如何使用mysqldump备份

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问题描述

在一次使用mysqldump备份单表部分数据时，发现无备份数据。阵针对这一奇怪现象，进行分析。

问题复现与分析

#表结构信息mysql> show create table test.t1;+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+| Table | Create Table |+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+| t1 | CREATE TABLE `t1` (`id` int(11) NOT NULL AUTO_INCREMENT,`time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,PRIMARY KEY (`id`),KEY `idx_t` (`time`)) ENGINE=InnoDB AUTO_INCREMENT=16 DEFAULT CHARSET=utf8 |+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+1 row in set (0.00 sec)#表数据信息mysql> select * from test.t1;+----+---------------------+| id | time                |+----+---------------------+| 1 | 2018-12-10 22:15:39 || 2 | 2018-12-10 22:15:47 || 3 | 2018-12-10 22:15:50 || 4 | 2018-12-10 22:15:56 || 5 | 2018-12-10 22:15:57 || 6 | 2018-12-10 22:15:58 || 7 | 2018-12-10 22:15:58 || 8 | 2018-12-10 22:16:06 || 9 | 2018-12-10 22:16:06 || 10 | 2018-12-10 22:16:07 || 11 | 2018-12-10 22:16:08 || 12 | 2018-12-10 22:16:13 || 13 | 2018-12-10 22:16:13 || 14 | 2018-12-10 22:16:14 || 15 | 2018-12-10 22:16:15 |+----+---------------------+15 rows in set (0.00 sec)

使用mysqldump --where选项备份t1表部分数据。

#使用mysqldump根据time列条件备份mysqldump -uroot -p123456 --default-character-set=utf8 -q --master-data=2 --single-transaction --databases test --tables t1 --where "time>'2018-12-10 22:16:08'">beifen.sql#通过备份文件可以看出备份结果中并无数据。...LOCK TABLES `t1` WRITE;/*!40000 ALTER TABLE `t1` DISABLE KEYS */;/*!40000 ALTER TABLE `t1` ENABLE KEYS */;UNLOCK TABLES;...

在MySQL中使用相同条件查询，并无异常，可以查到数据。

[root@master ~]# mysql -uroot -p123456 -e "select * from test.t1 where time>'2018-12-10 22:16:08'"mysql: [Warning] Using a password on the command line interface can be insecure.+----+---------------------+| id | time                |+----+---------------------+| 12 | 2018-12-10 22:16:13 || 13 | 2018-12-10 22:16:13 || 14 | 2018-12-10 22:16:14 || 15 | 2018-12-10 22:16:15 |+----+---------------------+

尝试备份t1全表数据

mysqldump -uroot -p123456 --default-character-set=utf8 -q --master-data=2 --single-transaction --databases test --tables t1 >beifen.sql#有数据，但是仔细对照，我们可以发现时间回退了八个小时。LOCK TABLES `t1` WRITE;/*!40000 ALTER TABLE `t1` DISABLE KEYS */;INSERT INTO `t1` VALUES (1,'2018-12-10 14:15:39'),(2,'2018-12-10 14:15:47'),(3,'2018-12-10 14:15:50'),(4,'2018-12-10 14:15:56'),(5,'2018-12-10 14:15:57'),(6,'2018-12-10 14:15:58'),(7,'2018-12-10 14:15:58'),(8,'2018-12-10 14:16:06'),(9,'2018-12-10 14:16:06'),(10,'2018-12-10 14:16:07'),(11,'2018-12-10 14:16:08'),(12,'2018-12-10 14:16:13'),(13,'2018-12-10 14:16:13'),(14,'2018-12-10 14:16:14'),(15,'2018-12-10 14:16:15');/*!40000 ALTER TABLE `t1` ENABLE KEYS */;UNLOCK TABLES;#查看mysqldump备份文件头部信息，mysqldump使用的是中时区。.../*!40103 SET TIME_ZONE='+00:00' */;...#查看MySQL和系统时区。mysql> show variables like '%time%';+---------------------------------+-------------------+| Variable_name | Value |+---------------------------------+-------------------+| binlog_max_flush_queue_time | 0 || connect_timeout | 10 || datetime_format | %Y-%m-%d %H:%i:%s || default_password_lifetime | 0 || delayed_insert_timeout | 300 || explicit_defaults_for_timestamp | OFF || flush_time | 0 || have_statement_timeout | YES || innodb_flush_log_at_timeout | 1 || innodb_lock_wait_timeout | 50 || innodb_old_blocks_time | 1000 || innodb_rollback_on_timeout | OFF || interactive_timeout | 28800 || lc_time_names | en_US || lock_wait_timeout | 31536000 || log_timestamps | UTC || long_query_time | 10.000000 || max_execution_time | 0 || net_read_timeout | 30 || net_write_timeout | 60 || rpl_semi_sync_master_timeout | 10000 || rpl_stop_slave_timeout | 31536000 || slave_net_timeout | 60 || slow_launch_time | 2 || system_time_zone | CST || time_format | %H:%i:%s || time_zone | +08:00 || timestamp | 1544775697.554299 || wait_timeout | 28800 |+---------------------------------+-------------------+29 rows in set (0.01 sec)[root@master ~]# date -RWed, 12 Dec 2018 16:00:34 +0800#模拟数据恢复mysql> drop table test.t1;mysql -uroot -p123456 select * from t1;+----+---------------------+| id | time |+----+---------------------+| 1 | 2018-12-10 22:15:39 || 2 | 2018-12-10 22:15:47 || 3 | 2018-12-10 22:15:50 || 4 | 2018-12-10 22:15:56 || 5 | 2018-12-10 22:15:57 || 6 | 2018-12-10 22:15:58 || 7 | 2018-12-10 22:15:58 || 8 | 2018-12-10 22:16:06 || 9 | 2018-12-10 22:16:06 || 10 | 2018-12-10 22:16:07 || 11 | 2018-12-10 22:16:08 || 12 | 2018-12-10 22:16:13 || 13 | 2018-12-10 22:16:13 || 14 | 2018-12-10 22:16:14 || 15 | 2018-12-10 22:16:15 |+----+---------------------+15 rows in set (0.00 sec)#数据恢复正常。但是存在一个问题，因为mysqldump备份时会把数据进行时区转换，导致mysqldump过滤条件与筛选的数据差8个小时，所以可能会使where条件过滤不准确。比如文章开头所碰到的问题。

解决办法

#使用--skip-tz-utc，不使用mysqldump默认的中时区。mysqldump --default-character-set=utf8 -q --master-data=2 --single-transaction --databases test --tables t1 --where "time='2018-12-10 22:16:08'" -uroot -p123456 --skip-tz-utc>beifen.sql#数据完全正确，文件头部无时区转换，所以数据恢复时正常。LOCK TABLES `t1` WRITE;/*!40000 ALTER TABLE `t1` DISABLE KEYS */;INSERT INTO `t1` VALUES (11,'2018-12-10 22:16:08');/*!40000 ALTER TABLE `t1` ENABLE KEYS */;UNLOCK TABLES;

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