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本篇文章為大家展示了MySQL的非葉子節(jié)點(diǎn)指針是什么,內(nèi)容簡(jiǎn)明扼要并且容易理解,絕對(duì)能使你眼前一亮,通過(guò)這篇文章的詳細(xì)介紹希望你能有所收獲。
這個(gè)指針為8字節(jié):4(唯一定位字段個(gè)數(shù))+4(page no)。函數(shù)為dict_index_build_node_ptr。僅此記錄,后續(xù)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 到葉子節(jié)點(diǎn)的字段個(gè)數(shù) } tuple = dtuple_create(heap, n_unique + 1); //建立元組 /* 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); //比較字段為 數(shù)據(jù)域 dict_index_copy_types(tuple, index, n_unique); //進(jìn)行類型復(fù)制 buf = static_cast<byte*>(mem_heap_alloc(heap, 4)); //分配內(nèi)存 mach_write_to_4(buf, page_no);//寫入 葉子節(jié)點(diǎn)page no field = dtuple_get_nth_field(tuple, n_unique); //字段個(gè)數(shù) 能夠唯一定位的字段個(gè)數(shù) dfield_set_data(field, buf, 4);//寫入字段個(gè)數(shù) dtype_set(dfield_get_type(field), DATA_SYS_CHILD, DATA_NOT_NULL, 4); rec_copy_prefix_to_dtuple(tuple, rec, index, n_unique, heap); //復(fù)制數(shù)據(jù) 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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