SlideShare une entreprise Scribd logo
1  sur  21
Crash Recovery ,[object Object],[object Object],[object Object],[object Object],[object Object]
Logging ,[object Object],[object Object],[object Object],[object Object],[object Object]
Introduction to ARIES ,[object Object],[object Object],[object Object],[object Object]
No force and Steal approach
ARIES  contd… . ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
ARIES Recovery Algorithm ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Write-Ahead Logging (WAL) ,[object Object],[object Object],[object Object],[object Object],[object Object]
WAL & the Log ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
The log ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Log record with actions ,[object Object],[object Object],[object Object],[object Object],[object Object]
Update log Record & Compensation Log Record(CLR) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Other Recovery Related Structure ,[object Object],[object Object],[object Object],[object Object],[object Object]
Write ahead log protocol ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Checkpointing ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Checkpointing ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Fuzzy checkpointing… ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Some more notes on checkpointing.. ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Recovering from system crash ,[object Object],[object Object],[object Object],[object Object],[object Object]
Analysis phase ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Redo phase ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Undo phase ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Contenu connexe

Tendances

Database recovery techniques
Database recovery techniquesDatabase recovery techniques
Database recovery techniquespusp220
 
Transactions in dbms
Transactions in dbmsTransactions in dbms
Transactions in dbmsNancy Gulati
 
Transaction Management
Transaction Management Transaction Management
Transaction Management Visakh V
 
DBMS-chap 2-Concurrency Control
DBMS-chap 2-Concurrency ControlDBMS-chap 2-Concurrency Control
DBMS-chap 2-Concurrency ControlMukesh Tekwani
 
Transaction slide
Transaction slideTransaction slide
Transaction slideshawon roy
 
15. Transactions in DBMS
15. Transactions in DBMS15. Transactions in DBMS
15. Transactions in DBMSkoolkampus
 
Dbms sixth chapter_part-1_2011
Dbms sixth chapter_part-1_2011Dbms sixth chapter_part-1_2011
Dbms sixth chapter_part-1_2011sumit_study
 
Transaction states and properties
Transaction states and propertiesTransaction states and properties
Transaction states and propertiesChetan Mahawar
 
Dbms recovering from a system crash
Dbms recovering from a system crashDbms recovering from a system crash
Dbms recovering from a system crashAbhishek Kumar Gupta
 
Lesson12 recovery architectures
Lesson12 recovery architecturesLesson12 recovery architectures
Lesson12 recovery architecturesRaval Vijay
 
Introduction to database-Transaction Concurrency and Recovery
Introduction to database-Transaction Concurrency and RecoveryIntroduction to database-Transaction Concurrency and Recovery
Introduction to database-Transaction Concurrency and RecoveryAjit Nayak
 

Tendances (20)

Tybsc cs dbms2 notes
Tybsc cs dbms2 notesTybsc cs dbms2 notes
Tybsc cs dbms2 notes
 
DBMS - Transactions
DBMS - TransactionsDBMS - Transactions
DBMS - Transactions
 
Database recovery techniques
Database recovery techniquesDatabase recovery techniques
Database recovery techniques
 
Transactions in dbms
Transactions in dbmsTransactions in dbms
Transactions in dbms
 
Transaction Management
Transaction Management Transaction Management
Transaction Management
 
DBMS-chap 2-Concurrency Control
DBMS-chap 2-Concurrency ControlDBMS-chap 2-Concurrency Control
DBMS-chap 2-Concurrency Control
 
Transaction slide
Transaction slideTransaction slide
Transaction slide
 
Transaction processing
Transaction processingTransaction processing
Transaction processing
 
Unit07 dbms
Unit07 dbmsUnit07 dbms
Unit07 dbms
 
Concurrency
ConcurrencyConcurrency
Concurrency
 
15. Transactions in DBMS
15. Transactions in DBMS15. Transactions in DBMS
15. Transactions in DBMS
 
Ch15 3717
Ch15 3717Ch15 3717
Ch15 3717
 
Dbms sixth chapter_part-1_2011
Dbms sixth chapter_part-1_2011Dbms sixth chapter_part-1_2011
Dbms sixth chapter_part-1_2011
 
Transaction states and properties
Transaction states and propertiesTransaction states and properties
Transaction states and properties
 
Ch15
Ch15Ch15
Ch15
 
Lec08
Lec08Lec08
Lec08
 
Dbms recovering from a system crash
Dbms recovering from a system crashDbms recovering from a system crash
Dbms recovering from a system crash
 
