很多地方可以看到mysql redo. log不是物理格式，是物理逻辑格式，这种的逻辑是页内逻辑，但是怎么去理解这个页内逻辑的概念？
如果是物理格式的话，那么内容就应该是具体的地址，以及具体的值。redo的内容不是具体的值，而是相对值，这样就好理解了。具体可以看下redo 的内容，比如delete命令产生的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也是一样的，记录了一些信息，但是针对body部分，很多文章描述的是与前一个记录的diff，但是我看代码上是
if (log_ptr + rec_size <= log_end) {
memcpy(log_ptr, ins_ptr, rec_size);
mlog_close(mtr, log_ptr + rec_size);
是将insert的记录内容拷贝到了log上，并不是记录的内容差异
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)
有兴趣学习源码的加群一起学习啊 QQ： 700072075
