mysql慢日志的配置与查询

1.如果你只是想确认mysql加载的是哪个配置文件那你可以使用以下方法进行确认。

mysql --verbose --help | grep my.cnf

会得到类似以下的几个地址，默认是在/etc/下的my.cnf。

/etc/my.cnf  /etc/mysql/my.cnf  /usr/local/mysql/etc/my.cnf  ~/.my.cnf

2.如果你没有使用过my.cnf，那就必须手动创建一个my.cnf目录放在上一条我们看到的几个目录下面，通常/usr/local/mysql/support-files/my-default.cnf目录下会有一个默认文件，你把它拷贝到指定位置做自定义修改就ok了。

但是有的时候/usr/local/mysql/support-files没有我们想要的文件，那就只能自行添加了。

3、

1）在 /etc 新建 my.cnf 文件

sudo vim my.cnf

保存下面内容到，my.cnf文件。

# Example MySQL config file for medium systems.  
  #  
  # This is for a system with little memory (32M - 64M) where MySQL plays  
  # an important part, or systems up to 128M where MySQL is used together with  
  # other programs (such as a web server)  
  #  
  # MySQL programs look for option files in a set of  
  # locations which depend on the deployment platform.  
  # You can copy this option file to one of those  
  # locations. For information about these locations, see:  
  # http://dev.mysql.com/doc/mysql/en/option-files.html  
  #  
  # In this file, you can use all long options that a program supports.  
  # If you want to know which options a program supports, run the program  
  # with the "--help" option.  
  # The following options will be passed to all MySQL clients  
  [client]
  default-character-set=utf8
  #password   = your_password  
  port        = 3306  
  socket      = /tmp/mysql.sock   
  # Here follows entries for some specific programs  
  # The MySQL server  
  [mysqld]
  character-set-server=utf8
  init_connect='SET NAMES utf8
  port        = 3306  
  socket      = /tmp/mysql.sock  
  skip-external-locking  
  key_buffer_size = 16M  
  max_allowed_packet = 1M  
  table_open_cache = 64  
  sort_buffer_size = 512K  
  net_buffer_length = 8K  
  read_buffer_size = 256K  
  read_rnd_buffer_size = 512K  
  myisam_sort_buffer_size = 8M  
  character-set-server=utf8  
  init_connect='SET NAMES utf8' 
# Don't listen on a TCP/IP port at all. This can be a security enhancement,  
# if all processes that need to connect to mysqld run on the same host.  
# All interaction with mysqld must be made via Unix sockets or named pipes.  
# Note that using this option without enabling named pipes on Windows  
# (via the "enable-named-pipe" option) will render mysqld useless!  
#   
#skip-networking  
 
  # Replication Master Server (default)  
  # binary logging is required for replication  
  log-bin=mysql-bin  
 
    # binary logging format - mixed recommended  
    binlog_format=mixed  
 
      # required unique id between 1 and 2^32 - 1  
      # defaults to 1 if master-host is not set  
      # but will not function as a master if omitted  
      server-id   = 1  
 
    # Replication Slave (comment out master section to use this)  
    #  
    # To configure this host as a replication slave, you can choose between  
    # two methods :  
    #  
    # 1) Use the CHANGE MASTER TO command (fully described in our manual) -  
    #    the syntax is:  
    #  
    #    CHANGE MASTER TO MASTER_HOST=<host>, MASTER_PORT=<port>,  
    #    MASTER_USER=<user>, MASTER_PASSWORD=<password> ;  
    #  
    #    where you replace <host>, <user>, <password> by quoted strings and  
    #    <port> by the master's port number (3306 by default).  
    #  
    #    Example:  
    #  
    #    CHANGE MASTER TO MASTER_HOST='125.564.12.1', MASTER_PORT=3306,  
    #    MASTER_USER='joe', MASTER_PASSWORD='secret';  
    #  
    # OR  
    #  
    # 2) Set the variables below. However, in case you choose this method, then  
    #    start replication for the first time (even unsuccessfully, for example  
    #    if you mistyped the password in master-password and the slave fails to  
    #    connect), the slave will create a master.info file, and any later  
    #    change in this file to the variables' values below will be ignored and  
    #    overridden by the content of the master.info file, unless you shutdown  
    #    the slave server, delete master.info and restart the slaver server.  
    #    For that reason, you may want to leave the lines below untouched  
    #    (commented) and instead use CHANGE MASTER TO (see above)  
    #  
    # required unique id between 2 and 2^32 - 1  
    # (and different from the master)  
    # defaults to 2 if master-host is set  
    # but will not function as a slave if omitted  
    #server-id       = 2  
    #  
    # The replication master for this slave - required  
    #master-host     =   <hostname>  
    #  
    # The username the slave will use for authentication when connecting  
    # to the master - required  
    #master-user     =   <username>  
    #  
    # The password the slave will authenticate with when connecting to  
    # the master - required  
    #master-password =   <password>  
    #  
    # The port the master is listening on.  
    # optional - defaults to 3306  
    #master-port     =  <port>  
    #  
    # binary logging - not required for slaves, but recommended  
    #log-bin=mysql-bin  
 
