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。