1.latch之latch redo allocation

1.latch之latch redo allocation

今天项目中碰到一个LATCH，如题。第一次碰到，做个小小记录。

查看相关latch命令如下：

SQL> selectevent#,name,parameter1,parameter2,parameter3 from v$event_name where  name like '%latch: redo%';

EVENT# NAME                      PARAMETER1 PARAMETER2PARAMETER3

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

  138 latch: redo writing      address    number     tries

  139 latch: redo copy         address    number     tries

   775 latch: redo allocation    address   number     tries

1     redo writing

为占用重做缓冲区内的空间，向LGWR请求写入工作的进程需要获得redo writing锁存器。

查看REDO WRITING相关

SQL> selectname,gets,MISSES,IMMEDIATE_GETS,IMMEDIATE_MISSES,WAIT_TIME from v$latch_parentwhere name = 'redo writing';

NAME                                                                  GETS

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

   MISSES IMMEDIATE_GETS IMMEDIATE_MISSES WAIT_TIME

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

redo writing                                                        576617

        1              0                0          0

2     redo copy

如果PGA内的ChangeVector复制到重做缓冲区，要拥有redo copy锁存器。通过v$latch_children视图可以了解redocopy锁存器的活动性。

如下：

SQL> selectname,gets,MISSES,IMMEDIATE_GETS,IMMEDIATE_MISSES,WAIT_TIME fromv$latch_children where name = 'redo copy';

NAME      GETS  MISSES IMMEDIATE_GETSIMMEDIATE_MISSES  WAIT_TIME

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

redo copy   2         0         98662              205          0

3     redo allocation

将Change Vector复制到重做缓冲区，在获取重做缓冲区空间过程中需要拥有redo allocation锁存器。通过v$latch_children视图可以了解redo allocation锁存器的活动性。

SQL> selectname,gets,MISSES,IMMEDIATE_GETS,IMMEDIATE_MISSES,WAIT_TIME from v$latch_childrenwhere name = 'redo allocation';

NAME   GETS    MISSES IMMEDIATE_GETSIMMEDIATE_MISSES  WAIT_TIME

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

redo allocation  159414       30          26660               48      19541

….

共53行。