[20190312]關於增量檢查點的疑問(補充).txt

--//有人問我以前寫一個帖子的問題,關於增量檢查點的問題,連結如下:http://blog.itpub.net/267265/viewspace-2136817/

--//實際上我自己看以前寫的帖子一下子有點蒙,主要出現low_rba16=0xffffffff.ffffffff.ffff,為什麼恢復的起點是on_disk_rba16.

--//先簡單說明一下:

--//oracle現在寫髒塊基本採用增量檢查點,即使日誌切換,實際上執行也是增量檢查點,除非執行alter system checkpoint,或者

--//shutdown immediate(normal)正常關閉資料庫,如果異常關閉資料庫,啟動時執行崩潰恢復(crash recovery),恢復起點從low_rba.

--//先驗證這樣的情況:

1.環境:

SCOTT@book> @ ver1

PORT_STRING VERSION BANNER

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

x86_64/Linux 2.4.xx 11.2.0.4.0 Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production

--//寫一個指令碼check.sql,以前寫的太複雜,簡單一點:

--// x$kccrt 記錄全檢查點

--// x$kcccp 記錄增量檢查點

$ cat check.sql

column "full checkpoint_rba" format a21

column low_rba format a20

column low_rba16 format a20

column on_disk_rba format a20

column on_disk_rba16 format a20

column rtckp_rba format a20

column diff_date format 9999999.99

rem column CPOSD_ono_disk_rba_scn format 99999999999999999999999999999999

column cpdrt heading "檢查點佇列|髒塊數量|CPDRT"

column cpodt_on_disk_rba heading "檢查點佇列|on disk rba|時間戳|CPODT"

column cpods heading "檢查點佇列|on disk rba scn|CPODS"

column cphbt heading "檢查點心跳|CPHBT"

column current_sysdate heading "當前時間|SYSDATE"

set num 12

SELECT b.cplrba_seq || '.' || b.cplrba_bno || '.' || b.cplrba_bof "low_rba"

,b.cpodr_seq || '.' || b.cpodr_bno || '.' || b.cpodr_bof "on_disk_rba"

,b.CPODS "on_disk_rba_scn(CPODS)"

,TO_DATE (b.CPODT, 'MM-DD-YYYY HH24:MI:SS') "on_disk_rba_time(CPODT)"

,a.rtckp_rba_seq || '.' || a.rtckp_rba_bno || '.' || a.rtckp_rba_bof

"full checkpoint_rba"

,a.rtckp_scn "full_checkpoint(rtckp_scn)"

,TO_DATE (a.rtckp_tim, 'MM-DD-YYYY HH24:MI:SS')

"full_checkpoint_time_rtckp_tim"

,b.CPODS - a.rtckp_scn "diff_scn(on_disk_rdb-ch_scn)"

,a.rtcln "current_group"

,sysdate current_sysdate

,CPDRT

FROM x$kccrt a, x$kcccp b

WHERE a.rtnum = b.cptno AND A.INST_ID = b.inst_id;

2.測試:

SYS@book> shutdown abort ;

ORACLE instance shut down.

SYS@book> startup mount

ORACLE instance started.

Total System Global Area 643084288 bytes

Fixed Size 2255872 bytes

Variable Size 205521920 bytes

Database Buffers 427819008 bytes

Redo Buffers 7487488 bytes

Database mounted.

SYS@book> archive log list

Database log mode Archive Mode

Automatic archival Enabled

Archive destination /u01/app/oracle/archivelog/book/

Oldest online log sequence 787

Next log sequence to archive 789

Current log sequence 789

SYS@book> @ check

檢查點佇列

當前時間髒塊數量

low_rba on_disk_rba on_disk_rba_scn( on_disk_rba_time(CP full checkpoint_rba full_checkpoint( full_checkpoint_tim diff_scn(on_disk_rdb-ch_scn) current_group SYSDATE CPDRT

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

789.5775.0 789.5955.0 13278979623 2019-03-12 11:20:53 789.1890.16 13278977341 2019-03-12 10:52:50 2282 2 2019-03-12 11:21:42 12

--//看看日誌應用的起點是否從low_rba開始.

SYS@book> alter database open ;

Database altered.

