binlog解析出来的日志为何无法恢复？
问题来自一位群友，简单说就是用 mysqlbinlog 工具读取 binlog 欲进行恢复，却发现数据并没被恢复。先一起来看下他是怎么做恢复的。表中原来有几条数据，但不小心被清空了：<font size="1">> select * from t1;+----+
| c1 |
+----+
|1 |
|2 |
|3 |
|4 |
+----+</font>查看binlog event，有几条插入数据，最后还有一条 truncate table 的"误操作"，现在想要把表数据恢复到误删数据前的状态。<font size="1">> show binlog events in 'binlog.000003';
+---------------+------+----------------+-----------+-------------+--------------------------------------------------------------------+
| Log_name | Pos| Event_type | Server_id | End_log_pos | Info |
+---------------+------+----------------+-----------+-------------+--------------------------------------------------------------------+
| binlog.000003 | 4 | Format_desc | 3306 | 125 | Server ver: 8.0.25-15, Binlog ver: 4 |
| binlog.000003 |125 | Previous_gtids | 3306 | 196 | aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaa1:1-5 |
| binlog.000003 |196 | Gtid | 3306 | 282 | SET @@SESSION.GTID_NEXT= 'aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaa1:6'|
| binlog.000003 |282 | Query | 3306 | 358 | BEGIN |
| binlog.000003 |358 | Rows_query | 3306 | 405 | # insert into t1 select 1 |
| binlog.000003 |405 | Table_map | 3306 | 454 | table_id: 91 (yejr.t1) |
| binlog.000003 |454 | Write_rows | 3306 | 494 | table_id: 91 flags: STMT_END_F |
| binlog.000003 |494 | Xid | 3306 | 525 | COMMIT /* xid=75 */ |
| binlog.000003 |525 | Gtid | 3306 | 611 | SET @@SESSION.GTID_NEXT= 'aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaa1:7'|
| binlog.000003 |611 | Query | 3306 | 687 | BEGIN |
| binlog.000003 |687 | Rows_query | 3306 | 734 | # insert into t1 select 2 |
| binlog.000003 |734 | Table_map | 3306 | 783 | table_id: 91 (yejr.t1) |
| binlog.000003 |783 | Write_rows | 3306 | 823 | table_id: 91 flags: STMT_END_F |
| binlog.000003 |823 | Xid | 3306 | 854 | COMMIT /* xid=76 */ |
| binlog.000003 |854 | Gtid | 3306 | 940 | SET @@SESSION.GTID_NEXT= 'aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaa1:8'|
| binlog.000003 |940 | Query | 3306 | 1016 | BEGIN |
| binlog.000003 | 1016 | Rows_query | 3306 | 1063 | # insert into t1 select 3 |
| binlog.000003 | 1063 | Table_map | 3306 | 1112 | table_id: 91 (yejr.t1) |
| binlog.000003 | 1112 | Write_rows | 3306 | 1152 | table_id: 91 flags: STMT_END_F |
| binlog.000003 | 1152 | Xid | 3306 | 1183 | COMMIT /* xid=77 */ |
| binlog.000003 | 1183 | Gtid | 3306 | 1269 | SET @@SESSION.GTID_NEXT= 'aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaa1:9'|
| binlog.000003 | 1269 | Query | 3306 | 1345 | BEGIN |
| binlog.000003 | 1345 | Rows_query | 3306 | 1392 | # insert into t1 select 4 |
| binlog.000003 | 1392 | Table_map | 3306 | 1441 | table_id: 91 (yejr.t1) |
| binlog.000003 | 1441 | Write_rows | 3306 | 1481 | table_id: 91 flags: STMT_END_F |
| binlog.000003 | 1481 | Xid | 3306 | 1512 | COMMIT /* xid=78 */ |
| binlog.000003 | 1512 | Gtid | 3306 | 1596 | SET @@SESSION.GTID_NEXT= 'aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaa1:10' |
| binlog.000003 | 1596 | Query | 3306 | 1693 | use `yejr`; truncate table t1 /* xid=87 */ |
+---------------+------+----------------+-----------+-------------+--------------------------------------------------------------------+</font>
运行下面的命令想要进行恢复数据，但发现不能正确恢复：
<font size="1">$ mysqlbinlog --start-position=4 --stop-position=1512 binlog.000003 | mysql -f yejr</font>
已经指定了读取binlog的位置是从4开始，到1512截止，因为再下一个event就是"误操作"了。之后查询 yejr.t1 表数据还是空的，没有被正确恢复。
首先再次强调线上操作要非常谨慎，如果只是普通的DML操作，建议事先打开事务模式，这样万一误操作了还能执行 rollback 回滚。但如果是DDL操作，则基本上只能依赖备份或者延迟从库，所以务必再三确认是在测试环境还是线上环境，以及即将执行的命令影响如何。再回到问题本身。在执行 mysqlbinlog 解析binlog并尝试恢复时，观察新的binlog，确认没有写入新数据，说明确实没执行恢复操作。解析binlog查看，并没有类似 SET SQL_LOG_BIN=0 等忽略binlog的设置，而如果复制SQL指令执行出来手动执行，却是可以成功的。说明binlog本身没问题，是其他原因导致的。再查看 binlog event 时注意到启用了 GTID 模式，在 GTID 模式下有个特点是要求 全局唯一。除了GTID值持续递增之外，有个不容易注意的特点是，当事务GTID在已执行过的GTID集合（Executed_Gtid_Set）中的话，就不会再次被执行。假设以下几种场景：
[*]假设当前Executed_Gtid_Set集合是 1-10，如果下一个GTID是5，它在这个范围内，则无法被执行。
[*]假设当前Executed_Gtid_Set集合是 1-10, 20-30，如果下一个GTID是13，不在这个范围内，则可以被执行。
分别做个测试：# 查看当前gtid
> show master status;
+---------------+----------+--------------+------------------+----------------------------------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+---------------+----------+--------------+------------------+----------------------------------------------+
| binlog.000004 | 762 | | | aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaa1:1-15:20 |
+---------------+----------+--------------+------------------+----------------------------------------------+
# 下一个GTID在范围内，不会被执行
> set session gtid_next='aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaa1:13';
> insert into t1 select 6;
Query OK, 0 rows affected (0.00 sec) #<-- 0 rows
# 下一个GTID不在范围内，会被执行
> set session gtid_next='aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaa1:17';
> insert into t1 select 6;
Query OK, 1 row affected (0.01 sec) #<-- 1 row affected
Records: 1Duplicates: 0Warnings: 0
# 再次查看gtid
> show master status;
+---------------+----------+--------------+------------------+-------------------------------------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+---------------+----------+--------------+------------------+-------------------------------------------------+
| binlog.000004 | 1091 | | | aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaa1:1-15:17:20 |
+---------------+----------+--------------+------------------+-------------------------------------------------+验证结果确实如上所说。知道原因就好办了，查看 mysqlbinlog 的帮助文档，查看选项 --skip-gtids 的解释：--skip-gtids Do not preserve Global Transaction Identifiers; instead
make the server execute the transactions as if they were
new.它可以使得解析出来的binlog event不再保留原来的 GTID 信息，这就可以当成新的 event 被执行了。所以，如果想要从binlog恢复数据，执行mysqlbinlog时，记得加上 --skip-gtids 选项。
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