CSE 444: Database Internals - courses.cs.washington.edu · 2019-05-19 · Tk, or transactions that...

CSE444:DatabaseInternals

Section6:Transactions- Recovery

Reviewinthissection

1. UNDOlogging

2. REDOlogging

3. UpdatingARIESDataStructures

UndoLogging

• TwoRules:– 1.IfatransactionwriteselementX,thenthelogrecordofthisupdate<T,X,v>mustbewrittentodiskbeforethenewvalueofX iswrittentodisk.

– 2.Ifatransactioncommits,thentheCOMMITmustbewrittentodiskonlyafterallelementschangedbythetransactionhavebeenwrittentodisk.

Action T Mem A Mem B Disk A Disk B Log

<START T>

INPUT(A) 8 8 8

READ(A,t) 8 8 8 8

t:=t*2 16 8 8 8

WRITE(A,t) 16 16 8 8 <T,A,8>

INPUT(B) 16 16 8 8 8

READ(B,t) 8 16 8 8 8

t:=t*2 16 16 8 8 8

WRITE(B,t) 16 16 16 8 8 <T,B,8>

OUTPUT(A) 16 16 16 16 8

OUTPUT(B) 16 16 16 16 16

COMMIT <COMMIT T>

4

UNDOLOGRULES

1. <T,X,v>beforeOUTPUT(X)2. OUTPUT(X)before<COMMIT>

Whenrecovering(withUNDOlogging)…

• Wecannotsimplyignorethelogbeforearecentcommito Manytransactionsinterleaveatonce.Ifwetruncate

beforeacommitforatransaction,anyinformationaboutthoseunfinishedtransactionswouldbelost.

• Instead,wecanusecheckpointthelogperiodically…

Review:Checkpointing

• Checkpointing (naïve)– Writea<STARTCKPT(T1,…,Tk)>.Flushlogtodisk– Stopacceptingnewtransactions– Waituntilallactivetransactionsabort/commit– Write<CKPT>.Flushlogtodisk.– Resume acceptingtransactions

• Nonquiescent Checkpointing– Writea<STARTCKPT(T1,…,Tk)>.Flushlogtodisk– Continuenormaloperation– WhenallofT1,…,Tk havecompleted,write<ENDCKPT>.Flushlogtodisk– Moreefficient,systemdoesnotseemtobestalled

Problem1.UNDOLogging

LSN1 <START T1>LSN2 <T1 X 5>LSN3 <START T2>LSN4 <T1 Y 7>LSN5 <T2 X 9>LSN6 <START T3>LSN7 <T3 Z 11>LSN8 <COMMIT T1>LSN9 <START CKPT(T2,T3)>LSN10 <T2 X 13>LSN11 <T3 Y 15>

*CRASH*

1.Showhowfarbackintherecoverymanagerneedstoreadthelog

(whichLSNdoweneedtoreadupto?)

UNDO:Howfartoscanlogfromtheend?

• Case1:See<ENDCKPT>first– Allincompletetransactions

beganafter<STARTCKPT…>

• Case2:See<STARTCKPT(T1..TK)>first– Incompletetransactions

beganafter<STARTCKPT…>orincompleteonesamongT1..TK

– Findtheearliest<STARTTi>amongthem

– Atmostwehavetogountiltheprevious<STARTCKPT>…<ENDCKPT>


*CRASH*



*CRASH*

1.Showhowfarbackintherecoverymanagerneedstoreadthelog

(writetheearliestLSN)

LSN3(startoftheearliesttransactionamongincompletetransactions)



*CRASH*

2.Showtheactionsoftherecoverymanagerduringrecovery.



*CRASH*

2.Showtheactionsoftherecoverymanagerduringrecovery.

Y=15X=13Z=11X=9

RedoLogging

• OneRule:– 1.BeforemodifyinganyelementXondisk,alllogrecordspertainingtothismodification(<T,X,v>andthe<COMMITT>),mustappearondisk.

