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, 2 deletions

diff --git a/storage/tokudb/ha_tokudb.cc b/storage/tokudb/ha_tokudb.cc
index f4808a49c49..2c980196c1b 100644
--- a/storage/tokudb/ha_tokudb.cc
+++ b/storage/tokudb/ha_tokudb.cc
@@ -7889,7 +7889,9 @@ double ha_tokudb::index_only_read_time(uint keynr, double records) {
 //      number > 0 - There are approximately number matching rows in the range
 //      HA_POS_ERROR - Something is wrong with the index tree
 //
-ha_rows ha_tokudb::records_in_range(uint keynr, key_range* start_key, key_range* end_key) {
+ha_rows ha_tokudb::records_in_range(uint keynr, const key_range* start_key,
+                                    const key_range* end_key,
+                                    page_range *pages) {
     TOKUDB_HANDLER_DBUG_ENTER("%d %p %p", keynr, start_key, end_key);
     DBT *pleft_key, *pright_key;
     DBT left_key, right_key;
diff --git a/storage/tokudb/ha_tokudb.h b/storage/tokudb/ha_tokudb.h
index ea082aa53f4..5a87bf936fd 100644
--- a/storage/tokudb/ha_tokudb.h
+++ b/storage/tokudb/ha_tokudb.h
@@ -844,7 +844,9 @@ public:
     int external_lock(THD * thd, int lock_type);
     int start_stmt(THD * thd, thr_lock_type lock_type);
 
-    ha_rows records_in_range(uint inx, key_range * min_key, key_range * max_key);
+    ha_rows records_in_range(uint inx, const key_range * min_key,
+                             const key_range * max_key,
+                             page_range *pages);
 
     uint32_t get_cursor_isolation_flags(enum thr_lock_type lock_type, THD* thd);
     THR_LOCK_DATA **store_lock(THD * thd, THR_LOCK_DATA ** to, enum thr_lock_type lock_type);