在本期中，边肖将向您介绍如何进行会话和v $会话。文章内容丰富，从专业角度进行分析和描述。希望你看完这篇文章能有所收获。
1、前言
V$session和v$process视图是数据库管理了解系统性能和分析系统原因最常用的视图，所以作为非新手DBA管理员，需要对这两个视图有充分的了解；
2、概念
首先，我们必须了解什么是会话：通俗地说，会话是沟通双方从沟通开始到沟通结束的一个语境。这个上下文是服务器端的一块内存：它记录了这次连接的客户端机器的信息，它通过了哪个应用程序，哪个用户正在登录等等。会话和连接是同时建立的，是同一事物在不同层次上的描述。简单来说，连接是客户端和服务器之间的物理通信链路，会话是用户和服务器之间的逻辑通信交互。
oracle中的用户登录oracle服务器的先决条件是该用户拥有oracle的“创建会话”权限。oracle允许同一个用户在同一个客户端上与服务器建立多个连接，这可以从Oracle的view V $ session[select * from V $ session；]。每个会话代表用户和服务器之间的交互。就像两个国家可以同时举行很多谈判，经济，环境等等。结束经济谈判不会影响环境谈判。后台进程PMON将每隔一段时间测试一次用户的连接状态。如果连接已经断开，PMON将清理现场并释放相关资源。
1.sqlplus登录到oracle
这个场景更容易理解，一个连接对应一个会话。
2.其他客户端工具登录oracle
例如：pl/sql开发人员登录到oracle。Pl/sql开发人员可以设置每个窗口是否共享同一个会话。如果要在调试窗口中调试存储过程或函数，必须将其设置为共享会话。如果设置为非共享，pl/sql developer将在每次打开操作窗口时使用初始输入的帐户和密码建立新的连接和会话。
3.IIS通过程序登录到oracle
在这种情况下，IIS实际上是登录到oracle。连接会话的建立与iis机制有关。
对于Oracle，安全会话数应为会话=(IIS进程数)*(最小池大小)
IIS进程：在IIS6.0中，采用了新的进程隔离模式来响应用户的请求。在IIS管理器中，可以设置应用程序池中进程的最大数量。对于新的WEB应用程序请求，IIS进程管理器将启动多个W3wp.exe来响应。
4.java配置连接池
当java脚本由应用程序配置时，可以配置相应的会话数量，这样当应用程序连接时，默认情况下会分配相应的会话，这些会话无论是否连接都不会被PMON清除，从而降低了数据库的开销。
3、v$session视图的说明
数据库中的所有会话都提供了对应的视图v$session，它为所有DBA提供了一个查询和管理的窗口，因此需要了解v$session的相关信息。
圆柱
数据类型
描述
解释
SADDR n
bsp;
RAW(4 | 8)
Session address
SID
NUMBER
Session identifier
通过这两个值来确定唯一的一个session
SERIAL#
NUMBER
Session serial number. Used to uniquely identify a session's objects. Guarantees that session-level commands are applied to the correct session objects if the session ends and another session begins with the same session ID.
AUDSID
NUMBER
Auditing session ID
If AUDSID=0, then it is an internally generated SYS session.
If AUDSID=UB4MAX(4294967295), then it is a direct SYS session.
PADDR
RAW(4 | 8)
Address of the process that owns the session
process address,关联v$process的addr字段
USER#
NUMBER
Oracle user identifier
同dba_users关联
USERNAME
VARCHAR2(30)
Oracle username
同dba_users
COMMAND
NUMBER
Command in progress (last statement parsed).
session正在执行的sql id，1代表create table,3代表select
You can find the command name for any value n returned in thisCOMMAND column by running this SQL query:
SELECT command_name
FROM v$sqlcommand
WHERE command_type = n;
A value of 0 in this COMMAND column means the command is not recorded in V$SESSION.