Action T Mem A Mem B Disk A Disk B Log

<START T>

READ(A,t) 8 8 8 8

t:=t*2 16 8 8 8

WRITE(A,t) 16 16 8 8 <T,A,16>

READ(B,t) 8 16 8 8 8

t:=t*2 16 16 8 8 8

WRITE(B,t) 16 16 16 8 8 <T,B,16>

<COMMIT T>

OUTPUT(A) 16 16 16 16 8

OUTPUT(B) 16 16 16 16 16

13

REDOLOGRULE

Both<T,X,v>and<COMMIT>beforeOUTPUT(X)v=newvalue

Problem2:REDOLogging

1. <STARTT1>2. <T1,A,10>3. <STARTT2>4. <T2,B,5>5. <T1,C,7>6. <STARTT3>7. <T3,D,12>8. <COMMITT1>9. <STARTCKPT????>10.<STARTT4>

11.<T2,E,5>12.<COMMITT2>13.<T3,F,1>14.<T4,G,15>15.<ENDCKPT>16.<COMMITT3>17.<STARTT5>18.<T5,H,3>19.<STARTCKPT????>20.<COMMITT5>*CRASH*

1.Whatarethecorrectvaluesofthetwo<STARTCKPT????>records?


1. <STARTT1>2. <T1,A,10>3. <STARTT2>4. <T2,B,5>5. <T1,C,7>6. <STARTT3>7. <T3,D,12>8. <COMMITT1>9. <STARTCKPT????>10.<STARTT4>

11.<T2,E,5>12.<COMMITT2>13.<T3,F,1>14.<T4,G,15>15.<ENDCKPT>16.<COMMITT3>17.<STARTT5>18.<T5,H,3>19.<STARTCKPT????>20.<COMMITT5>

1.Whatarethecorrectvaluesofthetwo<STARTCKPT????>records?

FirstSTARTCKPT:<STARTCKPT(T2,T3)>

SecondSTARTCKPT:<STARTCKPT(T4,T5)>

Problem2:REDOLogging(Checkpoint)

1. <STARTT1>2. <T1,A,10>3. <STARTT2>4. <T2,B,5>5. <T1,C,7>6. <STARTT3>7. <T3,D,12>8. <COMMITT1>9. <STARTCKPTT2,T3>10.<STARTT4>

11.<T2,E,5>12.<COMMITT2>13.<T3,F,1>14.<T4,G,15>15.<ENDCKPT>16.<COMMITT3>17.<STARTT5>18.<T5,H,3>19.<STARTCKPTT4,T5>20.<COMMITT5>

NOTE:

<CommitT3>after<ENDCKPT>

WhatareweCKPTing?

Thetransactionsthatcommittedbefore<STARTCKPT>

REDO:Howfartoscanlogfromthestart?

• Identifycommittedtransactions

• Case1:See<ENDCKPT>first– Allcommittedtransactionsbefore<STARTCKPT(T1..TK)>arewritten– ConsiderT1..Tk,ortransactionsthatstartedafter<STARTCKPT…>,

tracebackuntilearliest<STARTTi>

• Case2:See<STARTCKPT(T1..TK)>first– CommittedtransactionsbeforeSTARTCKPTmightnothavebeen

written– Findprevious<ENDCKPT>,itsmatching<STARTCKPT(S1,…Sm)>– Redocommittedtransactionsthatstartedafter<STARTCKPTT1..Tk>

orS1..Sm



11.<T2,E,5>12.<COMMITT2>13.<T3,F,1>14.<T4,G,15>15.<ENDCKPT>16.<COMMITT3>17.<STARTT5>18.<T5,H,3>19.<STARTCKPTT4,T5 >20.<COMMITT5>

2.Whatfragmentofthelogdoestherecoverymanagerneedtoread?



