[20190120]行連結遷移與dml.txt

--//昨天看的連結,裡面提到DML Tablescans 問題,

--//文章很難讀懂,不過有一個問題至少我以前沒注意,我一直以為如果修改出現行連結遷移的記錄,一定會在對應塊中使用

--//一個ITL槽.而且出現行遷移的記錄一般會在對應塊先建立dITL槽,我一直認為這個是事先預留,避免以後出現ITL槽不足的情況.

--//連結:http://blog.itpub.net/267265/viewspace-2152498/=>[20180402]行連結行遷移與ITL槽6.txt

--//另外作者在連結提到另外一種情況parallel DML.

--//連結http://blog.itpub.net/267265/viewspace-2152498/的一個例子測試.

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

2.建立測試例子:

create table t1 (

n1 number,

l1 varchar2(4000),

s1 varchar2(200),

l2 varchar2(4000),

s2 varchar2(200),

l3 varchar2(4000),

s3 varchar2(200)

);

--//L 表示 long長欄位, S表示 short短欄位.

insert into t1 (n1,l1,s1) values(0,rpad('X',4000,'X'),rpad('X',200,'X'));

commit;

insert into t1 (n1,l1) values(1,null);

commit;

update t1 set

l1 = rpad('A',4000),

s1 = rpad('A',200),

l2 = rpad('B',4000),

s2 = rpad('B',200),

l3 = rpad('C',4000),

s3 = rpad('C',200)

where

n1 = 1

;

commit;

execute dbms_stats.gather_table_stats(user,'t1');

update t1 set

s1 = lower(s1),

s2 = lower(s2),

s3 = lower(s3)

where

n1 = 1

;

--//注:沒提交.

SCOTT@book> @ xid

XIDUSN_XIDSLOT_XIDSQN

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

8.26.1883

alter system flush buffer_cache;

3.分析對應塊,透過bbed觀察::

SCOTT@book> select rowid,n1 from t1 ;

ROWID N1

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

AAAWKiAAEAAABMkAAA 0

AAAWKiAAEAAABMkAAB 1

SCOTT@book> @ rowid AAAWKiAAEAAABMkAAB

OBJECT FILE BLOCK ROW ROWID_DBA DBA TEXT

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

90786 4 4900 1 0x1001324 4,4900 alter system dump datafile 4 block 4900

--//首先透過bbed觀察:

BBED> set dba 4,4900

DBA 0x01001324 (16782116 4,4900)

BBED> x /rncccccc dba 4,4900 *kdbr[1]

rowdata[0] @3964

----------

flag@3964: 0x20 (KDRHFH)

lock@3965: 0x02

cols@3966: 0

nrid@3967:0x01001327.0

--//dba= 4,4900 ,僅僅包含nrid,指向下一個塊nrid=0x01001327.0(dba=4,4903),flag=0x20.僅僅包含head標識.繼續往下看:

BBED> set dba 0x01001327

DBA 0x01001327 (16782119 4,4903)

BBED> x /rncccccc dba 0x01001327 *kdbr[0]

rowdata[0] @4167

----------

flag@4167: 0x08 (KDRHFF)

lock@4168: 0x01

cols@4169: 2

hrid@4170:0x01001324.1

nrid@4176:0x01001326.0

col 0[2] @4182: 1

col 1[4000] @4185: A

--//dba = 4,4903. 包含2個欄位n1,l1. 指向下一個塊nrid=0x01001326.0(dba= 4,4902),前一個hrid=0x01001324.1(dba=4,4900).

--//flag=0x01,僅僅包含First標識.繼續往下看:

BBED> set dba 0x01001326

DBA 0x01001326 (16782118 4,4902)

BBED> x /rcccccc dba 0x01001326 *kdbr[0]

rowdata[0] @3975

----------

flag@3975: 0x00 (NONE)

lock@3976: 0x02

cols@3977: 2

nrid@3978:0x01001325.0

col 0[200] @3984: a

col 1[4000] @4185: B

--//dba=4,4902. 包含2個欄位s1,L2. 指向下一個塊nrid=0x01001325.0(dba= 4,4901),奇怪沒有hrid欄位.

--//flag=0x00. 沒有任何資訊.繼續:

BBED> set dba 0x01001325

DBA 0x01001325 (16782117 4,4901)

BBED> x /rcccccc dba 0x01001325 *kdbr[0]

rowdata[0] @3780

----------

flag@3780: 0x04 (KDRHFL)

lock@3781: 0x02

cols@3782: 3

col 0[200] @3783: b

col 1[4000] @3984: C

col 2[200] @7987: c

--//dba=4,4901. 包含3個欄位S2,L3,S3. 最後3個欄位.flag=0x02,包含LAST標識.