OWNERID
NUMBER
Identifier of the user who owns the migratable session; the column contents are invalid if the value is 2147483644
For operations using Parallel Slaves, interpret this value as a 4-byte value. The low-order 2 bytes represent the session number and the high-order bytes represent the instance ID of the query coordinator.
TADDR
VARCHAR2(8)
Address of the transaction state object
当前的transaction address。可以用来关联v$transaction中的addr字段
LOCKWAIT
VARCHAR2(8)
Address of the lock the session is waiting for; NULL if none
可以通过这个字段查询出当前正在等待的锁的相关信息。sid + lockwait与v$loc中的sid + kaddr相对应。
STATUS
VARCHAR2(8)
Status of the session:
用来判断session状态。Active:正执行SQL语句。inactive:等待操作。killed:被标注为杀死
ACTIVE - Session currently executing SQL
INACTIVE - Session which is inactive and either has no configured limits or has not yet exceeded the configured limits
KILLED - Session marked to be killed
CACHED - Session temporarily cached for use by Oracle*XA
SNIPED - An inactive session that has exceeded some configured limits (for example, resource limits specified for the resource manager consumer group or idle_time specified in the user's profile). Such sessions will not be allowed to become active again.
SERVER
VARCHAR2(9)
Server type:
服务类型（一般专用类型）
DEDICATED
SHARED
PSEUDO
POOLED
NONE
SCHEMA#
NUMBER
Schema user identifier
跟USER#一致
SCHEMANAME
VARCHAR2(30)
Schema user name
跟USERNAME一致
OSUSER
VARCHAR2(30)
Operating system client user name
客户端操作系统用户名
PROCESS
VARCHAR2(24)
Operating system client process ID
客户端process id
MACHINE
VARCHAR2(64)
Operating system machine name
客户端machine name
PORT
NUMBER
Client port number
客户端的端口号
TERMINAL
VARCHAR2(30)
Operating system terminal name
客户端执行的terminal name
PROGRAM
VARCHAR2(48)
Operating system program name
客户端应用程序
TYPE
VARCHAR2(10)
Session type
用户进程还是后台进程，后台进程一般不能KILL
SQL_ADDRESS
RAW(4 | 8)
Used with SQL_HASH_VALUE to identify the SQL statement that is currently being executed
SQL_HASH_VALUE
NUMBER
Used with SQL_ADDRESS to identify the SQL statement that is currently being executed
SQL_ID
VARCHAR2(13)
SQL identifier of the SQL statement that is currently being executed
当前被执行的SQL语句，跟v$sql关联
SQL_CHILD_NUMBER
NUMBER
Child number of the SQL statement that is currently being executed
SQL_EXEC_START
DATE
Time when the execution of the SQL currently executed by this session started; NULL if SQL_ID is NULL
当前sql的开始运行时间
SQL_EXEC_ID
NUMBER
SQL execution identifier; NULL if SQL_ID is NULL or if the execution of that SQL has not yet started (see V$SQL_MONITOR)
PREV_SQL_ADDR
RAW(4 | 8)
Used with PREV_HASH_VALUE to identify the last SQL statement executed
PREV_HASH_VALUE
NUMBER
Used with SQL_HASH_VALUE to identify the last SQL statement executed
PREV_SQL_ID
VARCHAR2(13)
SQL identifier of the last SQL statement executed
刚被执行的SQL语句，从v$sql查询相应的SQL语句
PREV_CHILD_NUMBER
NUMBER
Child number of the last SQL statement executed
PREV_EXEC_START
DATE
SQL execution start of the last executed SQL statement
PREV_EXEC_ID
NUMBER
SQL execution identifier of the last executed SQL statement
PLSQL_ENTRY_OBJECT_ID
NUMBER
Object ID of the top-most PL/SQL subprogram on the stack; NULL if there is no PL/SQL subprogram on the stack
PLSQL_ENTRY_SUBPROGRAM_ID
NUMBER
Subprogram ID of the top-most PL/SQL subprogram on the stack; NULL if there is no PL/SQL subprogram on the stack
PLSQL_OBJECT_ID
NUMBER
Object ID of the currently executing PL/SQL subprogram; NULL if executing SQL
PLSQL_SUBPROGRAM_ID
NUMBER
Subprogram ID of the currently executing PL/SQL object; NULL if executing SQL
