cleanup: Don't pass THD to get_merge_many_buff_cost_fast

We can pass the cost directly.

Reviewer: Monty

sql/filesort.cc

@@ -1594,9 +1594,10 @@ static bool check_if_pq_applicable(Sort_param *param,
         scanning the table and comparing the rows with the where clause!
       */
       const double sort_merge_cost=
-        get_merge_many_buffs_cost_fast(table->in_use, num_rows,
+        get_merge_many_buffs_cost_fast(num_rows,
                                        num_available_keys,
-                                       (uint)row_length);
+                                       (uint)row_length,
+                                       ROWID_COMPARE_COST_THD(table->in_use));
       /*
         PQ has cost:
         (insert + qsort) * log(queue size) * ROWID_COMPARE_COST

sql/filesort_utils.cc

@@ -27,12 +27,15 @@ PSI_memory_key key_memory_Filesort_buffer_sort_keys;
   A local helper function. See comments for get_merge_buffers_cost().
 */
 
-static double get_merge_cost(double rowid_compare_cost, ha_rows num_elements,
-                      ha_rows num_buffers, uint elem_size)
+static
+double get_merge_cost(ha_rows num_elements,
+                      ha_rows num_buffers,
+                      uint elem_size,
+                      double key_compare_cost)
 {
   return (2.0 * ((double) num_elements * elem_size) / IO_SIZE
           + (double) num_elements * log((double) num_buffers) *
-          rowid_compare_cost / M_LN2);
+          key_compare_cost / M_LN2);
 }
 
 /**
@@ -43,19 +46,19 @@ static double get_merge_cost(double rowid_compare_cost, ha_rows num_elements,
   TODO: Use this function for Unique::get_use_cost().
 */
 
-double get_merge_many_buffs_cost_fast(THD *thd,
-                                      ha_rows num_rows,
+double get_merge_many_buffs_cost_fast(ha_rows num_rows,
                                       ha_rows num_keys_per_buffer,
-                                      uint    elem_size)
+                                      uint    elem_size,
+                                      double  key_compare_cost)
 {
   ha_rows num_buffers= num_rows / num_keys_per_buffer;
   ha_rows last_n_elems= num_rows % num_keys_per_buffer;
-  double total_cost, rowid_compare_cost= ROWID_COMPARE_COST_THD(thd);
+  double total_cost;
 
   // Calculate CPU cost of sorting buffers.
   total_cost=
     ((num_buffers * num_keys_per_buffer * log(1.0 + num_keys_per_buffer) +
-      last_n_elems * log(1.0 + last_n_elems)) * rowid_compare_cost);
+      last_n_elems * log(1.0 + last_n_elems)) * key_compare_cost);
 
   // Simulate behavior of merge_many_buff().
   while (num_buffers >= MERGEBUFF2)
@@ -69,16 +72,16 @@ double get_merge_many_buffs_cost_fast(THD *thd,
     // Cost of merge sort 'num_merge_calls'.
     total_cost+=
       num_merge_calls *
-      get_merge_cost(rowid_compare_cost, num_keys_per_buffer * MERGEBUFF,
-                     MERGEBUFF, elem_size);
+      get_merge_cost(num_keys_per_buffer * MERGEBUFF, MERGEBUFF, elem_size,
+                     key_compare_cost);
 
     // # of records in remaining buffers.
     last_n_elems+= num_remaining_buffs * num_keys_per_buffer;
 
     // Cost of merge sort of remaining buffers.
     total_cost+=
-      get_merge_cost(rowid_compare_cost, last_n_elems, 1 + num_remaining_buffs,
-                     elem_size);
+      get_merge_cost(last_n_elems, 1 + num_remaining_buffs, elem_size,
+                     key_compare_cost);
 
     num_buffers= num_merge_calls;
     num_keys_per_buffer*= MERGEBUFF;
@@ -86,8 +89,8 @@ double get_merge_many_buffs_cost_fast(THD *thd,
 
   // Simulate final merge_buff call.
   last_n_elems+= num_keys_per_buffer * num_buffers;
-  total_cost+= get_merge_cost(rowid_compare_cost, last_n_elems, 1 + num_buffers,
-                              elem_size);
+  total_cost+= get_merge_cost(last_n_elems, 1 + num_buffers, elem_size,
+                              key_compare_cost);
   return total_cost;
 }
 

sql/filesort_utils.h

@@ -20,12 +20,14 @@
 #include "sql_array.h"
 
 class Sort_param;
-/*
+
+/**
   Calculate cost of merge sort
 
     @param num_rows            Total number of rows.
     @param num_keys_per_buffer Number of keys per buffer.
     @param elem_size           Size of each element.
+    @param key_compare_cost    Cost to compare two keys during QSort & merge
 
     Calculates cost of merge sort by simulating call to merge_many_buff().
 
@@ -38,10 +40,10 @@ class Sort_param;
 
     See also comments get_merge_many_buffs_cost().
 */
-
-double get_merge_many_buffs_cost_fast(THD *thd, ha_rows num_rows,
+double get_merge_many_buffs_cost_fast(ha_rows num_rows,
                                       ha_rows num_keys_per_buffer,
-                                      uint    elem_size);
+                                      uint    elem_size,
+                                      double  key_compare_cost);
 
 
 /**