案例1：lvm机型，从库创建完成后，主库qps 2w，从库6k多。从某个时间点开始延迟在缓慢增加，一直涨到7w多秒才发现去处理；从库io的util很高
故障原因：查看配置发现这个从库开启了log_slave_updates，一直在产生binlog，当把这个参数禁用或者设置sync_binlog=0以后，util立马就降下来了，同步延迟也就慢慢变小了直到为0，此前已经发现多次使用lvm逻辑卷管理或者SSD的机器的udb只要开启了这个sync_binlog=1，好像磁盘util都很高，也没有深究为什么。
案例2：slave延迟一直在增大，从库和主库的qps很低，io都很低，从库cpu 100%
故障原因：因为从库执行SQL是单线程的，所以只能利用一个CPU的资源，当cpu使用率到100%，整个库都卡住了，不管什么操作都很慢；发现从库上只执行一个简单的主键更新操作，所以很奇怪为什么主键更新还这么慢
ID: 6933
USER: system user
HOST:
DB: gangao
COMMAND: Connect
TIME: 457156
STATE: Updating
INFO: UPDATE`STK_DAILYQUOTEFA`SET`ID`=0x3631323538393739303330,`SECUCODE`=0x3237353233,`TRADINGDAY`=‘2003-03-18 00:00:00‘,`TRADINGSTATE`=0x31,`PREVCLOSINGPRICEBA`=0x312E363238,`OPENINGPRICEBA`=0x312E36323633,`HIGHESTPRICEBA`=0x312E36333332,`LOWESTPRICEBA`=0x312E36303734,`CLOSINGPRICEBA`=0x312E363136,`ENTRYTIME`=‘2015-07-24
15:41:13‘,`UPDATETIME`=‘2015-07-24 15:41:13‘,`GROUNDTIME`=‘2015-07-24 15:41:13‘,`UPDATEID`=0x3631323538393739303330,`RESOURCEID`=0x43616C63,`RECORDID`=NULL WHERE`ID`=0x3631323538393739303330
后来发现这里的ID是0x3631323538393739303330十六机制表示的字符串
普通10进制int值时的查询计划
mysql> explain select * from gangao.STK_DAILYQUOTEFA where id = 60737669922;
+----+-------------+------------------+-------+---------------+---------+---------+-------+------+-------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+------------------+-------+---------------+---------+---------+-------+------+-------+
| 1 | SIMPLE | STK_DAILYQUOTEFA | const | PRIMARY | PRIMARY | 8 | const | 1 | |
+----+-------------+------------------+-------+---------------+---------+---------+-------+------+-------+
1 row in set (2.84 sec)
注意这里转过去其实是字符，而问题就是出在这里
mysql> select hex(‘60737669922‘);
+------------------------+
| hex(‘60737669922‘) |
+------------------------+
| 3630373337363639393232 |
+------------------------+
1 row in set (0.00 sec)
mysql> select 0x3630373337363639393232;
+--------------------------+
| 0x3630373337363639393232 |
+--------------------------+
| 60737669922 |
+--------------------------+
1 row in set (0.00 sec)
这里再解析执行计划，发现找不到该记录
mysql> explain select * from gangao.STK_DAILYQUOTEFA where id = 0x3630373337363639393232;
+----+-------------+-------+------+---------------+------+---------+------+------+-----------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+------+---------------+------+---------+------+------+-----------------------------------------------------+
| 1 | SIMPLE | NULL | NULL | NULL | NULL | NULL | NULL | NULL | Impossible WHERE noticed after reading const tables |
+----+-------------+-------+------+---------------+------+---------+------+------+-----------------------------------------------------+
1 row in set (3.10 sec)
实际上记录是存在的
mysql> select * from gangao.STK_DAILYQUOTEFA where id = 60737669922;
+-------------+----------+---------------------+--------------+--------------------+----------------+----------------+---------------+----------------+---------------------+---------------------+---------------------+-------------+------------+----------+
| ID | SECUCODE | TRADINGDAY | TRADINGSTATE | PREVCLOSINGPRICEBA | OPENINGPRICEBA | HIGHESTPRICEBA | LOWESTPRICEBA | CLOSINGPRICEBA | ENTRYTIME | UPDATETIME | GROUNDTIME | UPDATEID | RESOURCEID | RECORDID |
