MySQL Redo log頁內邏輯怎麼理解

很多地方可以看到mysql redo. log不是物理格式，是物理邏輯格式，這種的邏輯是頁內邏輯，但是怎麼去理解這個頁內邏輯的概念？

如果是物理格式的話，那麼內容就應該是具體的地址，以及具體的值。redo的內容不是具體的值，而是相對值，這樣就好理解了。具體可以看下redo 的內容，比如delete命令產生的redo 如下：

mysqld!page_cur_delete_rec_write_log(unsigned char*, dict_index_t const*, mtr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/page/page0cur.cc:2510)
mysqld!page_cur_delete_rec(page_cur_t*, dict_index_t const*, unsigned long const*, mtr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/page/page0cur.cc:2639)
mysqld!btr_cur_optimistic_delete_func(btr_cur_t*, unsigned long, mtr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/btr/btr0cur.cc:5184)
mysqld!row_purge_remove_clust_if_poss_low(purge_node_t*, unsigned long) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0purge.cc:178)
mysqld!row_purge_remove_clust_if_poss(purge_node_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0purge.cc:235)
mysqld!row_purge_del_mark(purge_node_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0purge.cc:687)
mysqld!row_purge_record_func(purge_node_t*, unsigned char*, que_thr_t const*, bool) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0purge.cc:1010)
mysqld!row_purge(purge_node_t*, unsigned char*, que_thr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0purge.cc:1066)
mysqld!row_purge_step(que_thr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0purge.cc:1145)
mysqld!que_thr_step(que_thr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/que/que0que.cc:1057)
mysqld!que_run_threads_low(que_thr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/que/que0que.cc:1119)
mysqld!que_run_threads(que_thr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/que/que0que.cc:1159)
mysqld!srv_task_execute() (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/srv/srv0srv.cc:2479)
mysqld!::srv_worker_thread(void *) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/srv/srv0srv.cc:2529)
libsystem_pthread.dylib!_pthread_start (Unknown Source:0)
libsystem_pthread.dylib!thread_start (Unknown Source:0)

insert也是一樣的，記錄了一些資訊，但是針對body部分，很多文章描述的是與前一個記錄的diff，但是我看程式碼上是

if (log_ptr + rec_size <= log_end) {
memcpy(log_ptr, ins_ptr, rec_size);
mlog_close(mtr, log_ptr + rec_size);

是將insert的記錄內容複製到了log上，並不是記錄的內容差異

mysqld!page_cur_insert_rec_write_log(unsigned char*, unsigned long, unsigned char*, dict_index_t*, mtr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/page/page0cur.cc:1136)
mysqld!page_cur_insert_rec_low(unsigned char*, dict_index_t*, unsigned char const*, unsigned long*, mtr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/page/page0cur.cc:1538)
mysqld!page_cur_tuple_insert(page_cur_t*, dtuple_t const*, dict_index_t*, unsigned long**, mem_block_info_t**, unsigned long, mtr_t*, bool) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/include/page0cur.ic:287)
mysqld!btr_cur_optimistic_insert(unsigned long, btr_cur_t*, unsigned long**, mem_block_info_t**, dtuple_t*, unsigned char**, big_rec_t**, unsigned long, que_thr_t*, mtr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/btr/btr0cur.cc:3246)
mysqld!row_ins_clust_index_entry_low(unsigned long, unsigned long, dict_index_t*, unsigned long, dtuple_t*, unsigned long, que_thr_t*, bool) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0ins.cc:2612)
mysqld!row_ins_clust_index_entry(dict_index_t*, dtuple_t*, que_thr_t*, unsigned long, bool) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0ins.cc:3299)
mysqld!row_ins_index_entry(dict_index_t*, dtuple_t*, que_thr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0ins.cc:3437)
mysqld!row_ins_index_entry_step(ins_node_t*, que_thr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0ins.cc:3587)
mysqld!row_ins(ins_node_t*, que_thr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0ins.cc:3725)
mysqld!row_ins_step(que_thr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0ins.cc:3861)
mysqld!row_insert_for_mysql_using_ins_graph(unsigned char const*, row_prebuilt_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0mysql.cc:1746)
mysqld!row_insert_for_mysql(unsigned char const*, row_prebuilt_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0mysql.cc:1866)
mysqld!ha_innobase::write_row(unsigned char*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/handler/ha_innodb.cc:7612)
mysqld!handler::ha_write_row(unsigned char*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/handler.cc:8093)
mysqld!write_record(THD*, TABLE*, COPY_INFO*, COPY_INFO*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/sql_insert.cc:1895)
mysqld!Sql_cmd_insert::mysql_insert(THD*, TABLE_LIST*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/sql_insert.cc:776)
mysqld!Sql_cmd_insert::execute(THD*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/sql_insert.cc:3140)
mysqld!mysql_execute_command(THD*, bool) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/sql_parse.cc:3606)
mysqld!mysql_parse(THD*, Parser_state*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/sql_parse.cc:5584)
mysqld!dispatch_command(THD*, COM_DATA const*, enum_server_command) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/sql_parse.cc:1491)

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