Assertion undo_no <= 1 in reset_and_truncate_undo during ALTER IGNORE on temporary table

--source include/have_innodb.inc

CREATE TEMPORARY TABLE t (c INT) ENGINE=INNODB;

INSERT INTO t (c) VALUES (0),(0);

ALTER IGNORE TABLE t CHANGE c c DOUBLE (0,0);

#cleanup 

DROP TABLE t;

mariadbd: /test/10.11_dbg/storage/innobase/handler/ha_innodb.cc:15817: void trx_t::reset_and_truncate_undo(const dict_table_t *): Assertion `undo_no <= 1' failed.

Core was generated by `/test/MD270226-mariadb-10.11.17-linux-x86_64-dbg/bin/mariadbd --no-defaults --m'.

Program terminated with signal SIGABRT, Aborted.

Download failed: Invalid argument.  Continuing without source file ./nptl/./nptl/pthread_kill.c.

#0  __pthread_kill_implementation (no_tid=0, signo=6, threadid=<optimized out>)at ./nptl/pthread_kill.c:44

[Current thread is 1 (LWP 3199156)]

#0  __pthread_kill_implementation (no_tid=0, signo=6, threadid=<optimized out>) at ./nptl/pthread_kill.c:44

#1  __pthread_kill_internal (signo=6, threadid=<optimized out>) at ./nptl/pthread_kill.c:78

#2  __GI___pthread_kill (threadid=<optimized out>, signo=signo@entry=6) at ./nptl/pthread_kill.c:89

#3  0x000072153524527e in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26

#4  0x00007215352288ff in __GI_abort () at ./stdlib/abort.c:79

#5  0x000072153522881b in __assert_fail_base (fmt=0x7215353d01e8 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", assertion=assertion@entry=0x64b4a4c2d8d3 "undo_no <= 1", file=file@entry=0x64b4a4c254b8 "/test/10.11_dbg/storage/innobase/handler/ha_innodb.cc", line=line@entry=15817, function=function@entry=0x64b4a4c2d8e0 "void trx_t::reset_and_truncate_undo(const dict_table_t *)") at ./assert/assert.c:96

#6  0x000072153523b517 in __assert_fail (assertion=0x64b4a4c2d8d3 "undo_no <= 1", file=0x64b4a4c254b8 "/test/10.11_dbg/storage/innobase/handler/ha_innodb.cc", line=15817, function=0x64b4a4c2d8e0 "void trx_t::reset_and_truncate_undo(const dict_table_t *)") at ./assert/assert.c:105

#7  0x000064b4a435d798 in trx_t::reset_and_truncate_undo (this=0x721534dffb80, table=0x721440054b30) at /test/10.11_dbg/storage/innobase/handler/ha_innodb.cc:15817

#8  0x000064b4a43422ab in ha_innobase::extra (this=0x72144003cf18, operation=HA_EXTRA_END_COPY) at /test/10.11_dbg/storage/innobase/handler/ha_innodb.cc:15927

#9  0x000064b4a3ca2156 in copy_data_between_tables (thd=0x721440000d58, from=0x72144018ae88, to=0x721440058d08, ignore=true, order_num=0, order=0x0, copied=0x721534323340, deleted=0x721534323338, alter_info=0x721534326120, alter_ctx=0x7215343241b8) at /test/10.11_dbg/sql/sql_table.cc:12475

#10 0x000064b4a3c981f4 in mysql_alter_table (thd=0x721440000d58, new_db=0x721440005908, new_name=0x721440005d68, create_info=0x721534326290, table_list=0x721440014778, recreate_info=0x721534325970, alter_info=0x721534326120, order_num=0, order=0x0, ignore=true, if_exists=false) at /test/10.11_dbg/sql/sql_table.cc:11597

#11 0x000064b4a3d57ade in Sql_cmd_alter_table::execute (this=0x721440014fc8, thd=0x721440000d58) at /test/10.11_dbg/sql/sql_alter.cc:688

#12 0x000064b4a3b80a19 in mysql_execute_command (thd=0x721440000d58, is_called_from_prepared_stmt=false) at /test/10.11_dbg/sql/sql_parse.cc:6201

#13 0x000064b4a3b6e754 in mysql_parse (thd=0x721440000d58, rawbuf=0x721440014670 "ALTER IGNORE TABLE t CHANGE c c DOUBLE (0,0)", length=44, parser_state=0x721534327ae0) at /test/10.11_dbg/sql/sql_parse.cc:8223

#14 0x000064b4a3b6bbf9 in dispatch_command (command=COM_QUERY, thd=0x721440000d58, packet=0x7214400a07a9 "", packet_length=44, blocking=true) at /test/10.11_dbg/sql/sql_parse.cc:1924

#15 0x000064b4a3b6f303 in do_command (thd=0x721440000d58, blocking=true) at /test/10.11_dbg/sql/sql_parse.cc:1434

#16 0x000064b4a3d4c9c9 in do_handle_one_connection (connect=0x64b4bb1c3648, put_in_cache=true) at /test/10.11_dbg/sql/sql_connect.cc:1475

#17 0x000064b4a3d4c762 in handle_one_connection (arg=0x64b4bb27bc18) at /test/10.11_dbg/sql/sql_connect.cc:1387

#18 0x000072153529caa4 in start_thread (arg=<optimized out>) at ./nptl/pthread_create.c:447

#19 0x0000721535329c6c in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:78

commit e5fed9eaf49419fe81d3695a4323816db1df8e32 (HEAD)

Author: Thirunarayanan Balathandayuthapani <thiru@mariadb.com>

Date:   Thu Feb 26 12:07:23 2026 +0530

    MDEV-36436  Assertion "unexpected references" == 0 after ALTER IGNORE TABLE

    Problem:

    =========

    An assertion failure occurs in InnoDB during consecutive

    ALTER TABLE operations using the COPY algorithm. The crash

    happens during the table rename phase because the

    source table (dict_table_t::n_ref_count) is non-zero, despite

    the thread holding an exclusive Metadata Lock (MDL).