+-------------+----------+---------------------+--------------+--------------------+----------------+----------------+---------------+----------------+---------------------+---------------------+---------------------+-------------+------------+----------+
| 60737669922 | 20041 | 2009-06-05 00:00:00 | 1 | 33.9315 | 33.8687 | 35.8897 | 33.7851 | 35.2277 | 2015-07-13 15:40:01 | 2015-07-13 15:40:01 | 2015-07-13 15:40:01 | 60737669922 | Calc | NULL |
+-------------+----------+---------------------+--------------+--------------------+----------------+----------------+---------------+----------------+---------------------+---------------------+---------------------+-------------+------------+----------+
1 row in set (1.94 sec)
但是转成这16进制表示的字符形式就出不来结果了
mysql> select * from gangao.STK_DAILYQUOTEFA where id = 0x3630373337363639393232;
Empty set (0.40 sec)
而这个数值真正的16进制数值应该是
mysql> select hex(60737669922);
+------------------+
| hex(60737669922) |
+------------------+
| E243F4B22 |
+------------------+
1 row in set (0.00 sec)
这里需要加上0才行
mysql> select 0xE243F4B22+0;
+---------------+
| 0xE243F4B22+0 |
+---------------+
| 60737669922 |
+---------------+
1 row in set (0.00 sec)
而这时再解析
mysql> explain select * from gangao.STK_DAILYQUOTEFA where id = 0xE243F4B22+0;
+----+-------------+------------------+-------+---------------+---------+---------+-------+------+-------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+------------------+-------+---------------+---------+---------+-------+------+-------+
| 1 | SIMPLE | STK_DAILYQUOTEFA | const | PRIMARY | PRIMARY | 8 | const | 1 | |
+----+-------------+------------------+-------+---------------+---------+---------+-------+------+-------+
1 row in set (2.83 sec)
mysql> select * from gangao.STK_DAILYQUOTEFA where id = 0xE243F4B22+0;
+-------------+----------+---------------------+--------------+--------------------+----------------+----------------+---------------+----------------+---------------------+---------------------+---------------------+-------------+------------+----------+
| ID | SECUCODE | TRADINGDAY | TRADINGSTATE | PREVCLOSINGPRICEBA | OPENINGPRICEBA | HIGHESTPRICEBA | LOWESTPRICEBA | CLOSINGPRICEBA | ENTRYTIME | UPDATETIME | GROUNDTIME | UPDATEID | RESOURCEID | RECORDID |
+-------------+----------+---------------------+--------------+--------------------+----------------+----------------+---------------+----------------+---------------------+---------------------+---------------------+-------------+------------+----------+
| 60737669922 | 20041 | 2009-06-05 00:00:00 | 1 | 33.9315 | 33.8687 | 35.8897 | 33.7851 | 35.2277 | 2015-07-13 15:40:01 | 2015-07-13 15:40:01 | 2015-07-13 15:40:01 | 60737669922 | Calc | NULL |
+-------------+----------+---------------------+--------------+--------------------+----------------+----------------+---------------+----------------+---------------------+---------------------+---------------------+-------------+------------+----------+
1 row in set (4.25 sec)
所以问题就出在客户将10进制整数123456转成字符串‘123456‘的16进制形式处理了，导致了索引根本没用上，查询缓慢，甚至一直在做无用功，根本不存在这些值。
案例3：主库上只有write操作，主库的io比较低，从库io很高，主库不存在峰值。
原因分析：后来对比主从的配置，发现主库的innodb_flush_log_at_trx_commit设置为2，而从库上innodb_flush_log_at_trx_commit是1，后来将从库也调为2或者0就没问题，这个参数具体的含义不多说，下图是没调整前，主从的io对比
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