--//實際上還可以看出oracle是從最後欄位向前組織資料的.

4.轉儲看看:

SCOTT@book> @ xid

XIDUSN_XIDSLOT_XIDSQN

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

8.26.1883

alter system dump datafile 4 block 4900;

alter system dump datafile 4 block 4903;

alter system dump datafile 4 block 4902;

alter system dump datafile 4 block 4901;

--//dba = 4,4900

Block header dump: 0x01001324

Object id on Block? Y

seg/obj: 0x162a2 csc: 0x03.177320e3 itc: 2 flg: E typ: 1 - DATA

brn: 0 bdba: 0x1001320 ver: 0x01 opc: 0

inc: 0 exflg: 0

Itl Xid Uba Flag Lck Scn/Fsc

0x01 0x0008.014.0000075c 0x00c00123.03fa.07 C--- 0 scn 0x0003.17731d8b

0x02 0x0008.01a.0000075b 0x00c00123.03fa.2b ---- 1 fsc 0x0000.00000000

tab 0, row 1, @0xf18

tl: 9 fb: --H----- lb: 0x2 cc: 0

nrid: 0x01001327.0

--//0x1a=26,0x75b=1883

--//flag=--H-----. 使用ITL=0x2. xid=8.26.1883.

--//dba = 4,4903

Block header dump: 0x01001327

Object id on Block? Y

seg/obj: 0x162a2 csc: 0x03.17731d87 itc: 3 flg: E typ: 1 - DATA

brn: 0 bdba: 0x1001320 ver: 0x01 opc: 0

inc: 0 exflg: 0

Itl Xid Uba Flag Lck Scn/Fsc

0x01 0x0008.014.0000075c 0x00c00123.03fa.06 --U- 1 fsc 0x0000.17731d8b

0x02 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000

0x03 0x0000.000.00000000 0x00000000.0000.00 C--- 0 scn 0x0000.00000000

...

tab 0, row 0, @0xfcb

tl: 4021 fb: ----F--- lb: 0x1 cc: 2

hrid: 0x01001324.1

nrid: 0x01001326.0

col 0: [ 2] c1 02

col 1: [4000]

41 20 20

--//flag=----F---,使用ITL=0x1.注意看這個ITL槽指向的xid並不是0x0008.01a.0000075b(而是0x0008.014.0000075c).

--//這個塊僅僅包含N1,L1欄位,並沒有包含要修改S1,S2,S3欄位.

--//也就是dml並沒有在該塊修改ITL槽.

--//dba = 4,4902

Block header dump: 0x01001326

Object id on Block? Y

seg/obj: 0x162a2 csc: 0x03.177320e4 itc: 3 flg: E typ: 1 - DATA

brn: 0 bdba: 0x1001320 ver: 0x01 opc: 0

inc: 0 exflg: 0

Itl Xid Uba Flag Lck Scn/Fsc

0x01 0x0008.014.0000075c 0x00c00123.03fa.05 C--- 0 scn 0x0003.17731d8b

0x02 0x0008.01a.0000075b 0x00c00123.03fa.2c ---- 1 fsc 0x0000.00000000

0x03 0x0000.000.00000000 0x00000000.0000.00 C--- 0 scn 0x0000.00000000

...

block_row_dump:

tab 0, row 0, @0xf0b

tl: 4213 fb: -------- lb: 0x2 cc: 2

nrid: 0x01001325.0

col 0: [200]

61 20

--//flag=NONE.使用ITL=0x2,xid=0x0008.01a.0000075b

--//dba = 4,4901

Block header dump: 0x01001325

Object id on Block? Y

seg/obj: 0x162a2 csc: 0x03.177320e4 itc: 3 flg: E typ: 1 - DATA

brn: 0 bdba: 0x1001320 ver: 0x01 opc: 0

inc: 0 exflg: 0

Itl Xid Uba Flag Lck Scn/Fsc

0x01 0x0008.014.0000075c 0x00c00123.03fa.04 C--- 0 scn 0x0003.17731d8b

0x02 0x0008.01a.0000075b 0x00c00123.03fa.2d ---- 1 fsc 0x0000.00000000

0x03 0x0000.000.00000000 0x00000000.0000.00 C--- 0 scn 0x0000.00000000

tab 0, row 0, @0xe48

tl: 4408 fb: -----L-- lb: 0x2 cc: 3

col 0: [200]

62 20 20 20 20

--//flag=-----L--.使用ITL=0x2,xid=0x0008.01a.0000075b

--//從以上分析可以看出如果dml修改在該塊中沒有對應記錄,並不會使用ITL槽,這個是我以前沒有注意的細節問題.

[20190120]行連結遷移與dml.txt

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