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空暇空间max_size时，乐观插入失败，进入悲观插入阶段，发生B+分裂