Thursday Mar 28, 2013

增量检查点如何更新控制文件?

有同学在 T.askmaclean.com上提问关于增量检查点更新控制文件的问题:

Know more about checkpoint

checkpoint 分成很多种 full 、file、thread、parallel query、 object 、incremental 、logfile switch

每一种checkpoint 都有其自身的特性,例如Incremental Checkpoint会要求ckpt 每3s 更新一次controlfile 但是不更新datafile header, 而FULL CHECKPOINT要求立即完成(同步的) 且会同时更新 controlfile 和 datafile header。

Incremental Checkpoint会要求ckpt 每3s 更新一次controlfile
>>我想问的时:如何查看此时控制文件中更新的SCN?除了DUMP控制文件,有没有命令查询?

我希望通过以下演示说明该问题:

SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bi
PL/SQL Release 10.2.0.5.0 - Production
CORE    10.2.0.5.0      Production
TNS for Linux: Version 10.2.0.5.0 - Production
NLSRTL Version 10.2.0.5.0 - Production

SQL> oradebug setmypid;
Statement processed.

SQL> oradebug dump controlf 4;
Statement processed.

SQL> oradebug tracefile_name ;
/s01/admin/G10R25/udump/g10r25_ora_4660.trc

另开一个窗口等待6s在做一次controlf DUMP 

SQL>  exec dbms_lock.sleep(6);
oradebug setmypid;
oradebug dump controlf 4;
oradebug tracefile_name ;

PL/SQL procedure successfully completed.

SQL> Statement processed.
SQL> Statement processed.
SQL> /s01/admin/G10R25/udump/g10r25_ora_4663.trc

比较以上获得的2个前后有6s间隔的CONTROLFILE DUMP 文件:

[oracle@vrh8 udump]$ diff /s01/admin/G10R25/udump/g10r25_ora_4660.trc /s01/admin/G10R25/udump/g10r25_ora_4663.trc
1c1
< /s01/admin/G10R25/udump/g10r25_ora_4660.trc --- > /s01/admin/G10R25/udump/g10r25_ora_4663.trc
13c13
< Unix process pid: 4660, image: oracle@vrh8.oracle.com (TNS V1-V3) --- > Unix process pid: 4663, image: oracle@vrh8.oracle.com (TNS V1-V3)
15,18c15,19
< *** ACTION NAME:() 2012-07-22 07:59:08.215
< *** MODULE NAME:(sqlplus@vrh8.oracle.com (TNS V1-V3)) 2012-07-22 07:59:08.215
< *** SERVICE NAME:(SYS$USERS) 2012-07-22 07:59:08.215
< *** SESSION ID:(159.7) 2012-07-22 07:59:08.215 --- > *** 2012-07-22 07:59:31.779
> *** ACTION NAME:() 2012-07-22 07:59:31.779
> *** MODULE NAME:(sqlplus@vrh8.oracle.com (TNS V1-V3)) 2012-07-22 07:59:31.779
> *** SERVICE NAME:(SYS$USERS) 2012-07-22 07:59:31.779
> *** SESSION ID:(159.9) 2012-07-22 07:59:31.779
96,98c97,99
< THREAD #1 - status:0x2 flags:0x0 dirty:56
< low cache rba:(0x1a.3.0) on disk rba:(0x1a.121.0)
< on disk scn: 0x0000.013fe7a8 07/22/2012 07:59:02 --- > THREAD #1 - status:0x2 flags:0x0 dirty:57
> low cache rba:(0x1a.3.0) on disk rba:(0x1a.148.0)
> on disk scn: 0x0000.013fe7c2 07/22/2012 07:59:27
100,101c101,102
< heartbeat: 789262462 mount id: 2675014163
< Flashback log tail log# 15 thread# 1 seq 229 block 274 byte 0 --- > heartbeat: 789262470 mount id: 2675014163
> Flashback log tail log# 15 thread# 1 seq 229 block 275 byte 0
2490c2491
<   V$RMAN_STATUS: recid=140734752341296, stamp=140734752341288 --- >   V$RMAN_STATUS: recid=140733792718464, stamp=140733792718456
2501c2502
<   V$RMAN_STATUS: recid=140734752341296, stamp=140734752341288 --- >   V$RMAN_STATUS: recid=140733792718464, stamp=140733792718456
2511c2512
<   V$RMAN_STATUS: recid=140734752341296, stamp=140734752341288 --- >   V$RMAN_STATUS: recid=140733792718464, stamp=140733792718456
2521c2522
<   V$RMAN_STATUS: recid=140734752341296, stamp=140734752341288 --- >   V$RMAN_STATUS: recid=140733792718464, stamp=140733792718456
2531c2532
<   V$RMAN_STATUS: recid=140734752341296, stamp=140734752341288 --- >   V$RMAN_STATUS: recid=140733792718464, stamp=140733792718456

