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[原创]Oracle Redo Latch相关测试

2016-12-09

Oracle Redo latch相关测试

测试持有redo copy和allocation latch后的场景:

—-session 1

SYS@PROD1> col name format a30
SYS@PROD1> select addr,latch#,name,level# from v$latch where name like '%redo%';

ADDR         LATCH# NAME                               LEVEL#
-------- ---------- ------------------------------ ----------
2000DF34        146 redo on-disk SCN                        8
2000DF98        147 ping redo on-disk SCN                   8
2001252C        185 redo writing                            1
20012594        186 redo copy                               4
200125FC        187 redo allocation                         5
20012664        188 real redo SCN                           8
20012CD0        189 readredo stats and histogram            8
200149F0        209 readable standby metadata redo          0
	             cache

200264C0        515 KFR redo allocation latch               6

9 rows selected.

SYS@PROD1> select to_number('20012594','XXXXXXXXXX') from dual;

TO_NUMBER('20012594','XXXXXXXXXX')
----------------------------------
	                 536946068

SYS@PROD1> 
SYS@PROD1> 
SYS@PROD1> 
SYS@PROD1> oradebug setmypid
Statement processed.
SYS@PROD1> oradebug call kslgetl 536946068 1
Function returned 1
SYS@PROD1> oradebug call kslgetl 536946172 1
Function returned 1
SYS@PROD1> 

—-session 2

SYS@PROD1> delete from test01 where rownum < 10;

9 rows deleted.

SYS@PROD1> commit;

Commit complete.

SYS@PROD1> select to_number('200125FC','XXXXXXXXXX') from dual;

TO_NUMBER('200125FC','XXXXXXXXXX')
----------------------------------
	                 536946172

SYS@PROD1> delete from test01 where rownum < 10;

9 rows deleted.

SYS@PROD1> commit;

Commit complete.

SYS@PROD1> 

SYS@PROD1> select count(*) from v$latch;            ---------------------> hang住
 
select count(*) from v$latch
*
ERROR at line 1:
ORA-12152: TNS:unable to send break message

SYS@PROD1>

alert报警日志:

Tue Dec 13 15:21:48 2016
Exception [type: SIGSEGV, Address not mapped to object] [ADDR:0xC7] [PC:0xDFDCCB7, kcrfw_copy_latch_cleanup()+235] [flags: 0x0, count: 1]
Errors in file /u01/app/oracle/diag/rdbms/prod1/PROD1/trace/PROD1_ora_14934.trc  (incident=26591):
ORA-07445: exception encountered: core dump [kcrfw_copy_latch_cleanup()+235] [SIGSEGV] [ADDR:0xC7] [PC:0xDFDCCB7] [Address not mapped to object] []
ORA-07443: function kslfree not found
Incident details in: /u01/app/oracle/diag/rdbms/prod1/PROD1/incident/incdir_26591/PROD1_ora_14934_i26591.trc
Use ADRCI or Support Workbench to package the incident.
See Note 411.1 at My Oracle Support for error and packaging details.
Tue Dec 13 15:21:51 2016
Dumping diagnostic data in directory=[cdmp_20161213152151], requested by (instance=1, osid=14934), summary=[incident=26591].
Tue Dec 13 15:21:52 2016

1)oracle里面是不允许同时去持有父latch和子latch的,如果你时去持有子latch,我们会发现实例会down掉。

2)redo allocation latch 这个latch的获取是在server process将redo entry copy到redo buffer(shared private strands)中之前,需要获得该latch,以便于分配空间,用于存放redo entry.

redo allocation latch 相当多

SYS@PROD1>  select addr,name,latch#,level#,child#,hash from v$latch_children where latch# in (select latch# from v$latch where name like '%redo%'); 

ADDR     NAME                     LATCH#     LEVEL#     CHILD#       HASH
-------- -------------------- ---------- ---------- ---------- ----------
36D1EF44 redo copy                   186          4          4 4092072627
36D1EEC0 redo copy                   186          4          3 4092072627
36D1EE3C redo copy                   186          4          2 4092072627
36D1EDB8 redo copy                   186          4          1 4092072627
36D218D0 redo allocation             187          5         29  999804931
36D2186C redo allocation             187          5         28  999804931
36D21808 redo allocation             187          5         27  999804931
36D217A4 redo allocation             187          5         26  999804931
36D21740 redo allocation             187          5         25  999804931
36D216DC redo allocation             187          5         24  999804931
36D21678 redo allocation             187          5         23  999804931
36D21614 redo allocation             187          5         22  999804931
36D215B0 redo allocation             187          5         21  999804931
36D2154C redo allocation             187          5         20  999804931
36D214E8 redo allocation             187          5         19  999804931
36D21484 redo allocation             187          5         18  999804931
36D21420 redo allocation             187          5         17  999804931
36D213BC redo allocation             187          5         16  999804931
36D21358 redo allocation             187          5         15  999804931
36D212F4 redo allocation             187          5         14  999804931
36D21290 redo allocation             187          5         13  999804931
36D2122C redo allocation             187          5         12  999804931
36D211C8 redo allocation             187          5         11  999804931
36D21164 redo allocation             187          5         10  999804931
36D21100 redo allocation             187          5          9  999804931
36D2109C redo allocation             187          5          8  999804931
36D21038 redo allocation             187          5          7  999804931
36D20FD4 redo allocation             187          5          6  999804931
36D20F70 redo allocation             187          5          5  999804931
36D20F0C redo allocation             187          5          4  999804931
36D20EA8 redo allocation             187          5          3  999804931
36D20E44 redo allocation             187          5          2  999804931
36D20DE0 redo allocation             187          5          1  999804931

33 rows selected.

SYS@PROD1>

3) redo writing latch

如果该latch会持有,那么必然导致lgwr无法操作,因为当事务commit后,会触发lgwr进程将redo buffer中的脏数据写入到redo logfile中,而lgwr在写之前,必须先获得redo writing latch。

—- session 1

SYS@PROD1> col name format a30 
SYS@PROD1> select addr,latch#,name,level# from v$latch where name like '%redo%';

ADDR         LATCH# NAME                               LEVEL#
-------- ---------- ------------------------------ ----------
2000DF34        146 redo on-disk SCN                        8
2000DF98        147 ping redo on-disk SCN                   8
2001252C        185 redo writing                            1
20012594        186 redo copy                               4
200125FC        187 redo allocation                         5
20012664        188 real redo SCN                           8
20012CD0        189 readredo stats and histogram            8
200149F0        209 readable standby metadata redo          0
	             cache

200264C0        515 KFR redo allocation latch               6

9 rows selected.

SYS@PROD1> oradebug setmypid
Statement processed.
SYS@PROD1> select to_number('2001252C','XXXXXXXXXXXX') from dual;

TO_NUMBER('2001252C','XXXXXXXXXXXX')
------------------------------------
	                   536945964

SYS@PROD1> oradebug call kslgetl 536945964 1
Function returned 1
SYS@PROD1> 

—- session 2

SYS@PROD1> delete from test01 where rownum < 2;

1 row deleted.

SYS@PROD1> commit;

----> commit 之后 hang住在这里

—- session 1

SYS@PROD1> oradebug call kslfre 536945964
Function returned 0
SYS@PROD1> 

—- session 2

SYS@PROD1> commit;

Commit complete.

SYS@PROD1> 

释放掉之后redo write latch之后就可以commit了


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