ORACLE视图DBA_HIST_UNDOSTAT-创新互联

http://docs.oracle.com/cd/E11882_01/server.112/e40402/statviews_4069.htm

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DBA_HIST_UNDOSTAT 视图

DBA_HIST_UNDOSTAT 显示Oracle UNDO表空间的历史的统计数据直方图，实例中的这些数据包括UNDO消耗、事务一致和查询执行的时长，该视图包含V$UNDOSTAT的快照。

Column	Datatype	NULL	Description
BEGIN_TIME	DATE	NOT NULL	Identifies the beginning of the time interval
END_TIME	DATE	NOT NULL	Identifies the end of the time interval
DBID	NUMBER	NOT NULL	Database ID for the snapshot
INSTANCE_NUMBER	NUMBER	NOT NULL	Instance number for the snapshot
SNAP_ID	NUMBER	NOT NULL	Unique snapshot ID
UNDOTSN	NUMBER	NOT NULL	Represents the last active undo tablespace in the duration of time. The tablespace ID of the active undo tablespace is returned in this column. If more than one undo tablespace was active in that period, the active undo tablespace that was active at the end of the period is reported.
UNDOBLKS	NUMBER		Represents the total number of undo blocks consumed. You can use this column to obtain the consumption rate of undo blocks, and thereby estimate the size of the undo tablespace needed to handle the workload on your system.
TXNCOUNT	NUMBER		Identifies the total number of transactions executed within the period
MAXQUERYLEN	NUMBER		Identifies the length of the longest query (in number of seconds) executed in the instance during the period. You can use this statistic to estimate the proper setting of the UNDO_RETENTION initialization parameter. The length of a query is measured from the cursor open time to the last fetch/execute time of the cursor. Only the length of those cursors that have been fetched/executed during the period are reflected in the view.
MAXQUERYSQLID	VARCHAR2(13)		SQL identifier of the longest running SQL statement in the period
MAXCONCURRENCY	NUMBER		Identifies the highest number of transactions executed concurrently within the period
UNXPSTEALCNT	NUMBER		Number of attempts to obtain undo space by stealing unexpired extents from other transactions
UNXPBLKRELCNT	NUMBER		Number of unexpired blocks removed from certain undo segments so they can be used by other transactions
UNXPBLKREUCNT	NUMBER		Number of unexpired undo blocks reused by transactions
EXPSTEALCNT	NUMBER		Number of attempts to steal expired undo blocks from other undo segments
EXPBLKRELCNT	NUMBER		Number of expired undo blocks stolen from other undo segments
EXPBLKREUCNT	NUMBER		Number of expired undo blocks reused within the same undo segments
SSOLDERRCNT	NUMBER		Identifies the number of times the error ORA-01555 occurred. You can use this statistic to decide whether or not the UNDO_RETENTION initialization parameter is set properly given the size of the undo tablespace. Increasing the value of UNDO_RETENTION can reduce the occurrence of this error.
NOSPACEERRCNT	NUMBER		Identifies the number of times space was requested in the undo tablespace and there was no free space available. That is, all of the space in the undo tablespace was in use by active transactions. The corrective action is to add more space to the undo tablespace.
ACTIVEBLKS	NUMBER		Total number of blocks in the active extents of the undo tablespace for the instance at the sampled time in the period
UNEXPIREDBLKS	NUMBER		Total number of blocks in the unexpired extents of the undo tablespace for the instance at the sampled time in the period
EXPIREDBLKS	NUMBER		Total number of blocks in the expired extents of the undo tablespace for the instance at the sampled time in the period
TUNED_UNDORETENTION	NUMBER		System tuned value indicating the period for which undo is being retained

默认情况下V$UNDOSTAT中的信息每10分钟增加一条记录，V$UNDOSTAT一般仅保留576条最近的UNDO记录(相当于4天的UNDO信息，10g 之前保存1008条，相当于7天的信息量)，超过的该时间的信息则被保存在DBA_HIST_UNDOSTAT视图中。该统计仅在UNDO自动管理的模式下有效。

SQL> show parameter undo_management NAME                         TYPE        VALUE ---------------------------- ----------- ------------------------------ undo_management              string      AUTO

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