PS：MySQL5.5系列成为稳定版已经有一段时间了，但据我调查了解，在生产环境中还是以5.1系列为主。在国内的大公司里，只确定金山在使用5.5了。
公司的其中几台广告统计服务器，之前的运维直接用了自带安装的MySQL5.0系列。新来的程序员写了新的广告统计程序，使用了innodb存储引擎，偶发现5.0对innodb引擎支持不怎么好，数据库并发连接数多时会出现丢连接，于是就想升级到5.5试试。因已安装了5.0，所以不想编译安装了。就直接找了一个国外编译好的5.5的yum源，直接升级，跑了一个月了，发现很稳定！就分享一下：
1、安装MySQL 5.5.x的yum源：
rpm -Uvhhttp://repo.webtatic.com/yum/centos/5/latest.rpm
2、安装MySQL客户端的支持包：
yum -y install libmysqlclient15 --enablerepo=webtatic
3、卸载MySQL老版本的软件包：
yum -y remove mysql mysql-*
4、安装MySQL 5.5的客户端和服务端：
yum -y install mysql55 mysql55-server--enablerepo=webtatic
5、启动MySQL系统服务，更新数据库：
/etc/init.d/mysqld restart
mysql_upgrade
6、附：此台服务器的my.cnf配置
skip-locking
skip-name-resolve
key_buffer = 1024M
back_log = 3000
max_allowed_packet = 4M
table_cache = 512
sort_buffer_size = 8M
read_buffer_size = 8M
myisam_sort_buffer_size = 1024M
thread_cache = 512
query_cache_size = 512M
set-variable = wait_timeout=60
thread_concurrency = 4
log-slow-queries = slow.log
long_query_time = 1
innodb_flush_log_at_trx_commit = 2
innodb_buffer_pool_size = 1024M
#innodb_locks_unsafe_for_binlog = 1
default-storage-engine = myisam
我的MY。CNF 文件如下
[root@localhost ~]# cat /etc/my.cnf
[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
#socket=/tmp/mysql.sock
user=mysql
# Disabling symbolic-links is recommended to prevent assorted security risks
#symbolic-links=0
default-storage-engine = myisam
[mysqld_safe]
log-error=/var/log/mysqld.log
Pid-file=/var/run/mysqld/mysqld.pid
skip-locking
skip-name-resolve
key_buffer = 1024M
back_log = 3000
max_allowed_packet = 4M
table_cache = 2048
sort_buffer_size = 8M
read_buffer_size = 8M
myisam_sort_buffer_size = 2024M
thread_cache = 512
query_cache_size = 512M
set-variable = wait_timeout=60
thread_concurrency = 4
log-slow-queries = slow.log
long_query_time = 1
innodb_flush_log_at_trx_commit = 2
innodb_buffer_pool_size = 1024M
#innodb_locks_unsafe_for_binlog = 1
#default-storage-engine=myisam