fast<Item_sum> it(sum_functions);
@@ -1454,7 +1483,7 @@ public:
     }
   }
 
-  ha_rows get_curr_rownum()
+  ha_rows get_curr_rownum() const
   {
     return cursor.get_rownum();
   }
@@ -1474,12 +1503,12 @@ class Frame_n_rows_preceding : public Frame_cursor
   const ha_rows n_rows;
 
   /* Number of rows that we need to skip before our cursor starts moving */
-  ha_rows n_rows_to_skip;
+  ha_rows n_rows_behind;
 
   Table_read_cursor cursor;
 public:
   Frame_n_rows_preceding(bool is_top_bound_arg, ha_rows n_rows_arg) :
-    is_top_bound(is_top_bound_arg), n_rows(n_rows_arg)
+    is_top_bound(is_top_bound_arg), n_rows(n_rows_arg), n_rows_behind(0)
   {}
 
   void init(READ_RECORD *info)
@@ -1493,8 +1522,9 @@ public:
       Position our cursor to point at the first row in the new partition
       (for rownum=0, it is already there, otherwise, it lags behind)
     */
-    if (rownum != 0)
-      cursor.move_to(rownum);
+    cursor.move_to(rownum);
+    /* Cursor is in the same spot as current row. */
+    n_rows_behind= 0;
 
     /*
       Suppose the bound is ROWS 2 PRECEDING, and current row is row#n:
@@ -1508,37 +1538,65 @@ public:
         - bottom bound should add row #(n-2) into the window function
         - top bound should remove row (#n-3) from the window function.
     */
-    n_rows_to_skip= n_rows + (is_top_bound? 1:0) - 1;
+    move_cursor_if_possible();
 
-    /* Bottom bound "ROWS 0 PRECEDING" is a special case: */
-    if (n_rows_to_skip == ha_rows(-1))
-    {
-      cursor.get_next();
-      add_value_to_items();
-      n_rows_to_skip= 0;
-    }
   }
 
   void next_row()
   {
-    if (n_rows_to_skip)
+    n_rows_behind++;
+    move_cursor_if_possible();
+  }
+
+  bool is_outside_computation_bounds() const
+  {
+    /* As a bottom boundary, rows have not yet been added. */
+    if (!is_top_bound && n_rows - n_rows_behind)
+      return true;
+    return false;
+  }
+
+  ha_rows get_curr_rownum() const
+  {
+    return cursor.get_rownum();
+  }
+
+private:
+  void move_cursor_if_possible()
+  {
+    int rows_difference= n_rows - n_rows_behind;
+    if (rows_difference > 0) /* We still have to wait. */
+      return;
+
+      /* The cursor points to the first row in the frame. */
+    if (rows_difference == 0)
     {
-      n_rows_to_skip--;
+      if (!is_top_bound)
+      {
+        cursor.fetch();
+        add_value_to_items();
+      }
+      /* For top bound we don't have to remove anything as nothing was added. */
       return;
     }
 
-    if (cursor.get_next())
-      return;  // this is not expected to happen.
+    /* We need to catch up by one row. */
+    DBUG_ASSERT(rows_difference == -1);
 
-    if (is_top_bound) // this is frame start endpoint
+    if (is_top_bound)
+    {
+      cursor.fetch();
       remove_value_from_items();
+      cursor.next();
+    }
     else
+    {
+      cursor.next();
+      cursor.fetch();
       add_value_to_items();
-  }
-
-  ha_rows get_curr_rownum()
-  {
-    return cursor.get_rownum();
+    }
+    /* We've advanced one row. We are no longer behind. */
+    n_rows_behind--;
   }
 };
 
@@ -1559,6 +1617,7 @@ public:
   void pre_next_partition(ha_rows rownum)
   {
     add_value_to_items();
+    curr_rownum= rownum;
   }
 
   void next_partition(ha_rows rownum) {}
@@ -1574,7 +1633,7 @@ public:
     curr_rownum++;
   };
 
-  ha_rows get_curr_rownum()
+  ha_rows get_curr_rownum() const
   {
     return curr_rownum;
   }
@@ -1643,56 +1702,197 @@ public:
     at_partition_end= false;
 
     cursor.on_next_partition(rownum);
-
-    if (rownum != 0)
-    {
-      // This is only needed for "FOLLOWING 1". It is one row behind
-      cursor.move_to(rownum+1);
-
-      // Current row points at the first row in the partition
-      if (is_top_bound) // this is frame top endpoint
-        remove_value_from_items();
-      else
-        add_value_to_items();
-    }
   }
 
   /* Move our cursor to be n_rows ahead.  */
   void next_partition(ha_rows rownum)
   {
-    ha_rows i_end= n_rows + ((rownum==0)?1:0)- is_top_bound;
-    for (ha_rows i= 0; i < i_end; i++)
-    {
-      if (next_row_intern())
-        break;
-    }
+    if (is_top_bound)
+      next_part_top(rownum);
+    else
+      next_part_bottom(rownum);
   }
 
   void next_row()
   {
-    if (at_partition_end)
-      return;
-    next_row_intern();
+    if (is_top_bound)
+      next_row_top();
+    else
+      next_row_bottom();
   }
 
