Added page_range to records_in_range() to improve range statistics

Prototype change:
-  virtual ha_rows records_in_range(uint inx, key_range *min_key,
-                                   key_range *max_key)
+  virtual ha_rows records_in_range(uint inx, const key_range *min_key,
+                                   const key_range *max_key,
+                                   page_range *res)

The handler can ignore the page_range parameter. In the case the handler
updates the parameter, the optimizer can deduce the following:
- If previous range's last key is on the same block as next range's first
  key
- If the current key range is in one block
- We can also assume that the first and last block read are cached!
  This can be used for a better calculation of IO seeks when we
  estimate the cost of a range index scan.

The parameter is fully implemented for MyISAM, Aria and InnoDB.
A separate patch will update handler::multi_range_read_info_const() to
take the benefits of this change and also remove the double
records_in_range() calls that are not anymore needed.

3 files changed, 17 insertions, 6 deletions

diff --git a/storage/myisammrg/ha_myisammrg.cc b/storage/myisammrg/ha_myisammrg.cc
index 4fd63020c6a..2a7ca8d51f8 100644
--- a/storage/myisammrg/ha_myisammrg.cc
+++ b/storage/myisammrg/ha_myisammrg.cc
@@ -1216,11 +1216,14 @@ void ha_myisammrg::position(const uchar *record)
 }
 
 
-ha_rows ha_myisammrg::records_in_range(uint inx, key_range *min_key,
-                                       key_range *max_key)
+ha_rows ha_myisammrg::records_in_range(uint inx,
+                                       const key_range *min_key,
+                                       const key_range *max_key,
+                                       page_range *pages)
 {
   DBUG_ASSERT(this->file->children_attached);
-  return (ha_rows) myrg_records_in_range(file, (int) inx, min_key, max_key);
+  return (ha_rows) myrg_records_in_range(file, (int) inx, min_key, max_key,
+                                         pages);
 }
 
 
diff --git a/storage/myisammrg/ha_myisammrg.h b/storage/myisammrg/ha_myisammrg.h
index b7cbd6c7d12..d5d62a002aa 100644
--- a/storage/myisammrg/ha_myisammrg.h
+++ b/storage/myisammrg/ha_myisammrg.h
@@ -129,7 +129,8 @@ public:
   int rnd_next(uchar *buf);
   int rnd_pos(uchar * buf, uchar *pos);
   void position(const uchar *record);
-  ha_rows records_in_range(uint inx, key_range *min_key, key_range *max_key);
+  ha_rows records_in_range(uint inx, const key_range *start_key,
+                           const key_range *end_key, page_range *pages);
   int delete_all_rows();
   int info(uint);
   int reset(void);
diff --git a/storage/myisammrg/myrg_range.c b/storage/myisammrg/myrg_range.c
index 893bda20833..da5e2c38d68 100644
--- a/storage/myisammrg/myrg_range.c
+++ b/storage/myisammrg/myrg_range.c
@@ -17,14 +17,21 @@
 #include "myrg_def.h"
 
 ha_rows myrg_records_in_range(MYRG_INFO *info, int inx,
-                              key_range *min_key, key_range *max_key)
+                              const key_range *min_key,
+                              const key_range *max_key,
+                              page_range *pages)
 {
   ha_rows records=0, res;
   MYRG_TABLE *table;
+  page_range ignore_pages;
+
+  /* Don't calculate pages of more than one active partition */
+  if (info->open_tables +1 != info->end_table)
+    pages= &ignore_pages;
 
   for (table=info->open_tables ; table != info->end_table ; table++)
   {
-    res= mi_records_in_range(table->table, inx, min_key, max_key);
+    res= mi_records_in_range(table->table, inx, min_key, max_key, pages);
     if (res == HA_POS_ERROR)
       return HA_POS_ERROR; 
     if (records > HA_POS_ERROR - res)