      # Uncomment the following if you are using InnoDB tables  
      #innodb_data_home_dir = /usr/local/mysql/data  
      #innodb_data_file_path = ibdata1:10M:autoextend  
      #innodb_log_group_home_dir = /usr/local/mysql/data  
      # You can set .._buffer_pool_size up to 50 - 80 %  
      # of RAM but beware of setting memory usage too high  
      #innodb_buffer_pool_size = 16M  
      #innodb_additional_mem_pool_size = 2M  
      # Set .._log_file_size to 25 % of buffer pool size  
      #innodb_log_file_size = 5M  
      #innodb_log_buffer_size = 8M  
      #innodb_flush_log_at_trx_commit = 1  
      #innodb_lock_wait_timeout = 50  
 
        [mysqldump]  
        quick  
        max_allowed_packet = 16M  
 
          [mysql]  
          no-auto-rehash  
          # Remove the next comment character if you are not familiar with SQL  
          #safe-updates  
          default-character-set=utf8   
 
        [myisamchk]  
        key_buffer_size = 20M  
        sort_buffer_size = 20M  
        read_buffer = 2M  
        write_buffer = 2M  
 
          [mysqlhotcopy]  
          interactive-timeout

2）修改文件读写权限

sudo chmod 664 /etc/my.cnf

==================以上只是弄了个 my.conf文件出来。下面才是配置慢日志=================

查看原始状态：

慢查询日志默认为关闭状态OFF：

mysql> show variables like 'slow_query%';
+---------------------+-----------------------------------+
| Variable_name | Value |
+---------------------+-----------------------------------+
| slow_query_log | OFF |
| slow_query_log_file | /var/lib/mysql/localhost-slow.log |
+---------------------+-----------------------------------+
2 rows in set (0.01 sec)

long_query_time默认为10秒：

mysql> show variables like 'long_query_time';
+-----------------+-----------+
| Variable_name   | Value     |
+-----------------+-----------+
| long_query_time | 10.000000 |
+-----------------+-----------+
1 row in set (0.01 sec)

4、未使用索引的查询被记录到慢查询日志中。如果调优的话，建议开启这个选项。如果开启了这个参数，full index scan的sql也会被记录到慢查询日志中。

show variables like 'log_queries_not_using_indexes'

set global log_queries_not_using_indexes=1

1.使用全局变量设置

设置开启慢查询：

mysql> set global slow_query_log='ON'; 
Query OK, 0 rows affected (0.01 sec)

设置超过1秒就记录日志：

mysql> set global long_query_time=1;
Query OK, 0 rows affected (0.00 sec)

2.使用配置文件设置

修改my.cnf文件，加入相关配置：

[root@localhost ~]# vim /etc/my.cnf

slow_query_log = ON
slow_query_log_file = /var/lib/mysql/localhost-slow.log
long_query_time = 1

然后重启mysqld服务：

[root@localhost ~]# systemctl restart mysqld

查询慢查询日志

首先向慢查询日志写入数据，我设定的long_query_time是1秒，所以用sleep函数即可：

mysql> select sleep(2);
mysql> select sleep(3);
mysql> select sleep(4);