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.

2 files changed, 6 insertions, 4 deletions

diff --git a/storage/federatedx/ha_federatedx.cc b/storage/federatedx/ha_federatedx.cc
index b76391dae4e..fef349bbaaf 100644
--- a/storage/federatedx/ha_federatedx.cc
+++ b/storage/federatedx/ha_federatedx.cc
@@ -1731,8 +1731,10 @@ static void free_share(federatedx_txn *txn, FEDERATEDX_SHARE *share)
 }
 
 
-ha_rows ha_federatedx::records_in_range(uint inx, key_range *start_key,
-                                       key_range *end_key)
+ha_rows ha_federatedx::records_in_range(uint inx,
+                                        const key_range *start_key,
+                                        const key_range *end_key,
+                                        page_range *pages)
 {
   /*
 
diff --git a/storage/federatedx/ha_federatedx.h b/storage/federatedx/ha_federatedx.h
index 1870a83d13d..a62456e1c33 100644
--- a/storage/federatedx/ha_federatedx.h
+++ b/storage/federatedx/ha_federatedx.h
@@ -435,8 +435,8 @@ public:
   int delete_all_rows(void);
   int create(const char *name, TABLE *form,
              HA_CREATE_INFO *create_info);                      //required
-  ha_rows records_in_range(uint inx, key_range *start_key,
-                                   key_range *end_key);
+  ha_rows records_in_range(uint inx, const key_range *start_key,
+                           const key_range *end_key, page_range *pages);
   uint8 table_cache_type() { return HA_CACHE_TBL_NOCACHE; }
 
   THR_LOCK_DATA **store_lock(THD *thd, THR_LOCK_DATA **to,