原创： 洪斌

问题背景

在5.6.29和5.7.11版本之前，当binlog格式设置成mixed时，创建event事件中包含sysdate函数时，会导致复制中断。

与此bug相关：

场景重现

测试版本：mysql 5.6.23重现方法：分别设置statement、mixed、row格式执行以下语句，mixed格式时会导致复制中断，其他两种格式不会造成复制中断。

DELIMITER $$DROP EVENT IF EXISTS `MIS_CUMULATIVE_REV_EVENT`$$CREATE EVENT IF NOT EXISTS `MIS_CUMULATIVE_REV_EVENT`ON SCHEDULE EVERY 3 second STARTS sysdate()ON COMPLETION PRESERVEDO BEGINDECLARE EXIT HANDLER FOR SQLEXCEPTIONSELECT CONCAT('SQL EXCEPTION - TERMINATING EVENT FOR STORED PROCEDURE CALL');END$$

statement 模式

set global binlog_format=statement;

设置5s延迟观察下starts字段时间，复制正常，主从有差异

slave2 [localhost] {msandbox} (test) > change master to MASTER_DELAY=5;

Row模式

set global binlog_format=row;

复制正常，主从有差异

start字段同样有差异，因为sysdate函数是sql实际执行时间；如果是now函数，start字段时间会是一样的。

mixed模式

set global binlog_format=mixed;

关闭延迟

mixed模式下产生的binlog日志

正常的statement 和row 模式

从这些截图可知，在mixed模式下创建event时，在同一个事务内即产生了DDL statement，也产生了额外写入mysql.event表的row事件。

对于DDL语句在任何binlog格式下，都会以statement格式记录。

mixed模式下遇到非复制安全函数会转换成row模式。例如：sysdate()返回实际执行时间而非调用时间与now函数有差异。

mysql> SELECT NOW(), SLEEP(2), NOW();+---------------------+----------+---------------------+| NOW() | SLEEP(2) | NOW() |+---------------------+----------+---------------------+| 2006-04-12 13:47:36 | 0 | 2006-04-12 13:47:36 |+---------------------+----------+---------------------+mysql> SELECT SYSDATE(), SLEEP(2), SYSDATE();+---------------------+----------+---------------------+| SYSDATE() | SLEEP(2) | SYSDATE() |+---------------------+----------+---------------------+| 2006-04-12 13:47:44 | 0 | 2006-04-12 13:47:46 |+---------------------+----------+---------------------+

问题分析

利用systemtap观察下，create event时函数调用，定位为何产生了row事件。查看源码中有哪些create_event函数

[root@10-186-21-66 ~]# stap -L 'process("/usr/local/mysql/bin/mysqld").function("create_event")'process("/usr/local/mysql-advanced-5.6.23-linux-glibc2.5-x86_64/bin/mysqld").function("create_event@/export/home/pb2/build/sb_0-14249461-1422537824.58/mysqlcom-pro-5.6.23/sql/event_db_repository.cc:660") $this:class Event_db_repository* const $thd:struct THD* $parse_data:struct Event_parse_data* $create_if_not:bool $event_already_exists:bool* $table:struct TABLE* $sp:struct sp_head* $saved_mode:sql_mode_t $mdl_savepoint:class MDL_savepointprocess("/usr/local/mysql-advanced-5.6.23-linux-glibc2.5-x86_64/bin/mysqld").function("create_event@/export/home/pb2/build/sb_0-14249461-1422537824.58/mysqlcom-pro-5.6.23/sql/event_queue.cc:200") $this:class Event_queue* const $thd:struct THD* $new_element:struct Event_queue_element* $created:bool* $__FUNCTION__:char[] constprocess("/usr/local/mysql-advanced-5.6.23-linux-glibc2.5-x86_64/bin/mysqld").function("create_event@/export/home/pb2/build/sb_0-14249461-1422537824.58/mysqlcom-pro-5.6.23/sql/events.cc:307") $thd:struct THD* $parse_data:struct Event_parse_data* $if_not_exists:bool

共有以下3处

第1处：

/** Create a new event. @param[in,out] thd THD @param[in] parse_data Event's data from parsing stage @param[in] if_not_exists Whether IF NOT EXISTS was specified In case there is an event with the same name (db) and IF NOT EXISTS is specified, an warning is put into the stack. @sa Events::drop_event for the notes about locking, pre-locking and Events DDL. @retval FALSE OK @retval TRUE Error (reported)*/boolEvents::create_event(THD *thd, Event_parse_data *parse_data, bool if_not_exists)