MODULE
VARCHAR2(48)
Name of the currently executing module as set by calling theDBMS_APPLICATION_INFO.SET_MODULE procedure
MODULE_HASH
NUMBER
Hash value of the MODULE column
ACTIONFootref 1
VARCHAR2(32)
Name of the currently executing action as set by calling theDBMS_APPLICATION_INFO.SET_ACTION procedure
ACTION_HASH
NUMBER
Hash value of the ACTION column
CLIENT_INFO
VARCHAR2(64)
Information set by the DBMS_APPLICATION_INFO.SET_CLIENT_INFOprocedure
FIXED_TABLE_SEQUENCE
NUMBER
This contains a number that increases every time the session completes a call to the database and there has been an intervening select from a dynamic performance table. This column can be used by performance monitors to monitor statistics in the database. Each time the performance monitor looks at the database, it only needs to look at sessions that are currently active or have a higher value in this column than the highest value that the performance monitor saw the last time. All the other sessions have been idle since the last time the performance monitor looked at the database.
ROW_WAIT_OBJ#
NUMBER
Object ID for the table containing the row specified in ROW_WAIT_ROW#
ROW_WAIT_FILE#
NUMBER
Identifier for the datafile containing the row specified inROW_WAIT_ROW#. This column is valid only if the session is currently waiting for another transaction to commit and the value ofROW_WAIT_OBJ# is not -1.
ROW_WAIT_BLOCK#
NUMBER
Identifier for the block containing the row specified in ROW_WAIT_ROW#. This column is valid only if the session is currently waiting for another transaction to commit and the value of ROW_WAIT_OBJ# is not -1.
ROW_WAIT_ROW#
NUMBER
Current row being locked. This column is valid only if the session is currently waiting for another transaction to commit and the value ofROW_WAIT_OBJ# is not -1.
TOP_LEVEL_CALL#
NUMBER
Oracle top level call number
LOGON_TIME
DATE
Time of logon
LAST_CALL_ET
NUMBER
If the session STATUS is currently ACTIVE, then the value represents the elapsed time (in seconds) since the session has become active.
If the session STATUS is currently INACTIVE, then the value represents the elapsed time (in seconds) since the session has become inactive.
PDML_ENABLED
VARCHAR2(3)
This column has been replaced by the PDML_STATUS column
FAILOVER_TYPE
VARCHAR2(13)
Indicates whether and to what extent transparent application failover (TAF) is enabled for the session:
NONE - Failover is disabled for this session
SESSION - Client is able to fail over its session following a disconnect
SELECT - Client is able to fail over queries in progress as well
See Also:
Oracle Database Concepts for more information on TAF
Oracle Database Net Services Administrator's Guide for information on configuring TAF
FAILOVER_METHOD
VARCHAR2(10)
Indicates the transparent application failover method for the session:
NONE - Failover is disabled for this session
BASIC - Client itself reconnects following a disconnect
PRECONNECT - Backup instance can support all connections from every instance for which it is backed up
FAILED_OVER
VARCHAR2(3)
Indicates whether the session is running in failover mode and failover has occurred (YES) or not (NO)
RESOURCE_CONSUMER_GROUP
VARCHAR2(32)
Name of the session's current resource consumer group
PDML_STATUS
VARCHAR2(8)
If ENABLED, the session is in a PARALLEL DML enabled mode. If DISABLED,PARALLEL DML enabled mode is not supported for the session. If FORCED, the session has been altered to force PARALLEL DML.
