[ODI] chapter2 what is "undo record chaining"?
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- Undo record chaining allows Oracle to rollback multiple transactions by linking undo records together in a chain. - When an update is made, an undo record is generated and added to the undo block. A new record contains the before image of the update. - Undo records for a transaction are chained together by transaction ID and sequence number. This allows Oracle to efficiently rollback a whole transaction by traversing the undo record chain.
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[ODI] chapter2 what is "undo record chaining"?
- 1. Oracle Deep Internal report no. 002 What is “Undo record chaining”? Research & Contents Team
- 2. Undo record chaining은 실제로 어떻게 움직이나? 02 Lee Kun Oh (李根五) Kwon Kon Woo (權建佑)
- 3. Cited from http://wiki.gurubee.net/display/STUDY/1st_Undo "Undo record chain" mechanism as explained in Gurubee site It's so difficult to understand only through the book. I'd like to check internal actual situation of oracle with my own eyes
- 4. SGA Undo Segment Shared Pool Buffer Cache Undo Header index state cflags wrap# uel scn dba -------------------------------------------------------------------------------- 0x00 9 0x00 0x04ec 0x0001 0x0000.003d6d72 0x00000000 0x01 9 0x00 0x04ec 0x0002 0x0000.003d6d72 0x00000000 0x02 9 0x00 0x04ec 0x0003 0x0000.003d6d72 0x00000000 Undo Block * Rec #0x1 BH Data Block ITL Itl Xid Uba Flag Lck Scn/Fsc Rows block_row_dump: tab 0, row 0, @0x1f88 tl: 16 fb: --H-FL-- lb: 0x1 cc: 2 col 0: [10] 31 20 20 20 20 20 20 20 20 20 col 1: [ 1] 41 ASCII HEXA code 41 => Value ‘A’ V$transaction XID_INFO UBA_INFO TXN_INFO -------------------------- --------------- -------------------- addr : status : IDLE xidusn : ubafil : start_date : 2015-12-10 10:52:46 xidslot : ubablk : ses_addr : 000000006B21CC20 xidsqn : ubasqn : 0. Initial state when a value of "A" is entered (The first stage before update)
- 5. SGA Undo Segment Shared Pool Buffer Cache 1. UPDATE T1 SET C2='B' v$transaction XID_INFO UBA_INFO TXN_INFO -------------------------- --------------- -------------------------------- addr : 0000000069B24E78 ubafil : 6 status : ACTIVE xidusn : 10 ubablk : 210 start_date : 2016-01-13 18:57:04 xidslot : 0 ubasqn : 532 ses_addr : 000000006B21CC20 xidsqn : 1424 ubarec : 1 Undo Header index state cflags wrap# uel scn dba ---------------------------------------------------------------- 0x00 10 0x80 0x0590 0x0000 0x0000.004c2039 0x018000d2 0x01 9 0x00 0x058f 0x0002 0x0000.004bca7f 0x00000000 Undo Block BH (0x643fb068) file#: 6 rdba: 0x018000d2 (6/210) class: 36 ba: 0x643ce000 xid: 0x000a.000.00000590 seq: 0x214 cnt: 0x1 irb: 0x1 icl: 0x0 flg: 0x0000 Rec Offset Rec Offset Rec Offset Rec Offset Rec Offset --------------------------------------------------------------------------- 0x01 0x1f44 *----------------------------- * Rec #0x1 slt: 0x00 objn: 70870(0x000114d6) objd: 70870 tblspc: 