Oracle教程 2023-02-24

Oracle 视图 V$LATCH_CHILDREN 官方解释，作用，如何使用详细说明

本站中文解释

Oracle视图V$LATCH_CHILDREN是一个动态视图，可以用来查看各类Latch子进程的信息，其中包括执行中的子进程、等待状态的子进程以及正在分配资源的子进程。在系统资源出现负载不均衡时，可以从V$LATCH_CHILDREN视图中把握进程状况。

使用V$LATCH_CHILDREN视图的办法如下：

（1）查看进程的pid

查看当前系统中的所有pid，可以执行：

SELECT sid,pid FROM v$latch_children;

（2）查看进程的执行进度

查看某个进程的执行进度，可以执行：

SELECT sid,pid,percent_complete FROM v$latch_children WHERE pid=&pid;

其中&pid指的是进程的pid。

（3）查看进程是否被阻塞

查看某个进程是否被阻塞，可以执行：

SELECT sid,pid,blocking_pid FROM v$latch_children WHERE pid=&pid;

其中&pid指的是进程的pid。若blocking_pid为0，说明该进程没有被阻塞。

官方英文解释

V$LATCH_CHILDREN displays statistics about child latches.

This view includes all columns of V$LATCH plus the CHILD# column. Note that child latches have the same parent if their LATCH# columns match each other.

Column	Datatype	Description
`ADDR`	`RAW(4 \| 8)`	Address of the latch object
`LATCH#`	`NUMBER`	Latch number of the parent latch
`CHILD#`	`NUMBER`	Child latch number (unique only to each parent latch)
`LEVEL#`	`NUMBER`	Latch level
`NAME`	`VARCHAR2(64)`	Latch name
`HASH`	`NUMBER`	Latch hash
`GETS`	`NUMBER`	Number of times the latch was requested in willing-to-wait mode
`MISSES`	`NUMBER`	Number of times the latch was requested in willing-to-wait mode and the requester had to wait
`SLEEPS`	`NUMBER`	Number of times a willing-to-wait latch request resulted in a session sleeping while waiting for the latch
`IMMEDIATE_GETS`	`NUMBER`	Number of times a latch was requested in no-wait mode
`IMMEDIATE_MISSES`	`NUMBER`	Number of times a no-wait latch request did not succeed (that is, missed)
`WAITERS_WOKEN`	`NUMBER`	This column has been deprecated and is present only for compatibility with previous releases of Oracle. No data is accumulated for this column; it will always have a value of zero.
`WAITS_HOLDING_LATCH`	`NUMBER`	This column has been deprecated and is present only for compatibility with previous releases of Oracle. No data is accumulated for this column; it will always have a value of zero.
`SPIN_GETS`	`NUMBER`	Willing-to-wait latch requests which missed the first try but succeeded while spinning
`SLEEP[1 \| 2 \| 3 \| 4 \| 5 \| 6 \| 7 \| 8 \| 9 \| 10 \| 11]`	`NUMBER`	These columns have been deprecated and are present only for compatibility with previous releases of Oracle. No data is accumulated for these columns; they will always have a value of zero. As a substitute for these columns you can query the appropriate rows of the `V$EVENT_HISTOGRAM` view where the `EVENT` column has a value of `latch free` or `latch:%`.
`WAIT_TIME`	`NUMBER`	Elapsed time spent waiting for the latch (in microseconds)
`CON_ID`	`NUMBER`	The ID of the container to which the data pertains. Possible values include: `0`: This value is used for rows containing data that pertain to the entire CDB. This value is also used for rows in non-CDBs. `1`: This value is used for rows containing data that pertain to only the root n: Where n is the applicable container ID for the rows containing data

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