MySQL並行複製中，文章中提到在prepare階段中的事務是可以並行執行的，那麼這裡指的處於prepare階段的事務已經獲取了鎖，更新了資料檔案，就等commit階段的提交，更新事務狀態，釋放undo ,鎖資源，所以prepare階段的事務互相之間是不衝突的。看下程式碼中的順序，確認下是否是先獲取鎖，然後在設定prepare狀態的。

在鎖以及設定prepare的函式上設定斷點，可以看到，是先執行了設定鎖的語句，然後才進入prepare的

鎖的堆疊

mysqld!lock_rec_lock(bool, unsigned long, buf_block_t const*, unsigned long, dict_index_t*, que_thr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/lock/lock0lock.cc:2048)
mysqld!lock_clust_rec_read_check_and_lock(unsigned long, buf_block_t const*, unsigned char const*, dict_index_t*, unsigned long const*, lock_mode, unsigned long, que_thr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/lock/lock0lock.cc:6422)
mysqld!sel_set_rec_lock(btr_pcur_t*, unsigned char const*, dict_index_t*, unsigned long const*, unsigned long, unsigned long, que_thr_t*, mtr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0sel.cc:1260)
mysqld!row_search_mvcc(unsigned char*, page_cur_mode_t, row_prebuilt_t*, unsigned long, unsigned long) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0sel.cc:5530)
mysqld!ha_innobase::index_read(unsigned char*, unsigned char const*, unsigned int, ha_rkey_function) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/handler/ha_innodb.cc:8753)
mysqld!handler::index_read_map(unsigned char*, unsigned char const*, unsigned long, ha_rkey_function) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/handler.h:2818)
mysqld!handler::ha_index_read_map(unsigned char*, unsigned char const*, unsigned long, ha_rkey_function) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/handler.cc:3046)
mysqld!handler::read_range_first(st_key_range const*, st_key_range const*, bool, bool) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/handler.cc:7411)
mysqld!handler::multi_range_read_next(char**) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/handler.cc:6476)
mysqld!DsMrr_impl::dsmrr_next(char**) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/handler.cc:6868)
mysqld!ha_innobase::multi_range_read_next(char**) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/handler/ha_innodb.cc:20587)
mysqld!QUICK_RANGE_SELECT::get_next() (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/opt_range.cc:11247)
mysqld!rr_quick(READ_RECORD*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/records.cc:405)
mysqld!Sql_cmd_delete::mysql_delete(THD*, unsigned long long) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/sql_delete.cc:470)
mysqld!Sql_cmd_delete::execute(THD*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/sql_delete.cc:1400)
mysqld!mysql_execute_command(THD*, bool) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/sql_parse.cc:3616)
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)
mysqld!do_command(THD*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/sql_parse.cc:1032)
mysqld!::handle_connection(void *) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/conn_handler/connection_handler_per_thread.cc:313)

進入prepare的堆疊

 mysqld!ha_prepare_low(THD*, bool) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/handler.cc:2339)
mysqld!MYSQL_BIN_LOG::prepare(THD*, bool) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/binlog.cc:8607)
mysqld!ha_commit_trans(THD*, bool, bool) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/handler.cc:1791)
mysqld!trans_commit_stmt(THD*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/transaction.cc:465)
mysqld!mysql_execute_command(THD*, bool) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/sql_parse.cc:4995)
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)
mysqld!do_command(THD*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/sql_parse.cc:1032)
mysqld!::handle_connection(void *) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/conn_handler/connection_handler_per_thread.cc:313)
mysqld!::pfs_spawn_thread(void *) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/perfschema/pfs.cc:2197)
libsystem_pthread.dylib!_pthread_start (未知源:0)
libsystem_pthread.dylib!thread_start (未知源:0)

關於從庫並行執行的相關程式碼，在

MySQL原始碼上理解下commit_order writeset writeset_session 

中

看了程式碼能清楚的知道是怎麼排程分發事件的。