5(0x00000005) * Layer: 11 (Row) opc: 1 rci 0x00 op: Z itli: 2 ispac: 0 maxfr: 4858 vect = 11 col 1: [ 1] 41 BH (0x643fb1a0) file#: 5 rdba: 0x0140dcab (5/56491) class: 1 ba: 0x643d0000 st: XCURRENT md: NULL fpin: 'kdswh11: kdst_fetch' tch: 1 Itl Xid Uba Flag Lck Scn/Fsc 0x01 0x0006.000.0000056a 0x00000000.0000.00 C--- 0 scn 0x0000.004c2027 0x02 0x000a.000.00000590 0x018000d2.0214.01 ---- 1 fsc 0x0000.00000000 0x03 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000 tl: 16 fb: --H-FL-- lb: 0x2 cc: 2 col 0: [10] 31 20 20 20 20 20 20 20 20 20 col 1: [ 1] 42 BH (0x643fb2d8) file#: 5 rdba: 0x0140dcab (5/56491) class: 1 ba: 0x643d2000 st: CR md: NULL fpin: 'kdswh11: kdst_fetch' tch: 1 Itl Xid Uba Flag Lck Scn/Fsc 0x01 0x0006.000.0000056a 0x00000000.0000.00 C--- 0 scn 0x0000.004c2027 0x02 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000 0x03 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000 tl: 16 fb: --H-FL-- lb: 0x0 cc: 2 col 0: [10] 31 20 20 20 20 20 20 20 20 20 col 1: [ 1] 41 Before Image ASCII HEXA code 41 => Value ‘A’ Before Image ASCII HEXA code 41 => Value ‘A’ After Image ASCII HEXA code 43 => Value ‘C’ Uba+seq+record#UPDATE T1 SET c2 = ‘B’
- 6. SGA Undo Segment Shared Pool Buffer Cache 2. UPDATE T1 SET C2=‘C' v$transaction XID_INFO UBA_INFO TXN_INFO -------------------------- --------------- -------------------------------- addr : 0000000069B24E78 ubafil : 6 status : ACTIVE xidusn : 10 ubablk : 210 start_date : 2016-01-13 18:57:04 xidslot : 0 ubasqn : 532 ses_addr : 000000006B21CC20 xidsqn : 1424 ubarec : 2 Undo Header index state cflags wrap# uel scn dba ---------------------------------------------------------------- 0x00 10 0x80 0x0590 0x0000 0x0000.004c2039 0x018000d2 0x01 9 0x00 0x058f 0x0002 0x0000.004bca7f 0x00000000 Undo Block BH (0x643fb068) file#: 6 rdba: 0x018000d2 (6/210) class: 36 ba: 0x643ce000 xid: 0x000a.000.00000590 seq: 0x214 cnt: 0x2 irb: 0x2 icl: 0x0 flg: 0x0000 Rec Offset Rec Offset Rec Offset Rec Offset Rec Offset --------------------------------------------------------------------------- 0x01 0x1f44 0x02 0x1ecc *----------------------------- * Rec #0x1 slt: 0x00 objn: 70870(0x000114d6) objd: 70870 tblspc: 5(0x00000005) * Layer: 11 (Row) opc: 1 rci 0x00 op: Z itli: 2 ispac: 0 maxfr: 4858 vect = 11 col 1: [ 1] 41 *----------------------------- * Rec #0x2 slt: 0x00 objn: 70870(0x000114d6) objd: 70870 tblspc: 5(0x00000005) * Layer: 11 (Row) opc: 1 rci 0x01 op: C uba: 0x018000d2.0214.01 itli: 2 ispac: 0 maxfr: 4858 vect = 11 col 1: [ 1] 42 BH (0x643f8e48) file#: 5 rdba: 0x0140dcab (5/56491) class: 1 ba: 0x64396000 st: XCURRENT md: NULL fpin: 'kdswh11: kdst_fetch' tch: 1 Itl Xid Uba Flag Lck Scn/Fsc 0x01 0x0006.000.0000056a 0x00000000.0000.00 C--- 0 scn 0x0000.004c2027 0x02 0x000a.000.00000590 0x018000d2.0214.02 ---- 1 fsc 0x0000.00000000 0x03 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000 tl: 16 fb: --H-FL-- lb: 0x2 cc: 2 col 0: [10] 31 20 20 20 20 20 20 20 20 