排除部分V$RMAN_STATUS记录存在差异外,最主要的差别在于: CHECKPOINT PROGRESS RECORDS 这是因为 ckpt 每3s一次对controlfile做heartbeat 更新 CHECKPOINT PROGRESS RECORDS。

第一次 controlf dump:

***************************************************************************
CHECKPOINT PROGRESS RECORDS
***************************************************************************
(size = 8180, compat size = 8180, section max = 11, section in-use = 0,
last-recid= 0, old-recno = 0, last-recno = 0)
(extent = 1, blkno = 2, numrecs = 11)
THREAD #1 – status:0×2 flags:0×0 dirty:56
low cache rba:(0x1a.3.0) on disk rba:(0x1a.121.0)
on disk scn: 0×0000.013fe7a8 07/22/2012 07:59:02
resetlogs scn: 0×0000.01394f1a 07/19/2012 07:27:21
heartbeat: 789262462 mount id: 2675014163
Flashback log tail log# 15 thread# 1 seq 229 block 274 byte 0
THREAD #2 – status:0×0 flags:0×0 dirty:0
low cache rba:(0×0.0.0) on disk rba:(0×0.0.0)
on disk scn: 0×0000.00000000 01/01/1988 00:00:00
resetlogs scn: 0×0000.00000000 01/01/1988 00:00:00
heartbeat: 0 mount id: 0
Flashback log tail log# 0 thread# 0 seq 0 block 0 byte 0

第二次 controlf dump:

***************************************************************************
CHECKPOINT PROGRESS RECORDS
***************************************************************************
(size = 8180, compat size = 8180, section max = 11, section in-use = 0,
last-recid= 0, old-recno = 0, last-recno = 0)
(extent = 1, blkno = 2, numrecs = 11)
THREAD #1 – status:0×2 flags:0×0 dirty:57
low cache rba:(0x1a.3.0) on disk rba:(0x1a.148.0)
on disk scn: 0×0000.013fe7c2 07/22/2012 07:59:27
resetlogs scn: 0×0000.01394f1a 07/19/2012 07:27:21
heartbeat: 789262470 mount id: 2675014163
Flashback log tail log# 15 thread# 1 seq 229 block 275 byte 0
THREAD #2 – status:0×0 flags:0×0 dirty:0
low cache rba:(0×0.0.0) on disk rba:(0×0.0.0)
on disk scn: 0×0000.00000000 01/01/1988 00:00:00
resetlogs scn: 0×0000.00000000 01/01/1988 00:00:00

差异在于
on disk rba
on disk scn
heartbeat
Flashback log tail log#

即实际CKPT每3s更新heartbeat控制文件一次,更新的内容是 on disk rba、on disk scn、heartbeat 如果启用了闪回日志的话那么还有Flashback log , 而并不更新数据库当前的SCN(CURRENT SCN)。

如果你想查看ckpt每3s更新的 on disk scn的话可以参考 内部视图X$KCCCP–[K]ernel [C]ache [C]ontrolfile management [c]heckpoint [p]rogress  X$KCCCP Checkpoint Progress Records:

