MySQL的非叶子节点指针是什么

本篇文章为大家展示了MySQL的非叶子节点指针是什么，内容简明扼要并且容易理解，绝对能使你眼前一亮，通过这篇文章的详细介绍希望你能有所收获。

这个指针为8字节：4（唯一定位字段个数）+4（page no）。函数为dict_index_build_node_ptr。仅此记录，后续研究

/**********************************************************************//**Builds a node pointer out of a physical record and a page number.@return own: node pointer */dtuple_t*dict_index_build_node_ptr(/*======================*/    const dict_index_t*    index,    /*!< in: index */    const rec_t*        rec,    /*!< in: record for which to build node                    pointer */    ulint            page_no,/*!< in: page number to put in node                    pointer */    mem_heap_t*        heap,    /*!< in: memory heap where pointer                    created */    ulint            level)    /*!< in: level of rec in tree:                    0 means leaf level */{    dtuple_t*    tuple;    dfield_t*    field;    byte*        buf;    ulint        n_unique;    if (dict_index_is_ibuf(index)) {        /* In a universal index tree, we take the whole record as        the node pointer if the record is on the leaf level,        on non-leaf levels we remove the last field, which        contains the page number of the child page */        ut_a(!dict_table_is_comp(index->table));        n_unique = rec_get_n_fields_old(rec);        if (level > 0) {            ut_a(n_unique > 1);            n_unique--;        }    } else {        n_unique = dict_index_get_n_unique_in_tree_nonleaf(index);// 唯一定位 到叶子节点的字段个数    }    tuple = dtuple_create(heap, n_unique + 1); //建立元组     /* When searching in the tree for the node pointer, we must not do    comparison on the last field, the page number field, as on upper    levels in the tree there may be identical node pointers with a    different page number; therefore, we set the n_fields_cmp to one    less: */    dtuple_set_n_fields_cmp(tuple, n_unique); //比较字段为 数据域    dict_index_copy_types(tuple, index, n_unique);  //进行类型复制    buf = static_cast(mem_heap_alloc(heap, 4)); //分配内存    mach_write_to_4(buf, page_no);//写入 叶子节点page no    field = dtuple_get_nth_field(tuple, n_unique);  //字段个数  能够唯一定位的字段个数    dfield_set_data(field, buf, 4);//写入字段个数    dtype_set(dfield_get_type(field), DATA_SYS_CHILD, DATA_NOT_NULL, 4);    rec_copy_prefix_to_dtuple(tuple, rec, index, n_unique, heap); //复制数据    dtuple_set_info_bits(tuple, dtuple_get_info_bits(tuple)                 | REC_STATUS_NODE_PTR);    ut_ad(dtuple_check_typed(tuple));    return(tuple);}

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