PDDL_STATUS
VARCHAR2(8)
If ENABLED, the session is in a PARALLEL DDL enabled mode. If DISABLED,PARALLEL DDL enabled mode is not supported for the session. If FORCED, the session has been altered to force PARALLEL DDL.
PQ_STATUS
VARCHAR2(8)
If ENABLED, the session is in a PARALLEL QUERY enabled mode. IfDISABLED, PARALLEL QUERY enabled mode is not supported for the session. If FORCED, the session has been altered to force PARALLELQUERY.
CURRENT_QUEUE_DURATION
NUMBER
If queued (1), the current amount of time the session has been queued. If not currently queued, the value is 0.
CLIENT_IDENTIFIER
VARCHAR2(64)
Client identifier of the session
BLOCKING_SESSION_STATUS
VARCHAR2(11)
This column provides details on whether there is a blocking session:
VALID - there is a blocking session, and it is identified in theBLOCKING_INSTANCE and BLOCKING_SESSION columns
NO HOLDER - there is no session blocking this session
NOT IN WAIT - this session is not in a wait
UNKNOWN - the blocking session is unknown
BLOCKING_INSTANCE
NUMBER
Instance identifier of the blocking session. This column is valid only ifBLOCKING_SESSION_STATUS has the value VALID.
BLOCKING_SESSION
NUMBER
Session identifier of the blocking session. This column is valid only ifBLOCKING_SESSION_STATUS has the value VALID.
FINAL_BLOCKING_SESSION_STATUS
VARCHAR2(11)
The final blocking session is the final element in the wait chain constructed by following the sessions that are blocked by one another starting with this session. In the case of a cyclical wait chain, one of the sessions in the wait chain will be chosen as the final blocker.
This column provides details on whether there is a final blocking session:
VALID - there is a final blocking session and it is identified in theFINAL_BLOCKING_INSTANCE and FINAL_BLOCKING_SESSION columns
NO HOLDER - there is no session blocking this session
NOT IN WAIT - this session is not in a wait
UNKNOWN - the final blocking session is unknown
FINAL_BLOCKING_INSTANCE
NUMBER
Instance identifier of the final blocking session. This column is valid only ifFINAL_BLOCKING_SESSION_STATUS has the value VALID.
FINAL_BLOCKING_SESSION
NUMBER
Session identifier of the blocking session. This column is valid only ifFINAL_BLOCKING_SESSION_STATUS has the value VALID.
SEQ#
NUMBER
A number that uniquely identifies the current or last wait (incremented for each wait)
EVENT#
NUMBER
Event number
等待事件的编号跟v$session_wait关联
EVENT
VARCHAR2(64)
Resource or event for which the session is waiting
等待事件的解释跟v$session_wait关联
See Also: Appendix C, "Oracle Wait Events"
P1TEXT
VARCHAR2(64)
Description of the first wait event parameter
对应DBA_EXTENTS的FILE_ID,BLOCK_ID,BLOCKS
P1
NUMBER
First wait event parameter (in decimal)
P1RAW
RAW(8)
First wait event parameter (in hexadecimal)Foot 2
P2TEXT
VARCHAR2(64)
Description of the second wait event parameter
P2
NUMBER
Second wait event parameter (in decimal)
P2RAW
RAW(8)
Second wait event parameter (in hexadecimal)Footref 2
P3TEXT
VARCHAR2(64)
Description of the third wait event parameter
P3
NUMBER
Third wait event parameter (in decimal)
P3RAW
RAW(8)
Third wait event parameter (in hexadecimal)Footref 2
WAIT_CLASS_ID
NUMBER
Identifier of the class of the wait event
WAIT_CLASS#
NUMBER
Number of the class of the wait event
WAIT_CLASS
VARCHAR2(64)
Name of the class of the wait event
WAIT_TIME
NUMBER
If the session is currently waiting, then the value is 0. If the session is not in a wait, then the value is as follows:
> 0 - Value is the duration of the last wait in hundredths of a second
-1 - Duration of the last wait was less than a hundredth of a second
-2 - Parameter TIMED_STATISTICS was set to false
This column has been deprecated in favor of the columnsWAIT_TIME_MICRO and STATE.