11.<T2,E,5>12.<COMMITT2>13.<T3,F,1>14.<T4,G,15>15.<ENDCKPT>16.<COMMITT3>17.<STARTT5>18.<T5,H,3>19.<STARTCKPTT4,T5>20.<COMMITT5>

2.Whatfragmentofthelogdoestherecoverymanagerneedtoread?•WeknowtherewasacommitforT5.

•InthepreviousSTARTCKPT,T2andT3werethetwoactivetransactions.Bothtransactionscommittedandmustthusberedone.

•T2wastheearliestone




3.Whichelementsarerecoveredbytheredorecoverymanager?computetheirvaluesafterrecovery.




3.Whichelementsarerecoveredbytheredorecoverymanager?computetheirvaluesafterrecovery.

AllchangesbyT2,T3,T5(committed)B=5D=12E=5F=1H=3

Review:ARIESDataStructures(UNDO/REDOLogging)

Example.1. T1000 changesthevalueofAfrom“abc”to“def” onpageP5002. T2000 changesthevalueofBfrom“hij”to“klm” onpageP6003. T2000 changesthevalueofDfrom“mnp”to“qrs”onpageP5004. T1000 changesthevalueofCfrom“tuv”to“wxy”onpageP5055. T2000 commitsandtheendlogrecordiswritten6. T1000 changesthevalueofEfrom“pq”to“rs” onpageP7007. P600 isflushedtodisk8. Crash!!

SeeSection7

P500PageLSN= -

P600PageLSN= -

P505PageLSN= -

P700PageLSN= -

B=hij

ARIES Data StructurespageID recLSN LSN prevLSN tID pID Log entry Type undoNextLSN

101

Dirty page table Log

transID lastLSN statusTransaction table

Buffer Pool

24

A=abc D=mnp

C=tuv E=pq

P500PageLSN= -

P600PageLSN= -

P505PageLSN= -

P700PageLSN= -

B=hij

Disk

A=abc D=mnp

C=tuv E=pq

P500PageLSN= -

P600PageLSN= -

P505PageLSN= -

P700PageLSN= -

B=hij

pageID recLSN LSN prevLSN tID pID Log entry Type undoNextLSN

101


transID lastLSN statusTransaction table

Buffer Pool

25

A=abc D=mnp

C=tuv E=pq

P500PageLSN= -

P600PageLSN= -

P505PageLSN= -

P700PageLSN= -

B=hij

Disk

A=abc D=mnp

C=tuv E=pq

Firstoperation:1.T1000 changesthevalueofAfrom“abc”to“def” onpageP500?

P500PageLSN= 101

P600PageLSN= -

P505PageLSN= -

P700PageLSN= -

B=hij

pageID recLSNP500 101

LSN prevLSN tID pID Log entry Type undoNextLSN

101 - T1000 P500 Write A“abc” -> “def”

Update -


transID lastLSN status

T1000 101 Running

Transaction table

Buffer Pool

26

A=defD=mnp

C=tuv E=pq

P500PageLSN= -

P600PageLSN= -

P505PageLSN= -

P700PageLSN= -

B=hij

Disk

A=abc D=mnp

C=tuv E=pq

Changes1.T1000 changesthevalueofAfrom“abc”to“def” onpageP500

P500PageLSN= 101

P600PageLSN= -

P505PageLSN= -

P700PageLSN= -

B=hij



101 - T1000 P500 Write A“abc” -> “def”

Update -



T1000 101 Running

Transaction table

Buffer Pool

27

A=defD=mnp

C=tuv E=pq

P500PageLSN= -

P600PageLSN= -

P505PageLSN= -

P700PageLSN= -

B=hij

Disk

A=abc D=mnp

C=tuv E=pq

Next:2.T2000 changesthevalueofBfrom“hij”to“klm” onpageP600?