--//檢視alert.log日誌:

Beginning crash recovery of 1 threads

parallel recovery started with 23 processes

Started redo scan

Completed redo scan

read 90 KB redo, 12 data blocks need recovery

Started redo application at

Thread 1: logseq 789, block 5775

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~=>起點對應low_rba=789.5775.0

Recovery of Online Redo Log: Thread 1 Group 2 Seq 789 Reading mem 0

Mem# 0: /mnt/ramdisk/book/redo02.log

Completed redo application of 0.00MB

Completed crash recovery at

Thread 1: logseq 789, block 5956, scn 13278999624

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~=>結束對應on_disk_rba=789.5955.0加1個塊(512位元組redo),scn號對應on_disk_rba_scn+1.

12 data blocks read, 12 data blocks written, 90 redo k-bytes read

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

--//5955-5775 = 180,應用日誌180塊,日誌檔案每塊512位元組.

--//180*512/1024 = 90k,這些正好對上.

Tue Mar 12 11:23:26 2019

LGWR: STARTING ARCH PROCESSES

Tue Mar 12 11:23:26 2019

ARC0 started with pid=45, OS id=56804

ARC0: Archival started

LGWR: STARTING ARCH PROCESSES COMPLETE

ARC0: STARTING ARCH PROCESSES

Thread 1 advanced to log sequence 790 (thread open)

Thread 1 opened at log sequence 790

--//日誌切換使用新日誌.

Current log# 3 seq# 790 mem# 0: /mnt/ramdisk/book/redo03.log

Successful open of redo thread 1

MTTR advisory is disabled because FAST_START_MTTR_TARGET is not set

Tue Mar 12 11:23:27 2019

SMON: enabling cache recovery

--//也就是異常關閉後,crash recovery的起點從low_rba到on_disk_rba,完成後scn號+1,日誌塊號加1.日誌切換使用新日誌.

3.如果low_rba16=0xffffffff.ffffffff.ffff呢?

SYS@book> alter system checkpoint ;

System altered.

SYS@book> @ check

檢查點佇列

當前時間髒塊數量

low_rba on_disk_rba on_disk_rba_scn( on_disk_rba_time(CP full checkpoint_rba full_checkpoint( full_checkpoint_tim diff_scn(on_disk_rdb-ch_scn) current_group SYSDATE CPDRT

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

4294967295.429496729 790.659.0 13279000486 2019-03-12 11:32:34 790.658.16 13279000485 2019-03-12 11:32:33 1 3 2019-03-12 11:32:35 0

5.65535

--//等一會執行:

SYS@book> @ check

檢查點佇列

當前時間髒塊數量

low_rba on_disk_rba on_disk_rba_scn( on_disk_rba_time(CP full checkpoint_rba full_checkpoint( full_checkpoint_tim diff_scn(on_disk_rdb-ch_scn) current_group SYSDATE CPDRT

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

4294967295.429496729 790.678.0 13279000505 2019-03-12 11:32:53 790.658.16 13279000485 2019-03-12 11:32:33 20 3 2019-03-12 11:32:54 0

5.65535

--//你可以發現alter system checkpoint 後,如果沒有事務low_rba16=0xffffffff.ffffffff.ffff,而on_disk_rba一直在增加.而CPDRT=0.

--//似乎11g不知道為什麼在"空轉"(沒有事務產生的情況下)的情況,日誌也在不斷增加,不知道為什麼?

SYS@book> shutdown abort ;

ORACLE instance shut down.

SYS@book> startup mount

ORACLE instance started.

Total System Global Area 643084288 bytes

Fixed Size 2255872 bytes

Variable Size 205521920 bytes

Database Buffers 427819008 bytes

Redo Buffers 7487488 bytes

Database mounted.

SYS@book> @ check

檢查點佇列

當前時間髒塊數量

low_rba on_disk_rba on_disk_rba_scn( on_disk_rba_time(CP full checkpoint_rba full_checkpoint( full_checkpoint_tim diff_scn(on_disk_rdb-ch_scn) current_group SYSDATE CPDRT

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

4294967295.429496729 790.705.0 13279000532 2019-03-12 11:33:20 790.658.16 13279000485 2019-03-12 11:32:33 47 3 2019-03-12 11:36:09 0

5.65535

--//可以發現這個時候low_rba16=0xffffffff.ffffffff.ffff,這個時候恢復的起點從那裡開始,實際上從on_disk_rba開始,或者講根本沒

--//有恢復,CPDRT=0也是佐證,雖然當時on_disk_rba還在不斷增加.

