mysql 5.5 版本 新增了一个性能优化的引擎: PERFORMANCE_SCHEMA这个功能默认是关闭的:
需要设置参数: performance_schema  才可以启动该功能,这个参数是静态参数,只能写在my.cnf 中 不能动态修改。
先看看有什么东西吧:

mysql> use performance_schema;
Database changed
mysql> show tables ;
+----------------------------------------------+
| Tables_in_performance_schema                 |
+----------------------------------------------+
| cond_instances                               |
| events_waits_current                         |
| events_waits_history                         |
| events_waits_history_long                    |
| events_waits_summary_by_instance             |
| events_waits_summary_by_thread_by_event_name |
| events_waits_summary_global_by_event_name    |
| file_instances                               |
| file_summary_by_event_name                   |
| file_summary_by_instance                     |
| mutex_instances                              |
| performance_timers                           |
| rwlock_instances                             |
| setup_consumers                              |
| setup_instruments                            |
| setup_timers                                 |
| threads                                      |
+----------------------------------------------+
17 rows in set (0.00 sec)

这里的数据表分为几类:

1) setup table :  设置表,配置监控选项。
2) current events table : 记录当前那些thread 正在发生什么事情。
3) history table  发生的各种事件的历史记录表
4) summary table  对各种事件的统计表
5) 杂项表,乱七八糟表。

setup 表:

mysql> SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES
    -> WHERE TABLE_SCHEMA = 'performance_schema'
    -> AND TABLE_NAME LIKE 'setup%';
+-------------------+
| TABLE_NAME        |
+-------------------+
| setup_consumers   |
| setup_instruments |
| setup_timers      |
+-------------------+

setup_consumers 描述各种事件

setup_instruments 描述这个数据库下的表名以及是否开启监控。

setup_timers   描述 监控选项已经采样频率的时间间隔

这个要多说一点 目前 performance-schema  只支持 'wait'  时间的监控,代码树上 wait/ 下的函数都可以监控到。

文档上说了只有 'wait' 事件的检测,有没有其他的选项呢?

看看源代码

static row_setup_timers all_setup_timers_data[COUNT_SETUP_TIMERS]=
{
  {
    { C_STRING_WITH_LEN("wait") },
    &wait_timer
  }
};

THR_LOCK table_setup_timers::m_table_lock;

int table_setup_timers::update_row_values(TABLE *table,
                                          const unsigned char *,
                                          unsigned char *,
                                          Field **fields)
{
  Field *f;
  longlong value;

  DBUG_ASSERT(m_row);

  for (; (f= *fields) ; fields++)
  {
    if (bitmap_is_set(table->write_set, f->field_index))
    {
      switch(f->field_index)
      {
      case 0: /* NAME */
        my_error(ER_WRONG_PERFSCHEMA_USAGE, MYF(0));
        return HA_ERR_WRONG_COMMAND;
      case 1: /* TIMER_NAME */
        value= get_field_enum(f);
        if ((value >= FIRST_TIMER_NAME) && (value <= LAST_TIMER_NAME))
          *(m_row->m_timer_name_ptr)= (enum_timer_name) value;
        else
          return HA_ERR_WRONG_COMMAND;
        break;
      default:
        DBUG_ASSERT(false);
      }
    }
  }

  return 0;
}


代码里写死了,只有 'wait' 一个值,不排除以后的版本会增加新的关键字,但至少目前就只有一个啦。
并且这个表的name 字段是不允许修改的的。 下面的修改的方法里没有做任何处理,涉及到name字段的修改,直接报错。

mysql> SELECT * FROM setup_timers;
+------+------------+
| NAME | TIMER_NAME |
+------+------------+
| wait | CYCLE      |
+------+------------+

只有 timer_name 可以update 这是一个enum 字段。

性能事件表:

mysql> SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES
    -> WHERE TABLE_SCHEMA = 'performance_schema'
    -> AND TABLE_NAME LIKE '%current';
+----------------------+
| TABLE_NAME           |
+----------------------+
| events_waits_current |
+----------------------+

记录当前正在发生的等待事件,这个表是只读的表,不能update ,delete ,但是可以truncate  

具体字段是什么意思就自己去查doc 了,这里不说了。

性能历史表:

mysql> SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES
    -> WHERE TABLE_SCHEMA = 'performance_schema'
    -> AND (TABLE_NAME LIKE '%history' OR TABLE_NAME LIKE '%history_long');
+---------------------------+
| TABLE_NAME                |
+---------------------------+
| events_waits_history      |
| events_waits_history_long |
+---------------------------+

这些表与前面的性能表的结构是一致的, history 表只保留每个线程(thread) 的最近的10个事件, history_long 记录最近的10000个事件。