P500PageLSN= 101

P600PageLSN= 102

P505PageLSN= -

P700PageLSN= -

B=klm


P600 102


101 - T1000 P500 Write A“abc” -> “def”

Update -102 - T2000 P600 Write B

“hij” -> “klm”Update



T1000 101 Running

T2000 102 Running

Transaction table

Buffer Pool

28

A=def D=mnp

C=tuv E=pq

P500PageLSN= -

P600PageLSN= -

P505PageLSN= -

P700PageLSN= -

B=hij

Disk

A=abc D=mnp

C=tuv E=pq

Changes:2.T2000 changesthevalueofBfrom“hij”to“klm” onpageP600?

P500PageLSN= 101

P600PageLSN= 102

P505PageLSN= -

P700PageLSN= -

B=klm


P600 102


101 - T1000 P500 Write A“abc” -> “def”

Update -102 - T2000 P600 Write B

“hij” -> “klm”Update



T1000 101 Running

T2000 102 Running

Transaction table

Buffer Pool

29

A=def D=mnp

C=tuv E=pq

P500PageLSN= -

P600PageLSN= -

P505PageLSN= -

P700PageLSN= -

B=hij

Disk

A=abc D=mnp

C=tuv E=pq

Next:3.T2000 changesthevalueofDfrom“mnp”to“qrs”onpageP500?

P500PageLSN= 103

P600PageLSN= 102

P505PageLSN= -

P700PageLSN= -

B=klm


P600 102


101 - T1000 P500 Write A“abc” -> “def”

Update -

102 - T2000 P600 Write B“hij” -> “klm”

Update -

103 102 T2000 P500 Write D“mnp” -> “qrs”

Update -



T1000 101 Running

T2000 103 Running

Transaction table

Buffer Pool

30

A=def D=qrs

C=tuv E=pq

P500PageLSN= -

P600PageLSN= -

P505PageLSN= -

P700PageLSN= -

B=hij

Disk

A=abc D=mnp

C=tuv E=pq

Changes:3.T2000 changesthevalueofDfrom“mnp”to“qrs”onpageP500

P500PageLSN= 103

P600PageLSN= 102

P505PageLSN= -

P700PageLSN= -

B=klm


P600 102


101 - T1000 P500 Write A“abc” -> “def”

Update -

102 - T2000 P600 Write B“hij” -> “klm”

Update -

103 102 T2000 P500 Write D“mnp” -> “qrs”

Update -



T1000 101 Running

T2000 103 Running

Transaction table

Buffer Pool

31

A=def D=qrs

C=tuv E=pq

P500PageLSN= -

P600PageLSN= -

P505PageLSN= -

P700PageLSN= -

B=hij

Disk

A=abc D=mnp

C=tuv E=pq

Next:4.T1000 changesthevalueofCfrom“tuv”to“wxy”onpageP505?

P500PageLSN= 103

P600PageLSN= 102

P505PageLSN= 104

P700PageLSN= -

B=klm


P600 102

P505 104

LSN prevLSN

tID pID Log entry Type undoNextLSN

101 - T1000 P500 Write A“abc” -> “def”

Update -

102 - T2000 P600 Write B“hij” -> “klm”

Update -

103 102 T2000 P500 Write D“mnp” -> “qrs”

Update -

104 101 T1000 P505 Write C“tuv” -> “wxy”

Update -



T1000 104 Running

T2000 103 Running

Transaction table

Buffer Pool

32

A=defD=qrs

C=tuv E=pq

P500PageLSN= -

P600PageLSN= -

P505PageLSN= -

P700PageLSN= -

B=hij

Disk

A=abc D=mnp

C=tuv E=pq

Changes:4.T1000 changesthevalueofCfrom“tuv”to“wxy”onpageP505?

CSE 444: Database Internals - courses.cs.washington.edu · 2019-05-19 · Tk, or transactions that...

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Transcript of CSE 444: Database Internals - courses.cs.washington.edu · 2019-05-19 · Tk, or transactions that...