24904 lecture11
24904 lecture1124904 lecture11
24904 lecture11
 
Lesson12 recovery architectures
Lesson12 recovery architecturesLesson12 recovery architectures
Lesson12 recovery architectures
 
Introduction to database-Transaction Concurrency and Recovery
Introduction to database-Transaction Concurrency and RecoveryIntroduction to database-Transaction Concurrency and Recovery
Introduction to database-Transaction Concurrency and Recovery
 

En vedette

Transaction unit1 topic 2
Transaction unit1 topic 2Transaction unit1 topic 2
Transaction unit1 topic 2avniS
 
Locks with updt nowait
Locks with updt nowaitLocks with updt nowait
Locks with updt nowaitavniS
 
12c for Developers - Feb 2014
12c for Developers - Feb 201412c for Developers - Feb 2014
12c for Developers - Feb 2014Connor McDonald
 
Buffer management --database buffering
Buffer management --database buffering Buffer management --database buffering
Buffer management --database buffering julia121214
 
Locking unit 1 topic 3
Locking unit 1 topic 3Locking unit 1 topic 3
Locking unit 1 topic 3avniS
 
Troubleshooting Complex Performance issues - Oracle SEG$ contention
Troubleshooting Complex Performance issues - Oracle SEG$ contentionTroubleshooting Complex Performance issues - Oracle SEG$ contention
Troubleshooting Complex Performance issues - Oracle SEG$ contentionTanel Poder
 
JPD1405 Distributed, Concurrent, and Independent Access to Encrypted Cloud D...
JPD1405  Distributed, Concurrent, and Independent Access to Encrypted Cloud D...JPD1405  Distributed, Concurrent, and Independent Access to Encrypted Cloud D...
JPD1405 Distributed, Concurrent, and Independent Access to Encrypted Cloud D...chennaijp
 
Distributed, concurrent, and independent access to encrypted cloud databases
Distributed, concurrent, and independent access to encrypted cloud databasesDistributed, concurrent, and independent access to encrypted cloud databases
Distributed, concurrent, and independent access to encrypted cloud databasesPapitha Velumani
 
17. Recovery System in DBMS
17. Recovery System in DBMS17. Recovery System in DBMS
17. Recovery System in DBMSkoolkampus
 
分区表基础知识培训
分区表基础知识培训分区表基础知识培训
分区表基础知识培训maclean liu
 
Transaction concurrency control
Transaction concurrency controlTransaction concurrency control
Transaction concurrency controlAnand Grewal
 
Transaction management
Transaction managementTransaction management
Transaction managementrenuka_a
 
Database management system
Database management systemDatabase management system
Database management systemRizwanHafeez
 
Database management system presentation
Database management system presentationDatabase management system presentation
Database management system presentationsameerraaj
 

En vedette (17)

Transaction unit1 topic 2
Transaction unit1 topic 2Transaction unit1 topic 2
Transaction unit1 topic 2
 
Locks with updt nowait
Locks with updt nowaitLocks with updt nowait
Locks with updt nowait
 
12c for Developers - Feb 2014
12c for Developers - Feb 201412c for Developers - Feb 2014
12c for Developers - Feb 2014
 
Buffer management --database buffering
Buffer management --database buffering Buffer management --database buffering
Buffer management --database buffering
 
Locking unit 1 topic 3
Locking unit 1 topic 3Locking unit 1 topic 3
Locking unit 1 topic 3
 
Troubleshooting Complex Performance issues - Oracle SEG$ contention
Troubleshooting Complex Performance issues - Oracle SEG$ contentionTroubleshooting Complex Performance issues - Oracle SEG$ contention
Troubleshooting Complex Performance issues - Oracle SEG$ contention
 
JPD1405 Distributed, Concurrent, and Independent Access to Encrypted Cloud D...
JPD1405  Distributed, Concurrent, and Independent Access to Encrypted Cloud D...JPD1405  Distributed, Concurrent, and Independent Access to Encrypted Cloud D...
JPD1405 Distributed, Concurrent, and Independent Access to Encrypted Cloud D...
 