第2处：

/** Creates an event record in mysql.event table. Creates an event. Relies on mysql_event_fill_row which is shared with ::update_event. @pre All semantic checks must be performed outside. This function only creates a record on disk. @pre The thread handle has no open tables. @param[in,out] thd THD @param[in] parse_data Parsed event definition @param[in] create_if_not TRUE if IF NOT EXISTS clause was provided to CREATE EVENT statement @param[out] event_already_exists When method is completed successfully set to true if event already exists else set to false @retval FALSE success @retval TRUE error*/boolEvent_db_repository::create_event(THD *thd, Event_parse_data *parse_data, bool create_if_not, bool *event_already_exists)

第3处：

/** Adds an event to the queue. Compute the next execution time for an event, and if it is still active, add it to the queue. Otherwise delete it. The object is left intact in case of an error. Otherwise the queue container assumes ownership of it. @param[in] thd thread handle @param[in] new_element a new element to add to the queue @param[out] created set to TRUE if no error and the element is added to the queue, FALSE otherwise @retval TRUE an error occured. The value of created is undefined, the element was not deleted. @retval FALSE success*/boolEvent_queue::create_event(THD *thd, Event_queue_element *new_element, bool *created)

利用systemtap观察以下两个函数调用情况

probe process("/usr/local/mysql/bin/mysqld").function("create_event") {printf(">>>>>>create_event\n");print_ubacktrace();}probe process("/usr/local/mysql/bin/mysqld").function("set_current_stmt_binlog_format_row") {printf("+++++set_current_stmt_binlog_format_row\n");print_ubacktrace();}

运行stap -v event.stp，在另一个mysql终端执行创建event语句

>>>>>>create_event0x7d36b1 : _ZN6Events12create_eventEP3THDP16Event_parse_datab+0x21/0x340 [...local/mysql-advanced-5.6.23-linux-glibc2.5-x86_64/bin/mysqld]0x727984 : _Z21mysql_execute_commandP3THD+0x5804/0x6ce0 [...local/mysql-advanced-5.6.23-linux-glibc2.5-x86_64/bin/mysqld]0x729178 : _Z11mysql_parseP3THDPcjP12Parser_state+0x318/0x420 [...local/mysql-advanced-5.6.23-linux-glibc2.5-x86_64/bin/mysqld]0x72a4cb : _Z16dispatch_command19enum_server_commandP3THDPcj+0xbcb/0x28f0 [...local/mysql-advanced-5.6.23-linux-glibc2.5-x86_64/bin/mysqld]0x72c2c7 : _Z10do_commandP3THD+0xd7/0x1c0 [...local/mysql-advanced-5.6.23-linux-glibc2.5-x86_64/bin/mysqld]0x6f3ee6 : _Z24do_handle_one_connectionP3THD+0x116/0x1b0 [...local/mysql-advanced-5.6.23-linux-glibc2.5-x86_64/bin/mysqld]0x6f3fc5 : handle_one_connection+0x45/0x60 [...local/mysql-advanced-5.6.23-linux-glibc2.5-x86_64/bin/mysqld]0x9b22f6 : pfs_spawn_thread+0x126/0x140 [...local/mysql-advanced-5.6.23-linux-glibc2.5-x86_64/bin/mysqld]0x7ff7b42859d1 [/lib64/libpthread-2.12.so+0x79d1/0x219000]>>>>>>create_event0x8bae27 : _ZN19Event_db_repository12create_eventEP3THDP16Event_parse_databPb+0x17/0x2b0 [...local/mysql-advanced-5.6.23-linux-glibc2.5-x86_64/bin/mysqld]0x7d377f : _ZN6Events12create_eventEP3THDP16Event_parse_datab+0xef/0x340 [...local/mysql-advanced-5.6.23-linux-glibc2.5-x86_64/bin/mysqld]0x727984 : _Z21mysql_execute_commandP3THD+0x5804/0x6ce0 [...local/mysql-advanced-5.6.23-linux-glibc2.5-x86_64/bin/mysqld]0x729178 : _Z11mysql_parseP3THDPcjP12Parser_state+0x318/0x420 [...local/mysql-advanced-5.6.23-linux-glibc2.5-x86_64/bin/mysqld]0x72a4cb : _Z16dispatch_command19enum_server_commandP3THDPcj+0xbcb/0x28f0 [...local/mysql-advanced-5.6.23-linux-glibc2.5-x86_64/bin/mysqld]0x72c2c7 : _Z10do_commandP3THD+0xd7/0x1c0 [...local/mysql-advanced-5.6.23-linux-glibc2.5-x86_64/bin/mysqld]0x6f3ee6 : _Z24do_handle_one_connectionP3THD+0x116/0x1b0 [...local/mysql-advanced-5.6.23-linux-glibc2.5-x86_64/bin/mysqld]0x6f3fc5 : handle_one_connection+0x45/0x60 [...local/mysql-a