20 col 1: [ 1] 43 BH (0x643fb2d8) file#: 5 rdba: 0x0140dcab (5/56491) class: 1 ba: 0x643d2000 st: CR md: NULL fpin: 'kdswh11: kdst_fetch' tch: 1 Itl Xid Uba Flag Lck Scn/Fsc 0x01 0x0006.000.0000056a 0x00000000.0000.00 C--- 0 scn 0x0000.004c2027 0x02 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000 0x03 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000 tl: 16 fb: --H-FL-- lb: 0x0 cc: 2 col 0: [10] 31 20 20 20 20 20 20 20 20 20 col 1: [ 1] 41 BH (0x643fb1a0) file#: 5 rdba: 0x0140dcab (5/56491) class: 1 ba: 0x643d0000 st: CR md: NULL fpin: 'kdswh11: kdst_fetch' tch: 1 Itl Xid Uba Flag Lck Scn/Fsc 0x01 0x0006.000.0000056a 0x00000000.0000.00 C--- 0 scn 0x0000.004c2027 0x02 0x000a.000.00000590 0x018000d2.0214.01 ---- 1 fsc 0x0000.00000000 0x03 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000 tl: 16 fb: --H-FL-- lb: 0x2 cc: 2 col 0: [10] 31 20 20 20 20 20 20 20 20 20 col 1: [ 1] 42 After Image ASCII HEXA code 43 => Value ‘C’ Before Image ASCII HEXA code 42 => Value ‘B’ Before Image ASCII HEXA code 42 => Value ‘B’ Before Image ASCII HEXA code 41 => Value ‘A’ UPDATE T1 SET c2 = ‘C’
- 7. SGA Undo Segment Shared Pool Buffer Cache 3. UPDATE T1 SET C2=‘D' v$transaction XID_INFO UBA_INFO TXN_INFO -------------------------- --------------- -------------------------------- addr : 0000000069B24E78 ubafil : 6 status : ACTIVE xidusn : 10 ubablk : 210 start_date : 2016-01-13 18:57:04 xidslot : 0 ubasqn : 532 ses_addr : 000000006B21CC20 xidsqn : 1424 ubarec : 3 Undo Header index state cflags wrap# uel scn dba ---------------------------------------------------------------- 0x00 10 0x80 0x0590 0x0000 0x0000.004c2039 0x018000d2 0x01 9 0x00 0x058f 0x0002 0x0000.004bca7f 0x00000000 Undo Block BH (0x643fb068) file#: 6 rdba: 0x018000d2 (6/210) class: 36 ba: 0x643ce000 xid: 0x000a.000.00000590 seq: 0x214 cnt: 0x3 irb: 0x3 icl: 0x0 flg: 0x0000 Rec Offset Rec Offset Rec Offset Rec Offset Rec Offset --------------------------------------------------------------------------- 0x01 0x1f44 0x02 0x1ecc 0x03 0x1e54 *----------------------------- * Rec #0x1 slt: 0x00 objn: 70870(0x000114d6) objd: 70870 tblspc: 5(0x00000005) * Layer: 11 (Row) opc: 1 rci 0x00 op: Z itli: 2 ispac: 0 maxfr: 4858 vect = 11 col 1: [ 1] 41 *----------------------------- * Rec #0x2 slt: 0x00 objn: 70870(0x000114d6) objd: 70870 tblspc: 5(0x00000005) * Layer: 11 (Row) opc: 1 rci 0x01 op: C uba: 0x018000d2.0214.01 itli: 2 ispac: 0 maxfr: 4858 vect = 11 col 1: [ 1] 42 *----------------------------- * Rec #0x3 slt: 0x00 objn: 70870(0x000114d6) objd: 70870 tblspc: 5(0x00000005) * Layer: 11 (Row) opc: 1 rci 0x02 op: C uba: 0x018000d2.0214.02 itli: 2 ispac: 0 maxfr: 4858 vect = 11 col 1: [ 1] 43 BH (0x643f8968) file#: 5 rdba: 0x0140dcab (5/56491) class: 1 ba: 0x6438e000 st: XCURRENT md: NULL fpin: 'kdswh11: kdst_fetch' tch: 1 Itl Xid Uba Flag Lck Scn/Fsc 0x01 0x0006.000.0000056a 0x00000000.0000.00 C--- 0 scn 0x0000.004c2027 0x02 0x000a.000.00000590 