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.

1 files changed, 4 insertions, 2 deletions

diff --git a/storage/federated/ha_federated.cc b/storage/federated/ha_federated.cc
index b87c5c39c37..00168791d35 100644
--- a/storage/federated/ha_federated.cc
+++ b/storage/federated/ha_federated.cc
@@ -1603,8 +1603,10 @@ static int free_share(FEDERATED_SHARE *share)
 }
 
 
-ha_rows ha_federated::records_in_range(uint inx, key_range *start_key,
-                                       key_range *end_key)
+ha_rows ha_federated::records_in_range(uint inx,
+                                       const key_range *start_key,
+                                       const key_range *end_key,
+                                       page_range *pages)
 {
   /*