MDEV-29013 ER_KEY_NOT_FOUND/lock timeout upon online alter with long unique

1. ER_KEY_NOT_FOUND
general replcation problem, already fixed earlier.
test added.

2. ER_LOCK_WAIT_TIMEOUT
This is a long unique specific problem.

Sometimes, lookup_handler is created for to->file. To properly free it,
ha_reset should be called. It is usually done by calling
close_thread_table, but ALTER TABLE makes it differently. Hence, a single
ha_reset call is added to mysql_alter_table.

Also, event_mem_root is removed. Normally, no per-event data should be
allocated on thd->mem_root, that would mean a leak. And otherwise,
lookup_handler is lazily allocated, but its lifetime matches statement,
not event.

mysql-test/main/alter_table_online_debug.result

@@ -918,5 +918,39 @@ a	b
 drop table t1;
 set debug_sync= 'reset';
 #
+# MDEV-29013 ER_KEY_NOT_FOUND/lock timeout upon online alter
+# with long unique indexes
+#
+create table t1 (b text not null, unique(b));
+insert into t1 values ('foo'),('bar');
+set debug_sync= 'now wait_for downgraded';
+connection con2;
+set debug_sync= 'alter_table_online_downgraded signal downgraded wait_for goforit';
+alter table t1 add c int, algorithm=copy, lock=none;
+connection default;
+delete from t1;
+set debug_sync= 'now signal goforit';
+connection con2;
+connection default;
+drop table t1;
+set debug_sync= reset;
+###
+create table t1 (a text, unique(a)) engine=innodb;
+create table t2 (b text, unique(b)) engine=innodb;
+insert into t2 values (null),(null);
+set debug_sync= 'now wait_for downgraded';
+connection con2;
+set debug_sync= 'alter_table_online_downgraded signal downgraded wait_for goforit';
+alter table t2 add column c int, algorithm=copy, lock=none;
+connection default;
+delete from t2;
+set debug_sync= 'now signal goforit';
+connection con2;
+connection default;
+alter table t2 force;
+alter table t1 force;
+drop table t1, t2;
+set debug_sync= reset;
+#
 # End of 11.2 tests
 #

mysql-test/main/alter_table_online_debug.test

@@ -1059,6 +1059,60 @@ select * from t1;
 drop table t1;
 set debug_sync= 'reset';
 
+--echo #
+--echo # MDEV-29013 ER_KEY_NOT_FOUND/lock timeout upon online alter
+--echo # with long unique indexes
+--echo #
+create table t1 (b text not null, unique(b));
+insert into t1 values ('foo'),('bar');
+--send
+set debug_sync= 'now wait_for downgraded';
+
+--connection con2
+set debug_sync= 'alter_table_online_downgraded signal downgraded wait_for goforit';
+--send
+alter table t1 add c int, algorithm=copy, lock=none;
+
+--connection default
+--reap
+delete from t1;
+set debug_sync= 'now signal goforit';
+
+--connection con2
+--reap
+
+--connection default
+drop table t1;
+set debug_sync= reset;
+
+--echo ###
+
+create table t1 (a text, unique(a)) engine=innodb;
+create table t2 (b text, unique(b)) engine=innodb;
+insert into t2 values (null),(null);
+--send
+set debug_sync= 'now wait_for downgraded';
+
+--connection con2
+set debug_sync= 'alter_table_online_downgraded signal downgraded wait_for goforit';
+--send
+alter table t2 add column c int, algorithm=copy, lock=none;
+
+--connection default
+--reap
+delete from t2;
+set debug_sync= 'now signal goforit';
+
+--connection con2
+--reap
+
+--connection default
+alter table t2 force;
+alter table t1 force;
+
+drop table t1, t2;
+set debug_sync= reset;
+
 --echo #
 --echo # End of 11.2 tests
 --echo #

sql/sql_table.cc

@@ -11556,12 +11556,6 @@ class Has_default_error_handler : public Internal_error_handler
 static int online_alter_read_from_binlog(THD *thd, rpl_group_info *rgi,
                                          Cache_flip_event_log *log)
 {
-  MEM_ROOT event_mem_root;
-  Query_arena backup_arena;
-  Query_arena event_arena(&event_mem_root, Query_arena::STMT_INITIALIZED);
-  init_sql_alloc(key_memory_gdl, &event_mem_root,
-                 MEM_ROOT_BLOCK_SIZE, 0, MYF(0));
-
   int error= 0;
 
   IO_CACHE *log_file= log->flip();
@@ -11578,13 +11572,9 @@ static int online_alter_read_from_binlog(THD *thd, rpl_group_info *rgi,
       break;
 
     ev->thd= thd;
-    thd->set_n_backup_active_arena(&event_arena, &backup_arena);
     error= ev->apply_event(rgi);
-    thd->restore_active_arena(&event_arena, &backup_arena);
     if (thd->is_error())
       error= 1;
-    event_arena.free_items();
-    free_root(&event_mem_root, MYF(MY_KEEP_PREALLOC));
     if (ev != rgi->rli->relay_log.description_event_for_exec)
       delete ev;
     thd_progress_report(thd, my_b_tell(log_file), thd->progress.max_counter);

sql/temporary_tables.cc

@@ -627,8 +627,7 @@ bool THD::drop_temporary_table(TABLE *table, bool *is_trans, bool delete_table)
                           table->s->db.str, table->s->table_name.str));
 
   // close all handlers in case it is statement abort and some can be left
-  if (is_error())
-    table->file->ha_reset();
+  table->file->ha_reset();
 
   locked= lock_temporary_tables();