btr_cur_optimistic_insert{
...
/*检查分裂页时是否有足够的空间预留给未来记录的update*/
if (leaf && !zip_size && dict_index_is_clust(index)
&& page_get_n_recs(page) >= 2
&& dict_index_get_space_reserve()+ rec_size > max_size
&&(btr_page_get_split_rec_to_right(cursor, &dummy)
||btr_page_get_split_rec_to_left(cursor, &dummy))) {
gotofail;
}
...
}
dict_index_get_space_reserve()+ rec_size > max_size
dict_index_get_space_reserve（）=1024，即当1024+记录大小rec_size大于当前page空闲空间max_size时，乐观插入失败，进入悲观插入阶段，发生B+分裂