Distributed, concurrent, and independent access to encrypted cloud databases
Distributed, concurrent, and independent access to encrypted cloud databasesDistributed, concurrent, and independent access to encrypted cloud databases
Distributed, concurrent, and independent access to encrypted cloud databases
 
17. Recovery System in DBMS
17. Recovery System in DBMS17. Recovery System in DBMS
17. Recovery System in DBMS
 
分区表基础知识培训
分区表基础知识培训分区表基础知识培训
分区表基础知识培训
 
Transaction concurrency control
Transaction concurrency controlTransaction concurrency control
Transaction concurrency control
 
Transaction management
Transaction managementTransaction management
Transaction management
 
Database management system
Database management systemDatabase management system
Database management system
 
Data Base Management System
Data Base Management SystemData Base Management System
Data Base Management System
 
Basic DBMS ppt
Basic DBMS pptBasic DBMS ppt
Basic DBMS ppt
 
Dbms slides
Dbms slidesDbms slides
Dbms slides
 
Database management system presentation
Database management system presentationDatabase management system presentation
Database management system presentation
 

Similaire à Transaction unit 1 topic 4

CS 542 -- Failure Recovery, Concurrency Control
CS 542 -- Failure Recovery, Concurrency ControlCS 542 -- Failure Recovery, Concurrency Control
CS 542 -- Failure Recovery, Concurrency ControlJ Singh
 
Sql server lesson10
Sql server lesson10Sql server lesson10
Sql server lesson10Ala Qunaibi
 
recovery system
recovery systemrecovery system
recovery systemshreeuva
 
Recovery System.pptx
Recovery System.pptxRecovery System.pptx
Recovery System.pptxssuserfb9a21
 
Transactionsmanagement
TransactionsmanagementTransactionsmanagement
TransactionsmanagementSanjeev Gupta
 
UNIT 4- CRASH AND RECOVERY.pdf
UNIT 4- CRASH AND RECOVERY.pdfUNIT 4- CRASH AND RECOVERY.pdf
UNIT 4- CRASH AND RECOVERY.pdfKavitaShinde26
 
Introduction to transaction processing concepts and theory
Introduction to transaction processing concepts and theoryIntroduction to transaction processing concepts and theory
Introduction to transaction processing concepts and theoryZainab Almugbel
 
ch 5 Daatabase Recovery.ppt
ch 5 Daatabase Recovery.pptch 5 Daatabase Recovery.ppt
ch 5 Daatabase Recovery.pptAdemeCheklie
 
Relational Database Management System
Relational Database Management SystemRelational Database Management System
Relational Database Management Systemsweetysweety8
 
Adbms 34 transaction processing and recovery
Adbms 34 transaction processing and recoveryAdbms 34 transaction processing and recovery
Adbms 34 transaction processing and recoveryVaibhav Khanna
 

Similaire à Transaction unit 1 topic 4 (20)

Aries
AriesAries
Aries
 
Chapter19
Chapter19Chapter19
Chapter19
 
CS 542 -- Failure Recovery, Concurrency Control
CS 542 -- Failure Recovery, Concurrency ControlCS 542 -- Failure Recovery, Concurrency Control
CS 542 -- Failure Recovery, Concurrency Control
 
Sql server lesson10
Sql server lesson10Sql server lesson10
Sql server lesson10
 
recovery system
recovery systemrecovery system
recovery system
 
Recovery System.pptx
Recovery System.pptxRecovery System.pptx
Recovery System.pptx
 
Transactionsmanagement
TransactionsmanagementTransactionsmanagement
Transactionsmanagement
 
Dbms
DbmsDbms
Dbms
 
UNIT 4- CRASH AND RECOVERY.pdf
UNIT 4- CRASH AND RECOVERY.pdfUNIT 4- CRASH AND RECOVERY.pdf
UNIT 4- CRASH AND RECOVERY.pdf
 
Aries
AriesAries
Aries
 
Aries
AriesAries
Aries
 
Aries
AriesAries
Aries
 
Write behind logging
Write behind loggingWrite behind logging
Write behind logging
 
Introduction to transaction processing concepts and theory
Introduction to transaction processing concepts and theoryIntroduction to transaction processing concepts and theory
Introduction to transaction processing concepts and theory
 
ch 5 Daatabase Recovery.ppt
ch 5 Daatabase Recovery.pptch 5 Daatabase Recovery.ppt
ch 5 Daatabase Recovery.ppt
 
Data (1)
Data (1)Data (1)
Data (1)
 
