Oracle v$session_longops 视图说明

一. 官网说明
1.1 v$session_longops
V$SESSION_LONGOPS displays the status of various operations that run for longer than 6 seconds (in absolute time). These operations currently include many backup and recovery functions, statistics gathering, and query execution, and more operations are added for every Oracle release.

To monitor query execution progress, you must be using the cost-based optimizer and you must:
（1）Set the TIMED_STATISTICS or SQL_TRACE parameters to true
（2）Gather statistics for your objects with the ANALYZE statement or the DBMS_STATS package


-- 使用条件

You can add information to this view about application-specific long-running operations by using the DBMS_APPLICATION_INFO.SET_SESSION_LONGOPS procedure.

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Column	Datatype	Description
SID	NUMBER	Identifier of the session processing the long-running operation. If multiple sessions are cooperating in the long-running operation, then SID corresponds to the main or master session.
SERIAL#	NUMBER	Serial number of the session processing the long-running operation. If multiple sessions are cooperating in the long-running operation, then SERIAL# corresponds to the main or master session. SERIAL# is 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.
OPNAME	VARCHAR2(64)	Brief description of the operation
TARGET	VARCHAR2(64)	Object on which the operation is carried out
TARGET_DESC	VARCHAR2(32)	Description of the target
SOFAR	NUMBER	Units of work done so far
TOTALWORK	NUMBER	Total units of work
UNITS	VARCHAR2(32)	Units of measurement
START_TIME	DATE	Starting time of the operation
LAST_UPDATE_TIME	DATE	Time when statistics were last updated for the operation
TIMESTAMP	DATE	Timestamp specific to the operation
TIME_REMAINING	NUMBER	Estimate (in seconds) of time remaining for the operation to complete
ELAPSED_SECONDS	NUMBER	Number of elapsed seconds from the start of the operations
CONTEXT	NUMBER	Context
MESSAGE	VARCHAR2(512)	Statistics summary message
USERNAME	VARCHAR2(30)	User ID of the user performing the operation
SQL_ADDRESS	RAW(4 | 8)	Used with the value of the SQL_HASH_VALUE column to identify the SQL statement associated with the operation
SQL_HASH_VALUE	NUMBER	Used with the value of the SQL_ADDRESS column to identify the SQL statement associated with the operation
SQL_ID	VARCHAR2(13)	SQL identifier of the SQL statement associated with the long operation, if any
SQL_PLAN_HASH_VALUE	NUMBER	SQL plan hash value; NULL if SQL_ID is NULL
SQL_EXEC_START	DATE	Time when the execution of the SQL started; NULL if SQL_ID is NULL
SQL_EXEC_ID	NUMBER	SQL execution identifier (see V$SQL_MONITOR)
SQL_PLAN_LINE_ID	NUMBER	SQL plan line ID corresponding to the long operation; NULL if the long operation is not associated with a line of the execution plan
SQL_PLAN_OPERATION	VARCHAR2(30)	Plan operation name; NULL if SQL_PLAN_LINE_ID is NULL
SQL_PLAN_OPTIONS	VARCHAR2(30)	Plan operation options; NULL if SQL_PLAN_LINE_ID is NULL
QCSID	NUMBER	Session identifier of the parallel coordinator

1.2 SQL_TRACE
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Property	Description
Parameter type	Boolean
Default value	false
Modifiable	ALTER SESSION, ALTER SYSTEM
Range of values	true | false

SQL_TRACE enables or disables the SQL trace facility. Setting this parameter to true provides information on tuning that you can use to improve performance.

Caution:
Using this initialization parameter to enable the SQL trace facility for the entire instance can have a severe performance impact. Enable the facility for specific sessions using the ALTER SESSION statement. If you must enable the facility on an entire production environment, then you can minimize performance impact by:
（1）. Maintaining at least 25% idle CPU capacity
（2）. Maintaining adequate disk space for the USER_DUMP_DEST location
（3）. Striping disk space over sufficient disks

Note:
The SQL_TRACE parameter is deprecated. Oracle recommends that you use the DBMS_MONITOR and DBMS_SESSION packages instead. SQL_TRACE is retained for backward compatibility only.
SQL_TRACE 已经被弃用了.

1.3 TIMED_STATISTICS
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Property	Description
Parameter type	Boolean
Default value	If STATISTICS_LEVEL is set to TYPICAL or ALL, then true If STATISTICS_LEVEL is set to BASIC, then false
Modifiable	ALTER SESSION, ALTER SYSTEM
Range of values	true | false

TIMED_STATISTICS specifies whether or not statistics related to time are collected.

Values:
true: The statistics are collected and stored in trace files or displayed in the V$SESSTATS and V$SYSSTATS dynamic performance views.

false: The value of all time-related statistics is set to zero. This setting lets Oracle avoid the overhead of requesting the time from the operating system.

Starting with release 11.1.0.7.0, the value of the TIMED_STATISTICS parameter cannot be set to false if the value of STATISTICS_LEVEL is set to TYPICAL or ALL.

On some systems with very fast timer access, Oracle might enable timing even if this parameter is set to false. On these systems, setting the parameter to true can sometimes produce more accurate statistics for long-running operations.


二. 相关测试

SYS@anqing2(rac2)> show parameter sql_trace
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
sql_trace boolean FALSE


SYS@anqing2(rac2)> show parameter TIMED_STATISTICS

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
timed_statistics boolean TRUE


该视图通常配合V$SESSION视图，来分析SQL运行缓慢的原因。

查询未完成操作的信息
单实例
/* Formatted on 2011/6/22 21:20:53 (QP5 v5.163.1008.3004) */
SELECT sid,
MESSAGE,
start_time,
last_update_time,
time_remaining,
elapsed_seconds
FROM V$SESSION_LONGOPS
WHERE time_remaining > 0;


RAC
/* Formatted on 2011/6/22 21:21:27 (QP5 v5.163.1008.3004) */
SELECT inst_id,
sid,
MESSAGE,
start_time,
last_update_time,
time_remaining,
elapsed_seconds
FROM GV$SESSION_LONGOPS
WHERE time_remaining > 0;






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