0x018000d2.0214.03 ---- 1 fsc 0x0000.00000000 0x03 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000 tl: 16 fb: --H-FL-- lb: 0x2 cc: 2 col 0: [10] 31 20 20 20 20 20 20 20 20 20 col 1: [ 1] 44 BH (0x643fb2d8) file#: 5 rdba: 0x0140dcab (5/56491) class: 1 ba: 0x643d2000 st: CR md: NULL fpin: 'kdswh11: kdst_fetch' tch: 1 Itl Xid Uba Flag Lck Scn/Fsc 0x01 0x0006.000.0000056a 0x00000000.0000.00 C--- 0 scn 0x0000.004c2027 0x02 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000 0x03 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000 tl: 16 fb: --H-FL-- lb: 0x0 cc: 2 col 0: [10] 31 20 20 20 20 20 20 20 20 20 col 1: [ 1] 41 BH (0x643fb1a0) file#: 5 rdba: 0x0140dcab (5/56491) class: 1 ba: 0x643d0000 st: CR md: NULL fpin: 'kdswh11: kdst_fetch' tch: 1 Itl Xid Uba Flag Lck Scn/Fsc 0x01 0x0006.000.0000056a 0x00000000.0000.00 C--- 0 scn 0x0000.004c2027 0x02 0x000a.000.00000590 0x018000d2.0214.01 ---- 1 fsc 0x0000.00000000 0x03 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000 tl: 16 fb: --H-FL-- lb: 0x2 cc: 2 col 0: [10] 31 20 20 20 20 20 20 20 20 20 col 1: [ 1] 42 BH (0x643f8e48) file#: 5 rdba: 0x0140dcab (5/56491) class: 1 ba: 0x64396000 st: CR md: NULL fpin: 'kdswh11: kdst_fetch' tch: 1 Itl Xid Uba Flag Lck Scn/Fsc 0x01 0x0006.000.0000056a 0x00000000.0000.00 C--- 0 scn 0x0000.004c2027 0x02 0x000a.000.00000590 0x018000d2.0214.02 ---- 1 fsc 0x0000.00000000 0x03 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000 tl: 16 fb: --H-FL-- lb: 0x2 cc: 2 col 0: [10] 31 20 20 20 20 20 20 20 20 20 col 1: [ 1] 43 Before Image ASCII HEXA code 43 => Value ‘C’ After Image ASCII HEXA code 44 => Value ‘D’ Before Image ASCII HEXA code 43 => Value ‘C’ Before Image ASCII HEXA code 42 => Value ‘B’ Before Image ASCII HEXA code 41 => Value ‘A’ UPDATE T1 SET c2 = ‘D’
- 8. SGA Undo Segment Shared Pool Buffer Cache 4. Summary v$transaction XID_INFO UBA_INFO TXN_INFO -------------------------- --------------- -------------------------------- addr : 0000000069B24E78 ubafil : 6 status : ACTIVE xidusn : 10 ubablk : 210 start_date : 2016-01-13 18:57:04 xidslot : 0 ubasqn : 532 ses_addr : 000000006B21CC20 xidsqn : 1424 ubarec : 3 Undo Header index state cflags wrap# uel scn dba ---------------------------------------------------------------- 0x00 10 0x80 0x0590 0x0000 0x0000.004c2039 0x018000d2 0x01 9 0x00 0x058f 0x0002 0x0000.004bca7f 0x00000000 Undo Block BH (0x643fb068) file#: 6 rdba: 0x018000d2 (6/210) class: 36 ba: 0x643ce000 xid: 0x000a.000.00000590 seq: 0x214 cnt: 0x3 irb: 0x3 icl: 0x0 flg: 0x0000 Rec Offset Rec Offset Rec Offset Rec Offset Rec Offset --------------------------------------------------------------------------- 0x01 0x1f44 0x02 0x1ecc 0x03 0x1e54 *----------------------------- * Rec #0x1 slt: 0x00 objn: 70870(0x000114d6) objd: 70870 tblspc: 5(0x00000005) * Layer: 11 (Row) opc: 1 rci 0x00 op: Z itli: 2 ispac: 0 maxfr: 4858 vect = 11 col 1: [ 1] 41 *----------------------------- * Rec #0x2 slt: 0x00 objn: 