DBMS Vardhaman.pdf
DBMS Vardhaman.pdfDBMS Vardhaman.pdf
DBMS Vardhaman.pdf
 
Assignment#14
Assignment#14Assignment#14
Assignment#14
 
Relational Database Management System
Relational Database Management SystemRelational Database Management System
Relational Database Management System
 
Adbms 34 transaction processing and recovery
Adbms 34 transaction processing and recoveryAdbms 34 transaction processing and recovery
Adbms 34 transaction processing and recovery
 

Dernier

Unraveling Multimodality with Large Language Models.pdf
Unraveling Multimodality with Large Language Models.pdfUnraveling Multimodality with Large Language Models.pdf
Unraveling Multimodality with Large Language Models.pdfAlex Barbosa Coqueiro
 
"Subclassing and Composition – A Pythonic Tour of Trade-Offs", Hynek Schlawack
"Subclassing and Composition – A Pythonic Tour of Trade-Offs", Hynek Schlawack"Subclassing and Composition – A Pythonic Tour of Trade-Offs", Hynek Schlawack
"Subclassing and Composition – A Pythonic Tour of Trade-Offs", Hynek SchlawackFwdays
 
Vector Databases 101 - An introduction to the world of Vector Databases
Vector Databases 101 - An introduction to the world of Vector DatabasesVector Databases 101 - An introduction to the world of Vector Databases
Vector Databases 101 - An introduction to the world of Vector DatabasesZilliz
 
Unleash Your Potential - Namagunga Girls Coding Club
Unleash Your Potential - Namagunga Girls Coding ClubUnleash Your Potential - Namagunga Girls Coding Club
Unleash Your Potential - Namagunga Girls Coding ClubKalema Edgar
 
Nell’iperspazio con Rocket: il Framework Web di Rust!
Nell’iperspazio con Rocket: il Framework Web di Rust!Nell’iperspazio con Rocket: il Framework Web di Rust!
Nell’iperspazio con Rocket: il Framework Web di Rust!Commit University
 
Designing IA for AI - Information Architecture Conference 2024
Designing IA for AI - Information Architecture Conference 2024Designing IA for AI - Information Architecture Conference 2024
Designing IA for AI - Information Architecture Conference 2024Enterprise Knowledge
 
Kotlin Multiplatform & Compose Multiplatform - Starter kit for pragmatics
Kotlin Multiplatform & Compose Multiplatform - Starter kit for pragmaticsKotlin Multiplatform & Compose Multiplatform - Starter kit for pragmatics
Kotlin Multiplatform & Compose Multiplatform - Starter kit for pragmaticscarlostorres15106
 
Search Engine Optimization SEO PDF for 2024.pdf
Search Engine Optimization SEO PDF for 2024.pdfSearch Engine Optimization SEO PDF for 2024.pdf
Search Engine Optimization SEO PDF for 2024.pdfRankYa
 
"ML in Production",Oleksandr Bagan
"ML in Production",Oleksandr Bagan"ML in Production",Oleksandr Bagan
"ML in Production",Oleksandr BaganFwdays
 
AI as an Interface for Commercial Buildings
AI as an Interface for Commercial BuildingsAI as an Interface for Commercial Buildings
AI as an Interface for Commercial BuildingsMemoori
 
Ensuring Technical Readiness For Copilot in Microsoft 365
Ensuring Technical Readiness For Copilot in Microsoft 365Ensuring Technical Readiness For Copilot in Microsoft 365
Ensuring Technical Readiness For Copilot in Microsoft 3652toLead Limited
 
Human Factors of XR: Using Human Factors to Design XR Systems
Human Factors of XR: Using Human Factors to Design XR SystemsHuman Factors of XR: Using Human Factors to Design XR Systems
Human Factors of XR: Using Human Factors to Design XR SystemsMark Billinghurst
 
My INSURER PTE LTD - Insurtech Innovation Award 2024
My INSURER PTE LTD - Insurtech Innovation Award 2024My INSURER PTE LTD - Insurtech Innovation Award 2024
My INSURER PTE LTD - Insurtech Innovation Award 2024The Digital Insurer
 
Streamlining Python Development: A Guide to a Modern Project Setup
Streamlining Python Development: A Guide to a Modern Project SetupStreamlining Python Development: A Guide to a Modern Project Setup
Streamlining Python Development: A Guide to a Modern Project SetupFlorian Wilhelm
 
