From 90ba999e800957c230290bd438a3e73628222a74 Mon Sep 17 00:00:00 2001
From: Sergei Petrunia <sergey@mariadb.com>
Date: Wed, 27 Jul 2022 17:37:03 +0300
Subject: [PATCH] MDEV-25020: Range optimizer regression for key IN (const,
 ....)

(addressed review input)
The issue was introduced by @@optimizer_max_sel_arg_weight code.
key_or() calls SEL_ARG::update_weight_locally().  That function
takes O(tree->elements) time.
Without that call, key_or(big_tree, one_element_tree) would take
O(log(big_tree)) when one_element_tree doesn't overlap with elements
of big_tree.
This means, update_weight_locally() can cause a big slowdown.

The fix:
1. key_or() actually doesn't need to call update_weight_locally().
  It calls SEL_ARG::tree_delete() and SEL_ARG::insert(). These functions
  update SEL_ARG::weight.
  It also manipulates the SEL_ARG objects directly, but these
  modifications do not change the weight of the tree.
  I've just removed the update_weight_locally() call.
2. and_all_keys() also calls update_weight_locally(). It manipulates the
  SEL_ARG graph directly.
  Removed that call and added the code to update the SEL_ARG graph weight.

Tests main.range and main.range_not_embedded already contain the queries
that have test coverage for the affected code.
---
 sql/opt_range.cc | 35 ++++++-----------------------------
 sql/opt_range.h  |  1 -
 2 files changed, 6 insertions(+), 30 deletions(-)

diff --git a/sql/opt_range.cc b/sql/opt_range.cc
index e3287e1bbea..1cc573f90f2 100644
--- a/sql/opt_range.cc
+++ b/sql/opt_range.cc
@@ -9855,12 +9855,14 @@ and_all_keys(RANGE_OPT_PARAM *param, SEL_ARG *key1, SEL_ARG *key2,
       return key2;
     key1->right= key1->left= &null_element;
     key1->next= key1->prev= 0;
+    key1->weight= 1 + (key1->next_key_part? key1->next_key_part->weight: 0);
   }
 
   for (next=key1->first(); next ; next=next->next)
   {
     if (next->next_key_part)
     {
+      uint old_weight= next->next_key_part->weight;
       SEL_ARG *tmp= key_and(param, next->next_key_part, key2, clone_flag);
       if (tmp && tmp->type == SEL_ARG::IMPOSSIBLE)
       {
@@ -9868,21 +9870,22 @@ and_all_keys(RANGE_OPT_PARAM *param, SEL_ARG *key1, SEL_ARG *key2,
 	continue;
       }
       next->next_key_part=tmp;
+      key1->weight+= (tmp? tmp->weight: 0) - old_weight;
       if (use_count)
 	next->increment_use_count(use_count);
       if (param->alloced_sel_args > SEL_ARG::MAX_SEL_ARGS)
         break;
     }
     else
+    {
       next->next_key_part=key2;
+      key1->weight += key2->weight;
+    }
   }
   if (!key1)
     return &null_element;			// Impossible ranges
   key1->use_count++;
 
-  /* Re-compute the result tree's weight. */
-  key1->update_weight_locally();
-
   key1->max_part_no= MY_MAX(key2->max_part_no, key2->part+1);
   return key1;
 }
@@ -10046,29 +10049,6 @@ get_range(SEL_ARG **e1,SEL_ARG **e2,SEL_ARG *root1)
   return 0;
 }
 
-/*
-  @brief
-    Update the tree weight.
-
-  @detail
-    Utility function to be called on a SEL_ARG tree root after doing local
-    modifications concerning changes at this key part.
-    Assumes that the weight of the graphs connected via next_key_part is
-    up to dayte.
-*/
-void SEL_ARG::update_weight_locally()
-{
-  uint new_weight= 0;
-  const SEL_ARG *sl;
-  for (sl= first(); sl ; sl= sl->next)
-  {
-    new_weight++;
-    if (sl->next_key_part)
-      new_weight += sl->next_key_part->weight;
-  }
-  weight= new_weight;
-}
-
 
 #ifndef DBUG_OFF
 /*
@@ -10828,9 +10808,6 @@ end:
   }
   key1->use_count++;
 
-  /* Re-compute the result tree's weight. */
-  key1->update_weight_locally();
-
   key1->max_part_no= max_part_no;
   return key1;
 }
diff --git a/sql/opt_range.h b/sql/opt_range.h
index 1014176ecc5..5594397e709 100644
--- a/sql/opt_range.h
+++ b/sql/opt_range.h
@@ -317,7 +317,6 @@ public:
   uint weight;
   enum { MAX_WEIGHT = 32000 };
 
-  void update_weight_locally();
 #ifndef DBUG_OFF
   uint verify_weight();
 #endif