新事件如表,如果旧表满了,就会丢弃旧的数据,标准的先进先出(FIFO)  这俩表也是只读表,只能truncate

事件汇总表:

mysql> SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES
    -> WHERE TABLE_SCHEMA = 'performance_schema'
    -> AND TABLE_NAME LIKE '%summary%';
+----------------------------------------------+
| TABLE_NAME                                   |
+----------------------------------------------+
| events_waits_summary_by_instance             |
| events_waits_summary_by_thread_by_event_name |
| events_waits_summary_global_by_event_name    |
| file_summary_by_event_name                   |
| file_summary_by_instance                     |
+----------------------------------------------+

按照相关的标准对进行的事件统计表,

events_waits_summary_global_by_event_name     在mysql5.5.7 以前叫: EVENTS_WAITS_SUMMARY_BY_EVENT_NAME

表也是只读的,只能turcate

performance  schema  instance 表:

mysql> SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES
    -> WHERE TABLE_SCHEMA = 'performance_schema'
    -> AND TABLE_NAME LIKE '%instances';
+------------------+
| TABLE_NAME       |
+------------------+
| cond_instances   |
| file_instances   |
| mutex_instances  |
| rwlock_instances |
+------------------+

记录各种等待事件涉及到的实例  :  主要是3类:  cond  (容器? ) mutex (互斥锁) ,rwlock (读写锁)

这表是只读的。
乱七八糟表:

mysql> SELECT * FROM performance_timers;
+-------------+-----------------+------------------+----------------+
| TIMER_NAME  | TIMER_FREQUENCY | TIMER_RESOLUTION | TIMER_OVERHEAD |
+-------------+-----------------+------------------+----------------+
| CYCLE       |      2389029850 |                1 |             72 |
| NANOSECOND  |            NULL |             NULL |           NULL |
| MICROSECOND |         1000000 |                1 |            585 |
| MILLISECOND |            1035 |                1 |            738 |
| TICK        |             101 |                1 |            630 |
+-------------+-----------------+------------------+----------------+


这个表式只读表,记录了事件采样频率的设定,我们前面说的setup_timer 表的timer_name 只能区这4个中一个。

mysql> SELECT * FROM threads;
+-----------+----------------+----------------------------------------+
| THREAD_ID | PROCESSLIST_ID | NAME                                   |
+-----------+----------------+----------------------------------------+
|         0 |              0 | thread/sql/main                        |
|         1 |              0 | thread/innodb/io_handler_thread        |
|        16 |              0 | thread/sql/signal_handler              |
|        23 |              7 | thread/sql/one_connection              |
|         5 |              0 | thread/innodb/io_handler_thread        |
|        12 |              0 | thread/innodb/srv_lock_timeout_thread  |
|        22 |              6 | thread/sql/one_connection              |

这个表记录了系统里当前存在的各种线程。
下面就是 涉及到performance_schema的各个系统参数了:

mysql> SHOW VARIABLES LIKE 'perf%';
+---------------------------------------------------+---------+
| Variable_name                                     | Value   |
+---------------------------------------------------+---------+
| performance_schema                                | ON      |
| performance_schema_events_waits_history_long_size | 10000   |
| performance_schema_events_waits_history_size      | 10      |
| performance_schema_max_cond_classes               | 80      |
| performance_schema_max_cond_instances             | 1000    |
| performance_schema_max_file_classes               | 50      |
| performance_schema_max_file_handles               | 32768   |
| performance_schema_max_file_instances             | 10000   |
| performance_schema_max_mutex_classes              | 200     |
| performance_schema_max_mutex_instances            | 1000000 |
| performance_schema_max_rwlock_classes             | 30      |
| performance_schema_max_rwlock_instances           | 1000000 |
| performance_schema_max_table_handles              | 100000  |
| performance_schema_max_table_instances            | 50000   |
| performance_schema_max_thread_classes             | 50      |
| performance_schema_max_thread_instances           | 1000    |
+---------------------------------------------------+---------+
涉及到系统状态的参数:
mysql> SHOW STATUS LIKE 'perf%';
+------------------------------------------+-------+
| Variable_name                            | Value |
+------------------------------------------+-------+
| Performance_schema_cond_classes_lost     | 0     |
| Performance_schema_cond_instances_lost   | 0     |
| Performance_schema_file_classes_lost     | 0     |
| Performance_schema_file_handles_lost     | 0     |
| Performance_schema_file_instances_lost   | 0     |
| Performance_schema_locker_lost           | 0     |
| Performance_schema_mutex_classes_lost    | 0     |
| Performance_schema_mutex_instances_lost  | 0     |
| Performance_schema_rwlock_classes_lost   | 0     |
| Performance_schema_rwlock_instances_lost | 0     |
| Performance_schema_table_handles_lost    | 0     |
| Performance_schema_table_instances_lost  | 0     |
| Performance_schema_thread_classes_lost   | 0     |
| Performance_schema_thread_instances_lost | 0     |
+------------------------------------------+-------+