今天做了MySQL升级，从 5.1.26-rc 升级 到 5.5.15，都是从官网下载的源码包进行编译的，其中MySQL 5.5.15是由我的同事提供的
由于现有数据库采用innodb的引擎，故采用mysqldump导出备份，然后再导入备份的方式进行升级
升级大致步骤准备：
1、对现有数据库做备份
2、对现有的MySQL程序重命名(防止升级失败还能恢复)
3、对现有权限库做单独备份
4、替换现有MySQL程序
5、启动MySQL 5.5.15，导入备份
注：特别注意mysql日志提示

在升级后启动MySQL 5.5.15的过程中遇到很多提示错误，根据错误提示加以修改，很快解决问题。

a、我所安装升级的MySQL 5.5.15，编译目录选择的是/usr/local/mysql,但是我们线上的数据库程序所在目录为/usr/local/mysql5，我按照线上的进行升级，也将程序按照线上服务部署，故在启动的过程中提示如下错误：
120717 11:19:41 mysqld_safe The file /usr/local/mysql/bin/mysqld
does not exist or is not executable. Please cd to the mysql installation
directory and restart this script from there as follows:
./bin/mysqld_safe&
See http://dev.mysql.com/doc/mysql/en/mysqld-safe.html for more information

解决方法：将程序目录更改为/usr/local/mysql

b、配置文件中有[mysqld]选项段有如下选项--log-slow-queries，这个选项属于老版本的选项，根据mysql日志文件GY_ZGC_97.err错误提示加以修改:
120717 11:21:32 mysqld_safe Starting mysqld daemon with databases from /home/mysql/data
120717 11:21:32 [Warning] The syntax '--log-slow-queries' is deprecated and will be removed in a future release. Please use '--slow-query-log'/'--slow-query-log-file' instead.
120717 11:21:32 InnoDB: The InnoDB memory heap is disabled
120717 11:21:32 InnoDB: Mutexes and rw_locks use InnoDB's own implementation
120717 11:21:32 InnoDB: Compressed tables use zlib 1.2.3
120717 11:21:33 InnoDB: Initializing buffer pool, size = 1000.0M
120717 11:21:33 InnoDB: Completed initialization of buffer pool

解决方法：将配置文件中的log-slow-queries替换为slow-query-log

c、mysql启动有个选项--datadir，该选项指定的目录没有权限问题：
120717 11:21:33  InnoDB: Operating system error number 13 in a file operation.
InnoDB: The error means mysqld does not have the access rights to
InnoDB: the directory.
InnoDB: File name ./ibdata1
InnoDB: File operation call: 'create'.
InnoDB: Cannot continue operation.
120717 11:21:33 mysqld_safe mysqld from pid file /home/mysql/data/GY_ZGC_97.pid ended

解决方法：将mysql数据目录属主更改为mysql用户：chown -R mysql.mysql data

d、mysql配置文件有如下选项：default-character-set=utf8
120717 11:22:46 InnoDB: 1.1.8 started; log sequence number 0
120717 11:22:46 [ERROR] /usr/local/mysql/bin/mysqld: unknown variable 'default-character-set=utf8'
120717 11:22:46 [ERROR] Aborting

120717 11:22:46  InnoDB: Starting shutdown...
120717 11:22:47  InnoDB: Shutdown completed; log sequence number 1595675
120717 11:22:47 [Note] /usr/local/mysql/bin/mysqld: Shutdown complete

120717 11:22:47 mysqld_safe mysqld from pid file /home/mysql/data/GY_ZGC_97.pid ended

解决方法：注释掉该选项

e、mysql权限库直接用的原来的权限库，有如下错误提示：
120717 11:25:00 [ERROR] Missing system table mysql.proxies_priv; please run mysql_upgrade to create it
120717 11:25:00 [ERROR] Native table 'performance_schema'.'events_waits_current' has the wrong structure
120717 11:25:00 [ERROR] Native table 'performance_schema'.'events_waits_history' has the wrong structure
120717 11:25:00 [ERROR] Native table 'performance_schema'.'events_waits_history_long' has the wrong structure
120717 11:25:00 [ERROR] Native table 'performance_schema'.'setup_consumers' has the wrong structure
120717 11:25:00 [ERROR] Native table 'performance_schema'.'setup_instruments' has the wrong structure
120717 11:25:00 [ERROR] Native table 'performance_schema'.'setup_timers' has the wrong structure
120717 11:25:00 [ERROR] Native table 'performance_schema'.'performance_timers' has the wrong structure
120717 11:25:00 [ERROR] Native table 'performance_schema'.'threads' has the wrong structure
120717 11:25:00 [ERROR] Native table 'performance_schema'.'events_waits_summary_by_thread_by_event_name' has the wrong structure
120717 11:25:00 [ERROR] Native table 'performance_schema'.'events_waits_summary_by_instance' has the wrong structure
120717 11:25:00 [ERROR] Native table 'performance_schema'.'events_waits_summary_global_by_event_name' has the wrong structure
120717 11:25:00 [ERROR] Native table 'performance_schema'.'file_summary_by_event_name' has the wrong structure
120717 11:25:00 [ERROR] Native table 'performance_schema'.'file_summary_by_instance' has the wrong structure
120717 11:25:00 [ERROR] Native table 'performance_schema'.'mutex_instances' has the wrong structure
120717 11:25:00 [ERROR] Native table 'performance_schema'.'rwlock_instances' has the wrong structure
120717 11:25:00 [ERROR] Native table 'performance_schema'.'cond_instances' has the wrong structure
120717 11:25:00 [ERROR] Native table 'performance_schema'.'file_instances' has the wrong structure

解决方法：根据提示只需要运行bin/mysql_upgrade，类似如下命令（特别注意：本地在启动多个数据库的情况下，需要通过--sock制定要访问的数据库）

[root@245 mysql]# bin/mysql_upgrade --sock=/tmp/mysql_log.sock -p
Enter password:
Looking for 'mysql' as: ./mysql
Looking for 'mysqlcheck' as: ./mysqlcheck
Running 'mysqlcheck' with connection arguments: '--socket=/tmp/mysql_log.sock'
Running 'mysqlcheck' with connection arguments: '--socket=/tmp/mysql_log.sock'
mysql.columns_priv                                 OK
mysql.db                                           OK
mysql.event                                        OK
mysql.func                                         OK
mysql.general_log                                  OK
mysql.help_category                                OK
mysql.help_keyword                                 OK
mysql.help_relation                                OK
mysql.help_topic                                   OK
mysql.host                                         OK
mysql.ndb_binlog_index                             OK
mysql.plugin                                       OK
mysql.proc                                         OK
mysql.procs_priv                                   OK
mysql.servers                                      OK
mysql.slow_log                                     OK
mysql.tables_priv                                  OK
mysql.time_zone                                    OK
mysql.time_zone_leap_second                        OK
mysql.time_zone_name                               OK
mysql.time_zone_transition                         OK
mysql.time_zone_transition_type                    OK
mysql.user                                         OK
Running 'mysql_fix_privilege_tables'...
OK

对于MySQL升级有很多种方法，我个人选择了导入导出的方法，如果有读者对其他的方式感兴趣，可以做相关尝试。
以上是升级过程中的相关问题，做了简单总结，适合初学者。