Fix for bug #44738 "fill_schema_table_from_frm() opens tables without

lowercasing table name".

In lower_case_table_names > 0 mode some queries to I_S left entries
with incorrect key in table definition cache. This wasted memory and
caused some of the further queries to I_S to produce stale results
in cases when table definition was changed by a DDL statement.
Also in combination with similar problem in CREATE TABLE (which also
has peeked into table definition cache using non-normalized key) this
issue led to to spurious ER_TABLE_EXISTS_ERROR errors when one tried
to create a table with the same name as a previously existing but
dropped table (assuming that table name contained characters in upper
case).

This problem occured due to fact that fill_schema_table_from_frm()
was not properly normalizing (lowercasing) database and table names
which it used for lookups in table definition cache.

This fix adds proper normalization to this function. It also solves
similar problem in CREATE TABLE's code by ensuring that it uses
properly normalized version of table name when it peeks into table
definition cache instead of non-normalized one.

mysql-test/r/lowercase_table2.result:
  Added test for #44738 "fill_schema_table_from_frm() opens tables
  without lowercasing table name".
mysql-test/t/lowercase_table2.test:
  Added test for #44738 "fill_schema_table_from_frm() opens tables
  without lowercasing table name".
sql/sql_show.cc:
  Normalize database and table name before using them for looking
  up entry in table definition cache.
sql/sql_table.cc:
  Ensure that CREATE TABLE uses properly normalized version of table
  name when it peeks into table definition cache.

1 files changed, 21 insertions, 2 deletions

diff --git a/sql/sql_show.cc b/sql/sql_show.cc
index b16f050dea6..cf9203d0848 100644
--- a/sql/sql_show.cc
+++ b/sql/sql_show.cc
@@ -3078,12 +3078,31 @@ static int fill_schema_table_from_frm(THD *thd,TABLE *table,
   int error;
   char key[MAX_DBKEY_LENGTH];
   uint key_length;
+  char db_name_buff[NAME_LEN + 1], table_name_buff[NAME_LEN + 1];
 
   bzero((char*) &table_list, sizeof(TABLE_LIST));
   bzero((char*) &tbl, sizeof(TABLE));
 
-  table_list.table_name= table_name->str;
-  table_list.db= db_name->str;
+  if (lower_case_table_names)
+  {
+    /*
+      In lower_case_table_names > 0 metadata locking and table definition
+      cache subsystems require normalized (lowercased) database and table
+      names as input.
+    */
+    strmov(db_name_buff, db_name->str);
+    strmov(table_name_buff, table_name->str);
+    my_casedn_str(files_charset_info, db_name_buff);
+    my_casedn_str(files_charset_info, table_name_buff);
+    table_list.db= db_name_buff;
+    table_list.table_name= table_name_buff;
+  }
+  else
+  {
+    table_list.table_name= table_name->str;
+    table_list.db= db_name->str;
+  }
+
   key_length= create_table_def_key(thd, key, &table_list, 0);
   pthread_mutex_lock(&LOCK_open);
   share= get_table_share(thd, &table_list, key,