V$MYSTAT、V$SESSTAT、V$SYSSTAT、V$STATNAME

官方解释：

V$MYSTAT

V$MYSTAT contains statistics on the current session.

Column	Datatype	Description
SID	NUMBER	ID of the current session
STATISTIC#	NUMBER	Number of the statistic
VALUE	NUMBER	Value of the statistic

V$MYSTAT视图存放了当前会话的一些统计信息， 一般会用该视图查看当前会话的ID，也就是SID列；

该视图和另外三个视图有关联性：V$SESSTAT 、V$SYSSTAT、V$STATNAME

V$SESSTAT

V$SESSTAT displays user session statistics. To find the name of the statistic associated with each statistic number (STATISTIC#), query the V$STATNAME view.

Column	Datatype	Description
SID	NUMBER	Session identifier
STATISTIC#	NUMBER	Statistic number Note: Statistics numbers are not guaranteed to remain constant from one release to another. Therefore, you should rely on the statistics name rather than its number in your applications.
VALUE	NUMBER	Statistic value

该视图显示所有会话的统计

V$SYSSTAT

V$SYSSTAT displays system statistics. To find the name of the statistic associated with each statistic number (STATISTIC#), query the V$STATNAME view.

Column	Datatype	Description
STATISTIC#	NUMBER	Statistic number Note: Statistics numbers are not guaranteed to remain constant from one release to another. Therefore, you should rely on the statistics name rather than its number in your applications.
NAME	VARCHAR2(64)	Statistic name. You can get a complete listing of statistic names by querying the V$STATNAMEview.
CLASS	NUMBER	A number representing one or more statistics class. The following class numbers are additive: 1 - User 2 - Redo 4 - Enqueue 8 - Cache 16 - OS 32 - Real Application Clusters 64 - SQL 128 - Debug
VALUE	NUMBER	Statistic value
STAT_ID	NUMBER	Identifier of the statistic

该视图显示系统的一些统计

V$STATNAME

V$STATNAME displays decoded statistic names for the statistics shown in the V$SESSTAT and V$SYSSTAT tables.

On some platforms, the NAME and CLASS columns contain additional operating system-specific statistics.

Column	Datatype	Description
STATISTIC#	NUMBER	Statistic number Note: Statistics numbers are not guaranteed to remain constant from one release to another. Therefore, you should rely on the statistics name rather than its number in your applications.
NAME	VARCHAR2(64)	Statistic name
CLASS	NUMBER	A number representing one or more statistics classes. The following class numbers are additive: 1 - User 2 - Redo 4 - Enqueue 8 - Cache 16 - OS 32 - Real Application Clusters 64 - SQL 128 - Debug
STAT_ID	NUMBER	Identifier of the statistic

该视图存放了一个STATISTIC# 所对应的名称列表，上面三个视图都可以用STATISTIC# 这一列关联取出相应的名称；