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, 7 insertions, 4 deletions

diff --git a/storage/rocksdb/ha_rocksdb.cc b/storage/rocksdb/ha_rocksdb.cc
index 3fa13295496..1b7ec9f9473 100644
--- a/storage/rocksdb/ha_rocksdb.cc
+++ b/storage/rocksdb/ha_rocksdb.cc
@@ -11910,8 +11910,9 @@ int ha_rocksdb::extra(enum ha_extra_function operation) {
   Given a starting key and an ending key, estimate the number of rows that
   will exist between the two keys.
 */
-ha_rows ha_rocksdb::records_in_range(uint inx, key_range *const min_key,
-                                     key_range *const max_key) {
+ha_rows ha_rocksdb::records_in_range(uint inx, const key_range *const min_key,
+                                     const key_range *const max_key,
+                                     page_range *pages) {
   DBUG_ENTER_FUNC();
 
   ha_rows ret = THDVAR(ha_thd(), records_in_range);
diff --git a/storage/rocksdb/ha_rocksdb.h b/storage/rocksdb/ha_rocksdb.h
index 426aa110597..1820326090f 100644
--- a/storage/rocksdb/ha_rocksdb.h
+++ b/storage/rocksdb/ha_rocksdb.h
@@ -902,8 +902,10 @@ public:
   int check(THD *const thd, HA_CHECK_OPT *const check_opt) override
       MY_ATTRIBUTE((__warn_unused_result__));
   int remove_rows(Rdb_tbl_def *const tbl);
-  ha_rows records_in_range(uint inx, key_range *const min_key,
-                           key_range *const max_key) override
+  ha_rows records_in_range(uint inx,
+                           const key_range *const min_key,
+                           const key_range *const max_key,
+                           page_range *pages) override
       MY_ATTRIBUTE((__warn_unused_result__));
 
   int delete_table(Rdb_tbl_def *const tbl);