Bug #36677952 - killing DDL on partitioned tables: Assertion failure: dict0dict.cc:1887:table->get_ref_count() == 0

SYMPTOM:
- There is a crash that is occuring in a scenario where multiple
connections are opened on mysql client with below operations are
ran continuously:
a) conn1 - create multiple tables
b) conn2 - 'replace into' and 'delete from' the tables
c) conn3 - 'alter table rebuild partition'
d) conn4 - kill all the connections where alter table is running

ROOT CAUSE:
- When kill is called, alter table goes into cleanup which leads
to removal of table from dict cache. table->get_ref_count() refers
to number of handles the table is opened from. The problem occurs
when the race condition is hit where server tries to remove table
from dict cache but the table's n_ref_count is >0.
- In dict_partitioned_table_remove_from_cache(), the if condition
compares strings of name and prev_tabl-> name only until length of
name. If name is t1 and prev_table is t123, it will recognize as
true and tries to remove t123 from dict cache.

SOLUTION:
- The idea is to check if prev_table->name starts with the name
with PART_SEPARATOR appended, so that it filters only those
partitions or subpartitions of table with "name" and removes
from dict cache.

Change-Id: Ibd66dbca37fcbca52dc3b27c46d21bafe908b994

Author: Vidhya Sree Rajuladevi

sql/sql_table.cc

@@ -13608,6 +13608,8 @@ static bool mysql_inplace_alter_table(
     close_temporary_table(thd, altered_table, true, false);
     rollback_needs_dict_cache_reset = true;
 
+    DEBUG_SYNC(thd, "alter_table_inplace_will_need_reset");
+
     /*
       Replace table definition in the data-dictionary.
 

storage/innobase/dict/dict0dict.cc

@@ -1983,6 +1983,8 @@ void dict_partitioned_table_remove_from_cache(const char *name) {
   ut_ad(dict_sys_mutex_own());
 
   size_t name_len = strlen(name);
+  const auto name_with_separator =
+      std::string{name, name_len} + dict_name::PART_SEPARATOR;
 
   for (uint32_t i = 0; i < hash_get_n_cells(dict_sys->table_id_hash); ++i) {
     dict_table_t *table;
@@ -2000,8 +2002,10 @@ void dict_partitioned_table_remove_from_cache(const char *name) {
         continue;
       }
 
-      if ((strncmp(name, prev_table->name.m_name, name_len) == 0) &&
-          dict_table_is_partition(prev_table)) {
+      /* Find all the partitions or subpartitions of table with name */
+      if (!strncmp(name_with_separator.data(), prev_table->name.m_name,
+                   name_with_separator.size())) {
+        ut_a(dict_table_is_partition(prev_table));
         btr_drop_ahi_for_table(prev_table);
         dict_table_remove_from_cache(prev_table);
       }