MDEV-20900: IN predicate to IN subquery conversion causes performance regression

Disable the IN predicate to IN subquery conversion when the types on the left and
right hand side of the IN predicate are not of comparable type.

1 files changed, 55 insertions, 1 deletions

diff --git a/sql/sql_tvc.cc b/sql/sql_tvc.cc
index 816c6fe1089..b4538248e07 100644
--- a/sql/sql_tvc.cc
+++ b/sql/sql_tvc.cc
@@ -796,6 +796,38 @@ bool Item_subselect::wrap_tvc_into_select(THD *thd, st_select_lex *tvc_sl)
 }
 
 
+/*
+  @brief
+   Check whether the items are of comparable type or not
+
+  @details
+    This check are done because materialization is not performed
+    if the left expr and right expr are of the same types.
+    @see subquery_types_allow_materialization()
+
+  @retval
+   0 comparable
+   1 not comparable
+*/
+
+static bool cmp_row_types(Item* item1, Item* item2)
+{
+  uint n= item1->cols();
+  if (item2->check_cols(n))
+    return true;
+
+  for (uint i=0; i < n; i++)
+  {
+    Item *inner= item1->element_index(i);
+    Item *outer= item2->element_index(i);
+    if (!inner->type_handler()->subquery_type_allows_materialization(inner,
+                                                                     outer))
+      return true;
+  }
+  return false;
+}
+
+
 /**
   @brief
     Transform IN predicate into IN subquery
@@ -840,10 +872,22 @@ Item *Item_func_in::in_predicate_to_in_subs_transformer(THD *thd,
   /* SELECT_LEX object where the transformation is performed */
   SELECT_LEX *parent_select= lex->current_select;
   uint8 save_derived_tables= lex->derived_tables;
+
+  /*
+    Make sure that create_tmp_table will not fail due to too long keys.
+    Here the strategy would mainly use materialization, so we need to make
+    sure that the materialized table can be created.
+
+    The checks here are the same as in subquery_type_allows_materialization()
+  */
+  uint32 length= max_length_of_left_expr();
+  if (!length  || length > tmp_table_max_key_length() ||
+      args[0]->cols() > tmp_table_max_key_parts())
+    return this;
   
   for (uint i=1; i < arg_count; i++)
   {
-    if (!args[i]->const_item())
+    if (!args[i]->const_item() || cmp_row_types(args[0], args[i]))
       return this;
   }
 
@@ -948,6 +992,16 @@ err:
 }
 
 
+uint32 Item_func_in::max_length_of_left_expr()
+{
+  uint n= args[0]->cols();
+  uint32 length= 0;
+  for (uint i=0; i < n; i++)
+    length+= args[0]->element_index(i)->max_length;
+  return length;
+}
+
+
 /**
   @brief
     Check if this IN-predicate can be transformed in IN-subquery