SQL> desc x$kcccp;
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 ADDR                                               RAW(8)
 INDX                                               NUMBER
 INST_ID                                            NUMBER
 CPTNO                                              NUMBER
 CPSTA                                              NUMBER
 CPFLG                                              NUMBER
 CPDRT                                              NUMBER
 CPRDB                                              NUMBER
 CPLRBA_SEQ                                         NUMBER
 CPLRBA_BNO                                         NUMBER
 CPLRBA_BOF                                         NUMBER
 CPODR_SEQ                                          NUMBER
 CPODR_BNO                                          NUMBER
 CPODR_BOF                                          NUMBER
 CPODS                                              VARCHAR2(16)
 CPODT                                              VARCHAR2(20)
 CPODT_I                                            NUMBER
 CPHBT                                              NUMBER
 CPRLS                                              VARCHAR2(16)
 CPRLC                                              NUMBER
 CPMID                                              NUMBER
 CPSDR_SEQ                                          NUMBER
 CPSDR_BNO                                          NUMBER
 CPSDR_ADB                                          NUMBER

其中cpods 为 ” on disk scn” ,cpodr_seq||cpodr_bno||cpodr_bof为”on disk rba”,CPHBT为heartbeat number:

SQL> select cpods "on disk scn",
  2         to_char(cpodr_seq, 'xxxxxx') || ',' ||
  3         to_char(cpodr_bno, 'xxxxxxxxx') || ',' ||
  4         to_char(cpodr_bof, 'xxxxxxxxx') "on disk rba",
  5         CPHBT "heartbeat number"
  6    from x$kcccp;

on disk scn      on disk rba                    heartbeat number
---------------- ------------------------------ ----------------
20968609              1a,      240a,         0         789263152
0                      0,         0,         0                 0
0                      0,         0,         0                 0
0                      0,         0,         0                 0
0                      0,         0,         0                 0
0                      0,         0,         0                 0
0                      0,         0,         0                 0
0                      0,         0,         0                 0

8 rows selected.

SQL> 
SQL> 
SQL> exec dbms_lock.sleep(3);

PL/SQL procedure successfully completed.

SQL> select cpods "on disk scn",
  2         to_char(cpodr_seq, 'xxxxxx') || ',' ||
  3         to_char(cpodr_bno, 'xxxxxxxxx') || ',' ||
  4         to_char(cpodr_bof, 'xxxxxxxxx') "on disk rba",
  5         CPHBT "heartbeat number"
  6    from x$kcccp;

on disk scn      on disk rba                    heartbeat number
---------------- ------------------------------ ----------------
20968613              1a,      2410,         0         789263154
0                      0,         0,         0                 0
0                      0,         0,         0                 0
0                      0,         0,         0                 0
0                      0,         0,         0                 0
0                      0,         0,         0                 0
0                      0,         0,         0                 0
0                      0,         0,         0                 0

8 rows selected.

SQL> 
SQL> exec dbms_lock.sleep(3);

PL/SQL procedure successfully completed.

SQL> select cpods "on disk scn",
  2         to_char(cpodr_seq, 'xxxxxx') || ',' ||
  3         to_char(cpodr_bno, 'xxxxxxxxx') || ',' ||
  4         to_char(cpodr_bof, 'xxxxxxxxx') "on disk rba",
  5         CPHBT "heartbeat number"
  6    from x$kcccp;

on disk scn      on disk rba                    heartbeat number
---------------- ------------------------------ ----------------
20968623              1a,      241e,         0         789263156
0                      0,         0,         0                 0
0                      0,         0,         0                 0
0                      0,         0,         0                 0
0                      0,         0,         0                 0
0                      0,         0,         0                 0
0                      0,         0,         0                 0
0                      0,         0,         0                 0

8 rows selected.
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author's avatar The Maclean Liu
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