SYS@book> alter database open ;

Database altered.

--//檢視alert.log:

Beginning crash recovery of 1 threads

parallel recovery started with 23 processes

Started redo scan

Completed redo scan

read 0 KB redo, 0 data blocks need recovery

Started redo application at

Thread 1: logseq 790, block 705, scn 13279000532

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~=>起點對應on_disk_rba=790.705.0

Recovery of Online Redo Log: Thread 1 Group 3 Seq 790 Reading mem 0

Mem# 0: /mnt/ramdisk/book/redo03.log

Completed redo application of 0.00MB

Completed crash recovery at

Thread 1: logseq 790, block 706, scn 13279020533

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~=>結束對應on_disk_rba=790.705.0加1個塊(512位元組redo),scn號對應on_disk_rba_scn+1.

0 data blocks read, 0 data blocks written, 0 redo k-bytes read

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~=> 日誌應用0K.

Tue Mar 12 11:39:33 2019

LGWR: STARTING ARCH PROCESSES

Tue Mar 12 11:39:33 2019

ARC0 started with pid=45, OS id=56980

ARC0: Archival started

LGWR: STARTING ARCH PROCESSES COMPLETE

ARC0: STARTING ARCH PROCESSES

Thread 1 advanced to log sequence 791 (thread open)

Thread 1 opened at log sequence 791

--//日誌切換使用新日誌.

Current log# 1 seq# 791 mem# 0: /mnt/ramdisk/book/redo01.log

Successful open of redo thread 1

MTTR advisory is disabled because FAST_START_MTTR_TARGET is not set

Tue Mar 12 11:39:34 2019

SMON: enabling cache recovery

4.我在原連結寫一個指令碼:

SCOTT@book> create table t1 as select * from all_objects ;

Table created.

$ cat a.sql

alter system checkpoint;

@ check

update scott.t1 set object_name=object_name where rownum=1 ;

commit;

host sleep 3

@ check

SYS@book> @ a.sql

System altered.

檢查點佇列

當前時間髒塊數量

low_rba on_disk_rba on_disk_rba_scn( on_disk_rba_time(CP full checkpoint_rba full_checkpoint( full_checkpoint_tim diff_scn(on_disk_rdb-ch_scn) current_group SYSDATE CPDRT

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

4294967295.429496729 791.21362.0 13279021797 2019-03-12 11:52:59 791.21362.16 13279021800 2019-03-12 11:53:00 -3 1 2019-03-12 11:53:01 0

5.65535

1 row updated.

Commit complete.

檢查點佇列

當前時間髒塊數量

low_rba on_disk_rba on_disk_rba_scn( on_disk_rba_time(CP full checkpoint_rba full_checkpoint( full_checkpoint_tim diff_scn(on_disk_rdb-ch_scn) current_group SYSDATE CPDRT

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

791.21363.0 791.21366.0 13279021805 2019-03-12 11:53:02 791.21362.16 13279021800 2019-03-12 11:53:00 5 1 2019-03-12 11:53:04 3

--//注意看發生事務前後的low_rba,on_disk_rba.不好描述,自己看.^_^.

--//一旦有事務產生,你可以發現low_rba不再是4294967295.4294967295.65535.

--//很奇怪不知道為什麼11g下在沒有事務的情況下會"空轉",這樣11g的日誌即使是很空閒的資料庫日誌增加也會比10g大.

5.看看10g的情況:

SYS@192.168.100.33:1521/test> @ ver1

PORT_STRING VERSION BANNER

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

x86_64/Linux 2.4.xx 10.2.0.4.0 Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi

SYS@192.168.100.33:1521/test> alter system checkpoint ;

System altered.

