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, 1 deletions

diff --git a/include/maria.h b/include/maria.h
index 2c711b0d31d..a4c425ced47 100644
--- a/include/maria.h
+++ b/include/maria.h
@@ -324,7 +324,9 @@ extern int maria_extra(MARIA_HA *file,
 		       enum ha_extra_function function, void *extra_arg);
 extern int maria_reset(MARIA_HA *file);
 extern ha_rows maria_records_in_range(MARIA_HA *info, int inx,
-				      key_range *min_key, key_range *max_key);
+                                      const key_range *min_key,
+                                      const key_range *max_key,
+                                      page_range *page);
 extern int maria_is_changed(MARIA_HA *info);
 extern int maria_delete_all_rows(MARIA_HA *info);
 extern uint maria_get_pointer_length(ulonglong file_length, uint def);