From 4f568ab503c91840779ac493f3c7f7bbbfa4fb57 Mon Sep 17 00:00:00 2001
From: Monty <monty@mariadb.org>
Date: Fri, 3 Jun 2022 13:24:18 +0300
Subject: Reduced size of POSITION

Replaced Cost_estimate prefix_cost with a double as prefix_cost was
only used to store and retrive total prefix cost.

This also speeds up things (a bit) as don't have to call
Cost_estimate::total_cost() for every access to the prefix_cost.

Sizeof POSITION decreased from 304 to 256.
---
 sql/opt_subselect.cc | 17 ++++++++---------
 sql/sql_select.cc    |  2 +-
 sql/sql_select.h     |  6 +++---
 3 files changed, 12 insertions(+), 13 deletions(-)

diff --git a/sql/opt_subselect.cc b/sql/opt_subselect.cc
index 3e58a2788c8..2440047638e 100644
--- a/sql/opt_subselect.cc
+++ b/sql/opt_subselect.cc
@@ -2895,7 +2895,7 @@ void optimize_semi_joins(JOIN *join, table_map remaining_tables, uint idx,
        pos[-1].inner_tables_handled_with_other_sjs;
   }
 
-  pos->prefix_cost.convert_from_cost(*current_read_time);
+  pos->prefix_cost= *current_read_time;
   pos->prefix_record_count= *current_record_count;
 
   {
@@ -3017,7 +3017,7 @@ void optimize_semi_joins(JOIN *join, table_map remaining_tables, uint idx,
 
   update_sj_state(join, new_join_tab, idx, remaining_tables);
 
-  pos->prefix_cost.convert_from_cost(*current_read_time);
+  pos->prefix_cost= *current_read_time;
   pos->prefix_record_count= *current_record_count;
   pos->dups_producing_tables= dups_producing_tables;
 }
@@ -3107,15 +3107,15 @@ bool Sj_materialization_picker::check_qep(JOIN *join,
     else
     {
       /* This is SJ-Materialization with lookups */
-      Cost_estimate prefix_cost; 
+      double prefix_cost;
       signed int first_tab= (int)idx - mat_info->tables;
-      double prefix_rec_count;
+      double prefix_rec_count, mat_read_time;
       Json_writer_object trace(join->thd);
       trace.add("strategy", "SJ-Materialization");
 
       if (first_tab < (int)join->const_tables)
       {
-        prefix_cost.reset();
+        prefix_cost= 0;
         prefix_rec_count= 1.0;
       }
       else
@@ -3124,9 +3124,8 @@ bool Sj_materialization_picker::check_qep(JOIN *join,
         prefix_rec_count= join->positions[first_tab].prefix_record_count;
       }
 
-      double mat_read_time= prefix_cost.total_cost();
       mat_read_time=
-        COST_ADD(mat_read_time,
+        COST_ADD(prefix_cost,
                  COST_ADD(mat_info->materialization_cost.total_cost(),
                           COST_MULT(prefix_rec_count,
                                     mat_info->lookup_cost.total_cost())));
@@ -3171,7 +3170,7 @@ bool Sj_materialization_picker::check_qep(JOIN *join,
     }
     else
     {
-      prefix_cost= join->positions[first_tab - 1].prefix_cost.total_cost();
+      prefix_cost= join->positions[first_tab - 1].prefix_cost;
       prefix_rec_count= join->positions[first_tab - 1].prefix_record_count;
     }
 
@@ -3535,7 +3534,7 @@ bool Duplicate_weedout_picker::check_qep(JOIN *join,
     }
     else
     {
-      dups_cost= join->positions[first_tab - 1].prefix_cost.total_cost();
+      dups_cost= join->positions[first_tab - 1].prefix_cost;
       prefix_rec_count= join->positions[first_tab - 1].prefix_record_count;
       temptable_rec_size= 8; /* This is not true but we'll make it so */
     }
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 0aea34fffb7..3b07122e7c1 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -17946,7 +17946,7 @@ void optimize_wo_join_buffering(JOIN *join, uint first_tab, uint last_tab,
 
   if (first_tab > join->const_tables)
   {
-    cost=      join->positions[first_tab - 1].prefix_cost.total_cost();
+    cost=      join->positions[first_tab - 1].prefix_cost;
     rec_count= join->positions[first_tab - 1].prefix_record_count;
   }
   else
diff --git a/sql/sql_select.h b/sql/sql_select.h
index 8e318503b18..46a359c746f 100644
--- a/sql/sql_select.h
+++ b/sql/sql_select.h
@@ -952,6 +952,9 @@ public:
 
   double    prefix_record_count;
 
+  /* Cost for the join prefix */
+  double prefix_cost;
+
   /*
     NULL  -  'index' or 'range' or 'index_merge' or 'ALL' access is used.
     Other - [eq_]ref[_or_null] access is used. Pointer to {t.keypart1 = expr}
@@ -983,9 +986,6 @@ public:
   LooseScan_picker          loosescan_picker;
   Sj_materialization_picker sjmat_picker;
 
-  /* Cumulative cost and record count for the join prefix */
-  Cost_estimate prefix_cost;
-
   /*
     Current optimization state: Semi-join strategy to be used for this
     and preceding join tables.
-- 
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