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v$undostat精解

Linux操作系统 作者:gydba 时间:2015-08-27 11:09:51 0 删除 编辑
因为在上节测试大表数据插入http://space.itpub.net/9240380/viewspace-630099,所以有必要学习下v$undostat 视图


V$UNDOSTAT

V$UNDOSTAT displays a histogram of statistical data to show how well the system is working. The available statistics include undo space consumption, transaction concurrency, and length of queries executed in the instance. You can use this view to estimate the amount of undo space required for the current workload. Oracle uses this view to tune undo usage in the system. The view returns null values if the system is in manual undo management mode.

--补:此视图主要是记录undo tablespace使用情况,采用10分钟为间隔采样,最多存储7day的数据,



Each row in the view keeps statistics collected in the instance for a 10-minute interval. The rows are in descending order by the BEGIN_TIME column value. Each row belongs to the time interval marked by (BEGIN_TIME, END_TIME). Each column represents the data collected for the particular statistic in that time interval. The first row of the view contains statistics for the (partial) current time period. The view contains a total of 1008 rows, spanning a 7 day cycle.

--补:每条记录对应一个10分钟的采样数据,其中每一列是一个独立属性的具体体现



Column Datatype Description
BEGIN_TIME DATE Identifies the beginning of the time interval
END_TIME DATE Identifies the end of the time interval
UNDOTSN --采样间隔的undo tablespace标识号,如果当时有多个活动的undo tablespace,仅记录最后一个活动的标识号
NUMBER 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
--采样间隔共用多少undo blocks,用它大致可以估计出你undo tablespace的大小了
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
--采样间隔事务总数


NUMBER Identifies the total number of transactions executed within the period
MAXQUERYLEN
--采样间隔运行最少事务的时间,注意是以秒计算,用它可以评估undo_rentition是否配置合理了
NUMBER Identifies the length of the longest query (in 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.
MAXQUERYID
--采样间隔运行时间最长的sql id

VARCHAR2(13) SQL identifier of the longest running SQL statement in the period
MAXCONCURRENCY
--采样间隔并发事务的最大数
NUMBER Identifies the highest number of transactions executed concurrently within the period
UNXPSTEALCNT
--多少次尝试从其它事务想得到未过期的extents


NUMBER Number of attempts to obtain undo space by stealing unexpired extents from other transactions
UNXPBLKRELCNT
--被其它事务使用的来自于undo segements未过期的块数


NUMBER Number of unexpired blocks removed from certain undo segments so they can be used by other transactions
UNXPBLKREUCNT
--事务重用的未过期的undo block数

NUMBER Number of unexpired undo blocks reused by transactions
EXPSTEALCNT
---多少次尝试从其它undo segment得到未过期的undo block


NUMBER Number of attempts to steal expired undo blocks from other undo segments
EXPBLKRELCNT
--从其它undo segment得到的过期undo block数

NUMBER Number of expired undo blocks stolen from other undo segments
EXPBLKREUCNT
--同样undo segment中,被重用的过期undo block数


NUMBER Number of expired undo blocks reused within the same undo segments
SSOLDERRCNT
--标识发生了多少次ora-01555错误,根据它可以确认undo_rentition是否配置合理
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
--多少次向undo tablespace发出空间请求,修正行为就是添加更多的undo tablespace size
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
--采样间隔活动extents的block数
NUMBER Total number of blocks in the active extents of the undo tablespace for the instance at the sampled time in the period
UNEXPIREDBLKS
---采样间隔未过期extents的block数
NUMBER Total number of blocks in the unexpired extents of the undo tablespace for the instance at the sampled time in the period
EXPIREDBLKS
---采样间隔过期extents的block块
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
--oracle给出不同负荷下的undo_retention智能建议


System tuned value indicating the period for which undo is being retained

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