基本可知函数调用顺序 Event::create_event -> Event_db_repository::create_event -> decide_logging_format -> set_current_stmt_binlog_format_row_if_mixed -> Event_queue::create_event

binlog.cc decide_logging_format()

 if (lex->is_stmt_unsafe() || lex->is_stmt_row_injection()|| (flags_write_all_set & HA_BINLOG_STMT_CAPABLE) == 0){/* log in row format! */set_current_stmt_binlog_format_row_if_mixed();}

因为sysdate()是非安全函数，所以调用了set_current_stmt_binlog_format_row_if_mixed()。

问题应该出在set_current_stmt_binlog_format_row_if_mixed

[root@10-186-21-66 ~]# addr2line -e /usr/local/mysql/bin/mysqld 0x8e6556/export/home/pb2/build/sb_0-14249461-1422537824.58/mysqlcom-pro-5.6.23/sql/sql_class.h:3669

sql_class.h

inline void set_current_stmt_binlog_format_row_if_mixed(){DBUG_ENTER("set_current_stmt_binlog_format_row_if_mixed");/*This should only be called from decide_logging_format.@todo Once we have ensured this, uncomment the followingstatement, remove the big comment below that, and remove thein_sub_stmt==0 condition from the following 'if'.*//* DBUG_ASSERT(in_sub_stmt == 0); *//*If in a stored/function trigger, the caller should already have done thechange. We test in_sub_stmt to prevent introducing bugs where peoplewouldn't ensure that, and would switch to row-based mode in the middleof executing a stored function/trigger (which is too late, see alsoreset_current_stmt_binlog_format_row()); this condition will make theirtests fail and so force them to propagate thelex->binlog_row_based_if_mixed upwards to the caller.*/if ((variables.binlog_format == BINLOG_FORMAT_MIXED) &&(in_sub_stmt == 0))set_current_stmt_binlog_format_row();DBUG_VOID_RETURN;}省略部分代码inline void set_current_stmt_binlog_format_row(){DBUG_ENTER("set_current_stmt_binlog_format_row");current_stmt_binlog_format= BINLOG_FORMAT_ROW;DBUG_VOID_RETURN;}

从上述代码可以看出，此函数判断binlog格式是mixed时则调用set_current_stmt_binlog_format_row，

修复补丁中，在create_event 和update_event 函数中，在调用Event_db_repository::create_event前设置binlog格式为statement，再执行Event_db_repository::create_event时就不会产生row事件了。

@@ -308,6 +308,7 @@ Events::create_event(THD *thd, Event_parse_data *parse_data,{bool ret;bool save_binlog_row_based, event_already_exists;+ ulong save_binlog_format= thd->variables.binlog_format;DBUG_ENTER("Events::create_event");if (check_if_system_tables_error())@@ -341,10 +342,15 @@ Events::create_event(THD *thd, Event_parse_data *parse_data,*/if ((save_binlog_row_based= thd->is_current_stmt_binlog_format_row()))thd->clear_current_stmt_binlog_format_row();+ thd->variables.binlog_format= BINLOG_FORMAT_STMT;+if (lock_object_name(thd, MDL_key::EVENT,parse_data->dbname.str, parse_data->name.str))- DBUG_RETURN(TRUE);+ {+ ret= true;+ goto err;+ }/* On error conditions my_error() is called so no need to handle here */if (!(ret= db_repository->create_event(thd, parse_data, if_not_exists,@@ -399,10 +405,12 @@ Events::create_event(THD *thd, Event_parse_data *parse_data,}}}+err:/* Restore the state of binlog format */DBUG_ASSERT(!thd->is_current_stmt_binlog_format_row());if (save_binlog_row_based)thd->set_current_stmt_binlog_format_row();+ thd->variables.binlog_format= save_binlog_format;

完整补丁见：git log -p 112899f406d2f1f838a180669781a8973ef3e343

结论

1. 升级到5.6.29版本或改用row模式

2. 如果event 的dml语句中出现类似sysdate()，在mixed模式下并不会造成数据不一致，会自动转成row模式

3. 在主从环境下创建event_scheduler，slave默认是禁用状态SLAVESIDE_DISABLED。应考虑主从切换后，原主从的event_scheduler状态，避免产生意外行为，比如 new slave 写入数据。