SECONDS_IN_WAIT
NUMBER
If the session is currently waiting, then the value is the amount of time waited for the current wait. If the session is not in a wait, then the value is the amount of time since the start of the last wait.
This column has been deprecated in favor of the columnsWAIT_TIME_MICRO and TIME_SINCE_LAST_WAIT_MICRO.
STATE
VARCHAR2(19)
Wait state:
WAITING - Session is currently waiting
当前session处于等待
WAITED UNKNOWN TIME - Duration of the last wait is unknown; this is the value when the parameter TIMED_STATISTICS is set to false
WAITED SHORT TIME - Last wait was less than a hundredth of a second
WAITED KNOWN TIME - Duration of the last wait is specified in theWAIT_TIME column
WAIT_TIME_MICRO
NUMBER
Amount of time waited (in microseconds). If the session is currently waiting, then the value is the time spent in the current wait. If the session is currently not in a wait, then the value is the amount of time waited in the last wait.
TIME_REMAINING_MICRO
NUMBER
Value is interpreted as follows:
> 0 - Amount of time remaining for the current wait (in microseconds)
0 - Current wait has timed out
-1 - Session can indefinitely wait in the current wait
NULL - Session is not currently waiting
TIME_SINCE_LAST_WAIT_MICRO
NUMBER
Time elapsed since the end of the last wait (in microseconds). If the session is currently in a wait, then the value is 0.
SERVICE_NAME
VARCHAR2(64)
Service name of the session
SQL_TRACE
VARCHAR2(8)
Indicates whether SQL tracing is enabled (ENABLED) or disabled (DISABLED)
是否打开跟踪
SQL_TRACE_WAITS
VARCHAR2(5)
Indicates whether wait tracing is enabled (TRUE) or not (FALSE)
SQL_TRACE_BINDS
VARCHAR2(5)
Indicates whether bind tracing is enabled (TRUE) or not (FALSE)
SQL_TRACE_PLAN_STATS
VARCHAR2(10)
Frequency at which row source statistics are dumped in the trace files for each cursor:
never
first_execution
all_executions
SESSION_EDITION_ID
NUMBER
Shows the value that, in the session, would be reported bysys_context('USERENV', 'SESSION_EDITION_ID')
CREATOR_ADDR
RAW(4 | 8)
Address of the creating process or circuit
CREATOR_SERIAL#
NUMBER
Serial number of the creating process or circuit
ECID
VARCHAR2(64)
Execution context identifier (sent by Application Server)
以上只是标注了常用的字段的注释，如果漏掉的也请各位高手补充，后续随着工作的深入也会相应的补充；
4、v$session在实际工作中的作用
4.1查询锁住对象的会话信息：
SELECT OBJECT_NAME, MACHINE, S.SID, S.SERIAL#
FROM GV$LOCKED_OBJECT L, DBA_OBJECTS O, GV$SESSION S
WHERE L.OBJECT_ID = O.OBJECT_ID AND L.SESSION_ID = S.SID;
4.2查看当前会话所执行的语句以及会话相关信息：
SELECT A.SID, A.SERIAL#, A.USERNAME, A.TERMINAL, A.PROGRAM, S.SQL_TEXT
FROM V$SESSION A, V$SQLAREA S WHERE A.SQL_ADDRESS = S.ADDRESS(+)
AND A.SQL_HASH_VALUE = S.HASH_VALUE(+) ORDER BY A.USERNAME, A.SID;
4.3杀掉会话：
ALTER SYSTEM KILL SESSION 'SID, #SERIAL'; （需要注意当前的session tpye不能是background)
上述就是小编为大家分享的如何进行session和v$session说明了，如果刚好有类似的疑惑，不妨参照上述分析进行理解。如果想知道更多相关知识，欢迎关注行业资讯频道。
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