70870(0x000114d6) objd: 70870 tblspc: 5(0x00000005) * Layer: 11 (Row) opc: 1 rci 0x01 op: C uba: 0x018000d2.0214.01 itli: 2 ispac: 0 maxfr: 4858 vect = 11 col 1: [ 1] 42 *----------------------------- * Rec #0x3 slt: 0x00 objn: 70870(0x000114d6) objd: 70870 tblspc: 5(0x00000005) * Layer: 11 (Row) opc: 1 rci 0x02 op: C uba: 0x018000d2.0214.02 itli: 2 ispac: 0 maxfr: 4858 vect = 11 col 1: [ 1] 43 BH (0x643f8968) file#: 5 rdba: 0x0140dcab (5/56491) class: 1 ba: 0x6438e000 st: XCURRENT md: NULL fpin: 'kdswh11: kdst_fetch' tch: 1 Itl Xid Uba Flag Lck Scn/Fsc 0x01 0x0006.000.0000056a 0x00000000.0000.00 C--- 0 scn 0x0000.004c2027 0x02 0x000a.000.00000590 0x018000d2.0214.03 ---- 1 fsc 0x0000.00000000 0x03 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000 tl: 16 fb: --H-FL-- lb: 0x2 cc: 2 col 0: [10] 31 20 20 20 20 20 20 20 20 20 col 1: [ 1] 44 BH (0x643fb2d8) file#: 5 rdba: 0x0140dcab (5/56491) class: 1 ba: 0x643d2000 st: CR md: NULL fpin: 'kdswh11: kdst_fetch' tch: 1 Itl Xid Uba Flag Lck Scn/Fsc 0x01 0x0006.000.0000056a 0x00000000.0000.00 C--- 0 scn 0x0000.004c2027 0x02 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000 0x03 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000 tl: 16 fb: --H-FL-- lb: 0x0 cc: 2 col 0: [10] 31 20 20 20 20 20 20 20 20 20 col 1: [ 1] 41 BH (0x643fb1a0) file#: 5 rdba: 0x0140dcab (5/56491) class: 1 ba: 0x643d0000 st: CR md: NULL fpin: 'kdswh11: kdst_fetch' tch: 1 Itl Xid Uba Flag Lck Scn/Fsc 0x01 0x0006.000.0000056a 0x00000000.0000.00 C--- 0 scn 0x0000.004c2027 0x02 0x000a.000.00000590 0x018000d2.0214.01 ---- 1 fsc 0x0000.00000000 0x03 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000 tl: 16 fb: --H-FL-- lb: 0x2 cc: 2 col 0: [10] 31 20 20 20 20 20 20 20 20 20 col 1: [ 1] 42 BH (0x643f8e48) file#: 5 rdba: 0x0140dcab (5/56491) class: 1 ba: 0x64396000 st: CR md: NULL fpin: 'kdswh11: kdst_fetch' tch: 1 Itl Xid Uba Flag Lck Scn/Fsc 0x01 0x0006.000.0000056a 0x00000000.0000.00 C--- 0 scn 0x0000.004c2027 0x02 0x000a.000.00000590 0x018000d2.0214.02 ---- 1 fsc 0x0000.00000000 0x03 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000 tl: 16 fb: --H-FL-- lb: 0x2 cc: 2 col 0: [10] 31 20 20 20 20 20 20 20 20 20 col 1: [ 1] 43 Before Image ASCII HEXA code 43 => Value ‘C’ After Image ASCII HEXA code 44 => Value ‘D’ Before Image ASCII HEXA code 43 => Value ‘C’ Before Image ASCII HEXA code 42 => Value ‘B’ Before Image ASCII HEXA code 41 => Value ‘A’ op: C uba: 0x018000d2.0214.02 op: C uba: 0x018000d2.0214.01 op: Z Rec #0x1 Rec #0x2 Rec #0x3
- 9. Oracle Deep Internal More information https://youtu.be/c7EmzCd7buk Blog Video E-mail NAVER http://cafe.naver.com/playexem ITPUB http://blog.itpub.net/31135309/ Wordpress https://playexem.wordpress.com/ Youtube https://www.youtube.com/channel/ UC5wKR_-A0eL_Pn_EMzoauJg playexem@ex-em.com playexem@naver.com For more information, or to schedule an on-site education, contact via blog or e-mail Kon Woo, Kwon Kun Oh, Lee Sook jin, Kim Dae Deok, Lee