SYS@192.168.100.33:1521/test> @ check

檢查點佇列

當前時間髒塊數量

low_rba on_disk_rba on_disk_rba_scn( on_disk_rba_time(CP full checkpoint_rba full_checkpoint( full_checkpoint_tim diff_scn(on_disk_rdb-ch_scn) current_group SYSDATE CPDRT

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

4294967295.429496729 1497.42866.0 14987614992 2019-03-12 11:55:37 1497.42866.16 14987615031 2019-03-12 11:57:34 -39 3 2019-03-12 11:57:35 0

5.65535

SYS@192.168.100.33:1521/test> @ check

檢查點佇列

當前時間髒塊數量

low_rba on_disk_rba on_disk_rba_scn( on_disk_rba_time(CP full checkpoint_rba full_checkpoint( full_checkpoint_tim diff_scn(on_disk_rdb-ch_scn) current_group SYSDATE CPDRT

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

4294967295.429496729 1497.42866.0 14987614992 2019-03-12 11:55:37 1497.42866.16 14987615031 2019-03-12 11:57:34 -39 3 2019-03-12 11:58:29 0

5.65535

--//注意看執行時間2019-03-12 11:57:35 -2019-03-12 11:58:29 之間,沒有任何事務產生,on_disk_rba根本不變化.這樣10g日誌產生量

--//明顯比11g小.

6.我改上面的指令碼check.sql:

--//最後加入host sleep 1.執行如下:

$ rlsql -s -l sys/oracle as sysdba <<EOF

> $(seq 100| xargs -I{} cat /home/oracle/sqllaji/check.sql)

> EOF

檢查點佇列

當前時間髒塊數量

low_rba on_disk_rba on_disk_rba_scn( on_disk_rba_time(CP full checkpoint_rba full_checkpoint( full_checkpoint_tim diff_scn(on_disk_rdb-ch_scn) current_group SYSDATE CPDRT

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

791.24582.0 791.24711.0 13279023352 2019-03-12 12:11:39 791.21362.16 13279021800 2019-03-12 11:53:00 1552 1 2019-03-12 12:11:41 8

檢查點佇列

當前時間髒塊數量

low_rba on_disk_rba on_disk_rba_scn( on_disk_rba_time(CP full checkpoint_rba full_checkpoint( full_checkpoint_tim diff_scn(on_disk_rdb-ch_scn) current_group SYSDATE CPDRT

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

791.24582.0 791.24712.0 13279023353 2019-03-12 12:11:40 791.21362.16 13279021800 2019-03-12 11:53:00 1553 1 2019-03-12 12:11:42 8

檢查點佇列

當前時間髒塊數量

low_rba on_disk_rba on_disk_rba_scn( on_disk_rba_time(CP full checkpoint_rba full_checkpoint( full_checkpoint_tim diff_scn(on_disk_rdb-ch_scn) current_group SYSDATE CPDRT

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

791.24582.0 791.24713.0 13279023354 2019-03-12 12:11:41 791.21362.16 13279021800 2019-03-12 11:53:00 1554 1 2019-03-12 12:11:43 8

--//在沒有事務的情況下.每秒scn增加1,日誌塊增加1,是否更我訪問這些記憶體"表"有關,換1個方式測試,取消check.sql後面的host sleep 1,建立指令碼b.sql:

$ cat b.sql

@ check.sql

host sleep 30

@ check.sql

SYS@book> @ b.sql

檢查點佇列

當前時間髒塊數量

low_rba on_disk_rba on_disk_rba_scn( on_disk_rba_time(CP full checkpoint_rba full_checkpoint( full_checkpoint_tim diff_scn(on_disk_rdb-ch_scn) current_group SYSDATE CPDRT

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

791.24582.0 791.24852.0 13279023481 2019-03-12 12:13:41 791.21362.16 13279021800 2019-03-12 11:53:00 1681 1 2019-03-12 12:13:43 19

檢查點佇列

當前時間髒塊數量

low_rba on_disk_rba on_disk_rba_scn( on_disk_rba_time(CP full checkpoint_rba full_checkpoint( full_checkpoint_tim diff_scn(on_disk_rdb-ch_scn) current_group SYSDATE CPDRT

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

791.24582.0 791.24882.0 13279023511 2019-03-12 12:14:11 791.21362.16 13279021800 2019-03-12 11:53:00 1711 1 2019-03-12 12:14:13 19

--//確實每秒scn增加1,on_disk_rba也是增加每秒1塊.

[20190312]關於增量檢查點的疑問(補充).txt

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