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/myisam.h b/include/myisam.h
index dfd5676a4d8..0942584e874 100644
--- a/include/myisam.h
+++ b/include/myisam.h
@@ -291,7 +291,9 @@ extern int mi_extra(struct st_myisam_info *file,
 		    void *extra_arg);
 extern int mi_reset(struct st_myisam_info *file);
 extern ha_rows mi_records_in_range(MI_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);
 extern int mi_log(int activate_log);
 extern int mi_is_changed(struct st_myisam_info *info);
 extern int mi_delete_all_rows(struct st_myisam_info *info);