mysql5.7.18 ERROR 2027 (HY000): Malformed packet问题总括

ERROR 2027 (HY000): Malformed packet问题
概要
操作过程
1、本地登录
2、远程登录
3、在mysql配置文件my.cnf将query_cache关闭
4、关于read_ rnd_ buffer_ size参数
5、参考资料
mysql 5.6.36 同样操作
后续

ERROR 2027 (HY000): Malformed packet问题 

概要

• 数据库版本：5.7.18
• 远程登录mysql，select * from table报ERROR 2027。
• 数据库IP地址：192.168.1.21。

操作过程

1、本地登录

• 本地登录mysql：

1. mysql -uroot -p -S /usr/local/mysql5711/mysql.sock

• 查看mysql版本：

1. mysql> select version();
2. +------------+
3. | version() |
4. +------------+
5. | 5.7.18-log |
6. +------------+
7. 1 row in set (0.00 sec)

• 本地查询：

1. mysql> select * from sanguoyanyi;
2. +------+--------+
3. | id | people |
4. +------+--------+
5. | 1 | guojia |
6. +------+--------+
7. 1 row in set (0.00 sec)

2、远程登录

• 远程登录并查询：

1. mysql -uroot -p -h192.168.1.21
2. root@192.168.1.21 : sbtest 09:37:38> select * from sanguoyanyi;
3. ERROR 2027 (HY000): Malformed packet

• select * 会报错，但是指定所有字段正常查询：

1. root@192.168.1.21 : sbtest 09:48:46> select id,people from sanguoyanyi;
2. +------+--------+
3. | id | people |
4. +------+--------+
5. | 1 | guojia |
6. +------+--------+
7. 1 row in set (0.00 sec)
8. root@192.168.1.21 : sbtest 09:48:56> desc sanguoyanyi;
9. +--------+-------------+------+-----+---------+-------+
10. | Field | Type | Null | Key | Default | Extra |
11. +--------+-------------+------+-----+---------+-------+
12. | id | int(11) | YES | | NULL | |
13. | people | varchar(13) | YES | | NULL | |
14. +--------+-------------+------+-----+---------+-------+
15. 2 rows in set (0.00 sec)

• 查看query_cache设置情况：

1. root@192.168.1.21 : sbtest 09:38:11> show variables like 'query_cache%';
2. +------------------------------+----------+
3. | Variable_name | Value |
4. +------------------------------+----------+
5. | query_cache_limit | 2097152 |
6. | query_cache_min_res_unit | 4096 |
7. | query_cache_size | 67108864 |
8. | query_cache_type | ON |
9. | query_cache_wlock_invalidate | OFF |
10. +------------------------------+----------+
11. 5 rows in set (0.01 sec)

• 关闭query_cache：

1. root@192.168.1.21 : sbtest 09:49:05> set global query_cache_size=0;
2. Query OK, 0 rows affected (0.00 sec)
3. root@192.168.1.21 : sbtest 09:58:37> set global query_cache_type=0;
4. Query OK, 0 rows affected (0.00 sec)
5. root@192.168.1.21 : sbtest 09:58:53> show variables like 'query_cache%%';
6. +------------------------------+---------+
7. | Variable_name | Value |
8. +------------------------------+---------+
9. | query_cache_limit | 2097152 |
10. | query_cache_min_res_unit | 4096 |
11. | query_cache_size | 0 |
12. | query_cache_type | ON |
13. | query_cache_wlock_invalidate | OFF |
14. +------------------------------+---------+
15. 5 rows in set (0.00 sec)

• 关闭qc之后再次查询，发现此时查询结果正常

1. root@192.168.1.21 : sbtest 09:58:58> select * from sanguoyanyi;
2. +------+--------+
3. | id | people |
4. +------+--------+
5. | 1 | guojia |
6. +------+--------+
7. 1 row in set (0.00 sec)

3、在mysql配置文件my.cnf将query_cache关闭

• 在配置文件里配置：

1. query_cache_size = 0
2. query_cache_type = 0

• 然后重新启动mysql，再进行远程登录mysql，然后使用select * 查询，发现没有报错。

4、关于read_ rnd_ buffer_ size参数

• 网上说造成2027的原因是read_ rnd_ buffer_ size设置的太小，导致在初始化cache的时候，发现“只能存放小于等于2个记录”，但实际上此值为16M，足够大。

1. mysql> show variables like 'read_rnd_buffer_size';
2. +----------------------+----------+
3. | Variable_name | Value |
4. +----------------------+----------+
5. | read_rnd_buffer_size | 16777216 |
6. +----------------------+----------+
7. 1 row in set (0.00 sec)

• 为了排除这个参数的影响，尝试将此值改小

1. root@192.168.1.21 : sbtest 10:03:25> set global read_rnd_buffer_size=64000;
2. Query OK, 0 rows affected (0.00 sec)
3. root@192.168.1.21 : sbtest 10:03:55> show variables like 'read_%';
4. +----------------------+----------+
5. | Variable_name | Value |
6. +----------------------+----------+
7. | read_buffer_size | 16777216 |
8. | read_only | OFF |
9. | read_rnd_buffer_size | 64000 |
10. +----------------------+----------+
11. 3 rows in set (0.01 sec)

• 改小read_ rnd_ buffer_ size 值为64k左右之后再做查询，还是查询成功：

1. root@192.168.1.21 : sbtest 10:03:59> select * from hongloumeng;
2. +------+------------+
3. | id | role |
4. +------+------------+
5. | 1 | jiabaoyu |
6. | 2 | lindaiyu |
7. | 3 | xuebaochai |
8. | 4 | wangxifeng |
9. +------+------------+
10. 4 rows in set (0.00 sec)

• 查看关于read_ rnd_ buffer_ size参数定义之后，它针对的存在sort的语句，所以在这个case里，应该和这个参数无关。
  • This variable is used for reads from MyISAM tables, and, for any storage engine, for Multi-Range Read optimization.When reading rows from a MyISAM table in sorted order following a key-sorting operation, the rows are read through this buffer to avoid disk seeks. See Section 8.2.1.15, “ORDER BY Optimization”. Setting the variable to a large value can improve ORDER BY performance by a lot. However, this is a buffer Server System Variables allocated for each client, so you should not set the global variable to a large value. Instead, change the 
    session variable only from within those clients that need to run large queries. 
    The maximum permissible setting for read_rnd_buffer_size is 2GB.

5、参考资料

http://weibo.com/p/1001603841620565999455?from=page_100505_profile&wvr=6&mod=wenzhangmod 
https://dba.stackexchange.com/questions/102567/sql-error-2027-malformed-packet 
https://www.percona.com/blog/2007/07/24/what-exactly-is-read_rnd_buffer_size/ 
https://www.percona.com/blog/2007/09/17/mysql-what-read_buffer_size-value-is-optimal/

mysql 5.6.36 同样操作

• mysql 5.6.56版本进行相同操作，并没有出现上述问题。

后续

• 认为可能这会是一个bug，所以做了一下提交： 
  http://bugs.mysql.com/86318
• 经过2017.05.23试验，发现应该是和客户端本身的版本有关。上述试验server端是5.7.18，但client端是5.6版本，猜测应该是版本不同，通信协议可能存在差异。今天client改用5.7.18版本的进行试验，发现并没有出现ERROR 2027 Malformed packet的报错；同时用5.6的client去连接server，发现有ERROR 2027的报错。