MDEV-40388: sequence.simple fails on replay

When the recording is enabled for the query,
explain select * from seq_15_to_1_step_12345;
it recorded the table context having a DDL definition as: -

CREATE TABLE `seq_15_to_1_step_12345` (
    ->   `seq` bigint(20) unsigned NOT NULL,
    ->   PRIMARY KEY (`seq`)
    -> ) ENGINE=SEQUENCE DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_uca1400_ai_ci;

Now, when that context is replayed, the DDL statement is executed.
But, we cannot create such the table and instead it errors out saying
ERROR 1050 (42S01): Table 'seq_15_to_1_step_12345' already exists.

The problem is that,
sequence table was determined using tbl->table->s->sequence. The
intention was to not record sequence table information. However, the
check was only partially correct.

Instead, we could compare using the engine name like
if (!tbl->is_view() && tbl->table)
{
  handlerton *hton= tbl->table->file->partition_ht();
  const LEX_CSTRING *engine_name= hton_name(hton);
  if (strcmp(engine_name->str, "SEQUENCE") == 0 ||
      strcmp(engine_name->str, "SQL_SEQUENCE") == 0)
    continue;
}

This makes both the following kinds of queries on sequences, to not
record any table contexts on them: -
1. explain select * from seq_15_to_1_step_12345;
2. create sequence s1;
   EXPLAIN select * from s1;

Author: bsrikanth-mariadb

mysql-test/main/opt_context_store_stats.result

@@ -591,3 +591,21 @@ table_name	file_stat_records	index_name	rec_per_key
 index_name	ranges	num_rows	max_index_blocks	max_row_blocks
 # == End of optimizer context
 drop table s1;
+#
+# MDEV-40388: sequence.simple fails on replay
+# Table context should *not* be recorded for seq
+#
+set optimizer_record_context=ON;
+explain select * from seq_15_to_1_step_12345;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	seq_15_to_1_step_12345	ALL	NULL	NULL	NULL	NULL	1	
+# == Optimizer Context
+# === Tables
+# Tables in the context
+table_name	file_stat_records	index_name	rec_per_key
+# === Range accesses
+index_name	ranges	num_rows	max_index_blocks	max_row_blocks
+# == End of optimizer context
+#
+# End of 13.1 tests
+#

mysql-test/main/opt_context_store_stats.test

@@ -432,3 +432,16 @@ EXPLAIN select * from s1;
 
 --source include/opt_context_list_tables_and_ranges.inc
 drop table s1;
+
+--echo #
+--echo # MDEV-40388: sequence.simple fails on replay
+--echo # Table context should *not* be recorded for seq
+--echo #
+set optimizer_record_context=ON;
+explain select * from seq_15_to_1_step_12345;
+
+--source include/opt_context_list_tables_and_ranges.inc
+
+--echo #
+--echo # End of 13.1 tests
+--echo #

sql/opt_context_store_replay.cc

@@ -746,8 +746,16 @@ bool Optimizer_context_recorder::dump_sql_script(THD* thd, String &sql_script)
     /*
       Sequence table doesn't need CREATE TABLE or contain any stats
     */
-    if (tbl->table && tbl->table->s && tbl->table->s->sequence)
-      continue;
+    if (!tbl->is_view() && tbl->table && tbl->table->file)
+    {
+      handlerton *hton= tbl->table->file->partition_ht();
+      const LEX_CSTRING *engine_name= hton_name(hton);
+      if (lex_string_eq(engine_name, STRING_WITH_LEN("SEQUENCE")) ||
+          lex_string_eq(engine_name, STRING_WITH_LEN("SQL_SEQUENCE")))
+      {
+        continue;
+      }
+    }
 
     /*
       A query can use the same table multiple times. Do not dump the