接到报故，查看mysql数据库以下参数

1、innodb_buffer_pool_size

2、max_connections

该参数定义了数据缓冲区buffer pool大小，类似于oracle的db_cache_size

mysql> show global variables like 'innodb_buffer_pool_size';

+-------------------------+-----------+

| Variable_name           | Value     |

+-------------------------+-----------+

| innodb_buffer_pool_size | 134217728 |

+-------------------------+-----------+

1 row in set (0.00 sec)

那么如何设置该参数大小呢？首先查看运行时buffer pool相关数据指标：

mysql> show global status like 'Innodb_buffer_pool_pages_data';

+-------------------------------+-------+

| Variable_name                 | Value |

+-------------------------------+-------+

| Innodb_buffer_pool_pages_data | 314   |

+-------------------------------+-------+

1 row in set (0.00 sec)

mysql> show global status like 'Innodb_buffer_pool_pages_total';

+--------------------------------+-------+

| Variable_name                  | Value |

+--------------------------------+-------+

| Innodb_buffer_pool_pages_total | 8191  |

+--------------------------------+-------+

1 row in set (0.00 sec)

mysql> show global status like 'Innodb_page_size';

+------------------+-------+

| Variable_name    | Value |

+------------------+-------+

| Innodb_page_size | 16384 |

+------------------+-------+

1 row in set (0.00 sec)

上述三项指标的含义如下：

Innodb_buffer_pool_pages_data

The number of pages in the InnoDB buffer pool containing data. The number includes both dirty and

clean pages.

Innodb_buffer_pool_pages_total

The total size of the InnoDB buffer pool, in pages.

Innodb_page_size

InnoDB page size (default 16KB). Many values are counted in pages; the page size enables them to be

easily converted to bytes

计算Innodb_buffer_pool_pages_data/Innodb_buffer_pool_pages_total*100%

当结果 > 95% 则增加 innodb_buffer_pool_size， 建议使用物理内存的 75%

当结果 < 95% 则减少 innodb_buffer_pool_size，

建议设置大小为： Innodb_buffer_pool_pages_data* Innodb_page_size * 1.05 / (1024*1024*1024)

--------------------------------------------------------------------------------------------------------------------------------------------------------

MySQL服务器的连接数并不是要达到最大的100%为好，还是要具体问题具体分析，下面就对MySQL服务器最大连接数的合理设置进行了详尽的分析，供您参考。

我们经常会遇见“MySQL: ERROR 1040: Too many connections”的情况，一种是访问量确实很高，MySQL服务器抗不住，这个时候就要考虑增加从服务器分散读压力，另外一种情况是MySQL配置文件中max_connections值过小：

mysql> show variables like 'max_connections';

+-----------------+-------+

| Variable_name | Value |

+-----------------+-------+

| max_connections | 256 |

+-----------------+-------+

这台MySQL服务器最大连接数是256，然后查询一下服务器响应的最大连接数：

mysql> show global status like 'Max_used_connections';

MySQL服务器过去的最大连接数是245，没有达到服务器连接数上限256，应该没有出现1040错误，比较理想的设置是：

Max_used_connections / max_connections * 100% ≈ 85%

最大连接数占上限连接数的85%左右，如果发现比例在10%以下，MySQL服务器连接上线就设置得过高了。

修改：

vim /etc/my.cnf

[mysqld]

datadir=/var/lib/mysql

socket=/var/lib/mysql/mysql.sock

user=mysql

# Disabling symbolic-links is recommended to prevent assorted security risks

symbolic-links=0

log_bin = binlog

binlog_format = mixed

expire_logs_days = 7

innodb_buffer_pool_size = 4096M

lower_case_table_names = 1

max_connections = 500

[mysqld_safe]

log-error=/var/log/mysqld.log

pid-file=/var/run/mysqld/mysqld.pid

这个改完后必须重启，可以通过show variables like '%innodb_buffer_pool_size%';命令看是否修改成功。