-  ha_rows get_curr_rownum()
+  bool is_outside_computation_bounds() const
+  {
+    /*
+       The top bound can go over the current partition. In this case,
+       the sum function has 0 values added to it.
+    */
+    if (at_partition_end && is_top_bound)
+      return true;
+    return false;
+  }
+
+  ha_rows get_curr_rownum() const
   {
     return cursor.get_rownum();
   }
 
 private:
-  bool next_row_intern()
+  void next_part_top(ha_rows rownum)
   {
-    if (!cursor.get_next())
+    for (ha_rows i= 0; i < n_rows; i++)
     {
-      if (is_top_bound) // this is frame start endpoint
-        remove_value_from_items();
-      else
-        add_value_to_items();
+      if (cursor.fetch())
+        break;
+      remove_value_from_items();
+      if (cursor.next())
+        at_partition_end= true;
     }
-    else
+  }
+
+  void next_part_bottom(ha_rows rownum)
+  {
+    if (cursor.fetch())
+      return;
+    add_value_to_items();
+
+    for (ha_rows i= 0; i < n_rows; i++)
+    {
+      if (cursor.next())
+      {
+        at_partition_end= true;
+        break;
+      }
+      add_value_to_items();
+    }
+    return;
+  }
+
+  void next_row_top()
+  {
+    if (cursor.fetch()) // PART END OR FAILURE
+    {
       at_partition_end= true;
-    return at_partition_end;
+      return;
+    }
+    remove_value_from_items();
+    if (cursor.next())
+    {
+      at_partition_end= true;
+      return;
+    }
+  }
+
+  void next_row_bottom()
+  {
+    if (at_partition_end)
+      return;
+
+    if (cursor.next())
+    {
+      at_partition_end= true;
+      return;
+    }
+
+    add_value_to_items();
+
+  }
+};
+
+/*
+  A cursor that performs a table scan between two indices. The indices
+  are provided by the two cursors representing the top and bottom bound
+  of the window function's frame definition.
+
+  Each scan clears the sum function.
+
+  NOTE:
+    The cursor does not alter the top and bottom cursors.
+    This type of cursor is expensive computational wise. This is only to be
+    used when the sum functions do not support removal.
+*/
+class Frame_scan_cursor : public Frame_cursor
+{
+public:
+  Frame_scan_cursor(const Frame_cursor &top_bound,
+                    const Frame_cursor &bottom_bound) :
+    top_bound(top_bound), bottom_bound(bottom_bound) {}
+
+  void init(READ_RECORD *info)
+  {
+    cursor.init(info);
+  }
+
+  void pre_next_partition(ha_rows rownum)
+  {
+    /* TODO(cvicentiu) Sum functions get cleared on next partition anyway during
+       the window function computation algorithm. Either perform this only in
+       cursors, or remove it from pre_next_partition.
+    */
+    curr_rownum= rownum;
+    clear_sum_functions();
+  }
+
+  void next_partition(ha_rows rownum)
+  {
+    compute_values_for_current_row();
+  }
+
+  void pre_next_row()
+  {
+    clear_sum_functions();
+  }
+
+  void next_row()
+  {
+    curr_rownum++;
+    compute_values_for_current_row();
+  }
+
+  ha_rows get_curr_rownum() const
+  {
+    return curr_rownum;
+  }
+
+private:
+  const Frame_cursor &top_bound;
+  const Frame_cursor &bottom_bound;
+  Table_read_cursor cursor;
+  ha_rows curr_rownum;
+
+  /* Clear all sum functions handled by this cursor. */
+  void clear_sum_functions()
+  {
+    List_iterator_fast<Item_sum> iter_sum_func(sum_functions);
+    Item_sum *sum_func;
+    while ((sum_func= iter_sum_func++))
+    {
+      sum_func->clear();
+    }
+  }
+
+  /* Scan the rows between the top bound and bottom bound. Add all the values
+     between them, top bound row  and bottom bound row inclusive. */
+  void compute_values_for_current_row()
+  {
+    if (top_bound.is_outside_computation_bounds() ||
+        bottom_bound.is_outside_computation_bounds())
+      return;
+
+    ha_rows start_rownum= top_bound.get_curr_rownum();
+    ha_rows bottom_rownum= bottom_bound.get_curr_rownum();
+    DBUG_PRINT("info", ("COMPUTING (%llu %llu)", start_rownum, bottom_rownum));
+
+    cursor.move_to(start_rownum);
+
+    for (ha_rows idx= start_rownum; idx <= bottom_rownum; idx++)
+    {
+      if (cursor.fetch()) //EOF
+        break;
+      add_value_to_items();
+      if (cursor.next()) // EOF
+        break;
+    }
   }
 };
 
@@ -1836,6 +2036,20 @@ void add_extra_frame_cursors(THD *thd, Cursor_manager *cursor_manager,
 }
 
 
+static bool is_computed_with_remove(Item_sum::Sumfunctype sum_func)
+{
+  switch (sum_func)
+  {
+    case Item_sum::CUME_DIST_FUNC:
+    case Item_sum::ROW_NUMBER_FUNC:
+    case Item_sum::RANK_FUNC:
+    case Item_sum::DENSE_RANK_FUNC:
+    case Item_sum::NTILE_FUNC:
+      return false;
+    default:
+      return true;
+  }
+}
 /*
    Create required frame cursors for the list of window functions.
    Register all functions to their appropriate cursors.
@@ -1896,6 +2110,17 @@ void get_window_functions_required_cursors(
     */
     cursor_manager->add_cursor(frame_bottom);
     cursor_manager->add_cursor(frame_top);
+    if (is_computed_with_remove(sum_func->sum_func()) &&
+        !sum_func->supports_removal())
+    {
+      frame_bottom->set_no_action();
+      frame_top->set_no_action();
+      Frame_cursor *scan_cursor= new Frame_scan_cursor(*frame_top,
+                                                       *frame_bottom);
+      scan_cursor->add_sum_func(sum_func);
+      cursor_manager->add_cursor(scan_cursor);
+
+    }
     cursor_managers->push_back(cursor_manager);
   }
 }