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, 3 insertions, 2 deletions

diff --git a/include/heap.h b/include/heap.h
index b734f8ae88d..f0ac527976c 100644
--- a/include/heap.h
+++ b/include/heap.h
@@ -239,8 +239,9 @@ extern int heap_disable_indexes(HP_INFO *info);
 extern int heap_enable_indexes(HP_INFO *info);
 extern int heap_indexes_are_disabled(HP_INFO *info);
 extern void heap_update_auto_increment(HP_INFO *info, const uchar *record);
-ha_rows hp_rb_records_in_range(HP_INFO *info, int inx, key_range *min_key,
-                               key_range *max_key);
+ha_rows hp_rb_records_in_range(HP_INFO *info, int inx,
+                               const key_range *min_key,
+                               const key_range *max_key);
 int hp_panic(enum ha_panic_function flag);
 int heap_rkey(HP_INFO *info, uchar *record, int inx, const uchar *key,
               key_part_map keypart_map, enum ha_rkey_function find_flag);