MDEV-27234 fixup with MDEV-27557

Whenever we retrieve an older version for READ COMMITTED,
it is better to release the undo page latches
so that we can freely move to the next clustered index record
without potentially violating any latching order.

Author: dr-m

storage/innobase/dict/dict0load.cc

@@ -668,6 +668,7 @@ dict_sys_tables_rec_read(
 	ut_ad(len == 6 || len == UNIV_SQL_NULL);
 	trx_id_t id = len == 6 ? trx_read_trx_id(field) : 0;
 	if (id && trx_sys.find(nullptr, id, false)) {
+		const auto savepoint = mtr->get_savepoint();
 		heap = mem_heap_create(1024);
 		dict_index_t* index = UT_LIST_GET_FIRST(
 			dict_sys.sys_tables->indexes);
@@ -677,6 +678,7 @@ dict_sys_tables_rec_read(
 		row_vers_build_for_semi_consistent_read(
 			nullptr, rec, mtr, index, &offsets, &heap,
 			heap, &old_vers, nullptr);
+		mtr->rollback_to_savepoint(savepoint);
 		rec = old_vers;
 		if (!rec) {
 			mem_heap_free(heap);
@@ -1074,6 +1076,7 @@ dict_load_column_low(
 	const trx_id_t trx_id = trx_read_trx_id(field);
 
 	if (trx_id && mtr && trx_sys.find(nullptr, trx_id, false)) {
+		const auto savepoint = mtr->get_savepoint();
 		dict_index_t* index = UT_LIST_GET_FIRST(
 			dict_sys.sys_columns->indexes);
 		rec_offs* offsets = rec_get_offsets(
@@ -1082,6 +1085,7 @@ dict_load_column_low(
 		row_vers_build_for_semi_consistent_read(
 			nullptr, rec, mtr, index, &offsets, &heap,
 			heap, &old_vers, nullptr);
+		mtr->rollback_to_savepoint(savepoint);
 		rec = old_vers;
 		if (!old_vers) {
 			return dict_load_column_none;
@@ -1618,6 +1622,7 @@ dict_load_field_low(
 	if (!trx_id) {
 		ut_ad(!rec_get_deleted_flag(rec, 0));
 	} else if (mtr && trx_sys.find(nullptr, trx_id, false)) {
+		const auto savepoint = mtr->get_savepoint();
 		dict_index_t* sys_field = UT_LIST_GET_FIRST(
 			dict_sys.sys_fields->indexes);
 		rec_offs* offsets = rec_get_offsets(
@@ -1626,6 +1631,7 @@ dict_load_field_low(
 		row_vers_build_for_semi_consistent_read(
 			nullptr, rec, mtr, sys_field, &offsets, &heap,
 			heap, &old_vers, nullptr);
+		mtr->rollback_to_savepoint(savepoint);
 		rec = old_vers;
 		if (!old_vers || rec_get_deleted_flag(rec, 0)) {
 			return dict_load_field_none;
@@ -1828,6 +1834,7 @@ dict_load_index_low(
 		ut_ad(!rec_get_deleted_flag(rec, 0));
 	} else if (!mtr) {
 	} else if (trx_sys.find(nullptr, trx_id, false)) {
+		const auto savepoint = mtr->get_savepoint();
 		dict_index_t* sys_index = UT_LIST_GET_FIRST(
 			dict_sys.sys_indexes->indexes);
 		rec_offs* offsets = rec_get_offsets(
@@ -1836,6 +1843,7 @@ dict_load_index_low(
 		row_vers_build_for_semi_consistent_read(
 			nullptr, rec, mtr, sys_index, &offsets, &heap,
 			heap, &old_vers, nullptr);
+		mtr->rollback_to_savepoint(savepoint);
 		rec = old_vers;
 		if (!old_vers || rec_get_deleted_flag(rec, 0)) {
 			return dict_load_index_none;
@@ -2700,13 +2708,15 @@ static void dict_load_foreign_cols(dict_foreign_t *foreign, trx_id_t trx_id)
 		const trx_id_t id = trx_read_trx_id(field);
 		if (!id) {
 		} else if (id != trx_id && trx_sys.find(nullptr, id, false)) {
+			const auto savepoint = mtr.get_savepoint();
 			rec_offs* offsets = rec_get_offsets(
 				rec, sys_index, nullptr, true, ULINT_UNDEFINED,
 				&heap);
 			const rec_t* old_vers;
 			row_vers_build_for_semi_consistent_read(
 				nullptr, rec, &mtr, sys_index, &offsets, &heap,
 				heap, &old_vers, nullptr);
+			mtr.rollback_to_savepoint(savepoint);
 			rec = old_vers;
 			if (!rec || rec_get_deleted_flag(rec, 0)) {
 				goto next;
@@ -2874,12 +2884,14 @@ dict_load_foreign(
 	const trx_id_t tid = trx_read_trx_id(field);
 
 	if (tid && tid != trx_id && trx_sys.find(nullptr, tid, false)) {
+		const auto savepoint = mtr.get_savepoint();
 		rec_offs* offsets = rec_get_offsets(
 			rec, sys_index, nullptr, true, ULINT_UNDEFINED, &heap);
 		const rec_t* old_vers;
 		row_vers_build_for_semi_consistent_read(
 			nullptr, rec, &mtr, sys_index, &offsets, &heap,
 			heap, &old_vers, nullptr);
+		mtr.rollback_to_savepoint(savepoint);
 		rec = old_vers;
 		if (!rec) {
 			goto not_found;