【遇到问题】v$session_longops视图

V$seesion_longops 视图 中记录了长时间（运行时间超过 6 秒的）运行的事物，一般很多情况是全表扫描操作。

V$SESSION_LONGOPS 列说明

SID ：Session标识
SERIAL#：Session串号
OPNAME：操作简要说明
TARGET：操作运行所在的对象
TARGET_DESC：目标对象说明
SOFAR：至今为止完成的工作量
TOTALWORK：总工作量
UNITS：工作量单位
START_TIME：操作开始时间
LAST_UPDATE_TIME：统计项最后更新时间
TIME_REMAINING：预计完成操作的剩余时间(秒)
ELAPSED_SECONDS：从操作开始总花费时间(秒)
CONTEXT：前后关系
MESSAGE：统计项的完整描述
USERNAME：执行操作的用户ID
SQL_ADDRESS：用于连接查询的列
SQL_HASH_VALUE：用于连接查询的列

本系统查询如下：

1. 查询v$seesion_longops视图，发现23点时有个session执行时间为27秒

select sid,serial#,target ,last_update_time,SQL_HASH_VALUE from v$session_longops order by last_update_time;

SID    SERIAL# TARGET LAST_UPDATE_TIME SQL_HASH_VALUE

-------------------------------------------------------------------

39       2038 ITSM.ITSM_INCIDENT 2011/10/26 23:30     1640565597

2. 通过v$sqltext视图查出该sql语句

SQL> select sql_text from v$sqltext where hash_value='1640565597' order by piece;

SQL_TEXT

----------------------------------------------------------------

SELECT /*+NESTED_TABLE_GET_REFS+*/ "ITSM"."ITSM_INCIDENT".* FROM

 "ITSM"."ITSM_INCIDENT"

3. 查metalink:

This hint specifies that nested tables should be retrieved as refs.It is used for exporting, importing and loading. It should never be issued by-LO(r[:XCO^s0user queries, and in fact is unlikely to make a difference if tried.
‑mE)i#c A,y5B
W0ITPUB 个人空间 2KzT] F?[1]Ij[:I t This is also consistent with seeing large amounts of queries with this hint, and that those queries are not reused. If this is a problem for you, try to export at another time of day. If the exports are really long-running or the system load is constant, try to find out what you are using exports for and suggest alternatives (eg. backup and recovery purposes, etc). If this is a DSS system, you probably have a smaller shared pool and use import/export heavily. If so, it might be a good idea to use a bigger shared pool when doing this activity.

该hint用于expimp的嵌套表，想起该库每天晚上23点半要自动exp备份。

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