Connect Wave/ connectwave Pitch Deck Presentation
Connect Wave/ connectwave Pitch Deck PresentationConnect Wave/ connectwave Pitch Deck Presentation
Connect Wave/ connectwave Pitch Deck PresentationSlibray Presentation
 
Are Multi-Cloud and Serverless Good or Bad?
Are Multi-Cloud and Serverless Good or Bad?Are Multi-Cloud and Serverless Good or Bad?
Are Multi-Cloud and Serverless Good or Bad?Mattias Andersson
 
"LLMs for Python Engineers: Advanced Data Analysis and Semantic Kernel",Oleks...
"LLMs for Python Engineers: Advanced Data Analysis and Semantic Kernel",Oleks..."LLMs for Python Engineers: Advanced Data Analysis and Semantic Kernel",Oleks...
"LLMs for Python Engineers: Advanced Data Analysis and Semantic Kernel",Oleks...Fwdays
 
What's New in Teams Calling, Meetings and Devices March 2024
What's New in Teams Calling, Meetings and Devices March 2024What's New in Teams Calling, Meetings and Devices March 2024
What's New in Teams Calling, Meetings and Devices March 2024Stephanie Beckett
 
Story boards and shot lists for my a level piece
Story boards and shot lists for my a level pieceStory boards and shot lists for my a level piece
Story boards and shot lists for my a level piececharlottematthew16
 

Dernier (20)

Unraveling Multimodality with Large Language Models.pdf
Unraveling Multimodality with Large Language Models.pdfUnraveling Multimodality with Large Language Models.pdf
Unraveling Multimodality with Large Language Models.pdf
 
"Subclassing and Composition – A Pythonic Tour of Trade-Offs", Hynek Schlawack
"Subclassing and Composition – A Pythonic Tour of Trade-Offs", Hynek Schlawack"Subclassing and Composition – A Pythonic Tour of Trade-Offs", Hynek Schlawack
"Subclassing and Composition – A Pythonic Tour of Trade-Offs", Hynek Schlawack
 
Vector Databases 101 - An introduction to the world of Vector Databases
Vector Databases 101 - An introduction to the world of Vector DatabasesVector Databases 101 - An introduction to the world of Vector Databases
Vector Databases 101 - An introduction to the world of Vector Databases
 
Unleash Your Potential - Namagunga Girls Coding Club
Unleash Your Potential - Namagunga Girls Coding ClubUnleash Your Potential - Namagunga Girls Coding Club
Unleash Your Potential - Namagunga Girls Coding Club
 
Nell’iperspazio con Rocket: il Framework Web di Rust!
Nell’iperspazio con Rocket: il Framework Web di Rust!Nell’iperspazio con Rocket: il Framework Web di Rust!
Nell’iperspazio con Rocket: il Framework Web di Rust!
 
Designing IA for AI - Information Architecture Conference 2024
Designing IA for AI - Information Architecture Conference 2024Designing IA for AI - Information Architecture Conference 2024
Designing IA for AI - Information Architecture Conference 2024
 
Kotlin Multiplatform & Compose Multiplatform - Starter kit for pragmatics
Kotlin Multiplatform & Compose Multiplatform - Starter kit for pragmaticsKotlin Multiplatform & Compose Multiplatform - Starter kit for pragmatics
Kotlin Multiplatform & Compose Multiplatform - Starter kit for pragmatics
 
Search Engine Optimization SEO PDF for 2024.pdf
Search Engine Optimization SEO PDF for 2024.pdfSearch Engine Optimization SEO PDF for 2024.pdf
Search Engine Optimization SEO PDF for 2024.pdf
 
"ML in Production",Oleksandr Bagan
"ML in Production",Oleksandr Bagan"ML in Production",Oleksandr Bagan
"ML in Production",Oleksandr Bagan
 
E-Vehicle_Hacking_by_Parul Sharma_null_owasp.pptx
E-Vehicle_Hacking_by_Parul Sharma_null_owasp.pptxE-Vehicle_Hacking_by_Parul Sharma_null_owasp.pptx
E-Vehicle_Hacking_by_Parul Sharma_null_owasp.pptx
 
AI as an Interface for Commercial Buildings
AI as an Interface for Commercial BuildingsAI as an Interface for Commercial Buildings
AI as an Interface for Commercial Buildings
 
Ensuring Technical Readiness For Copilot in Microsoft 365
Ensuring Technical Readiness For Copilot in Microsoft 365Ensuring Technical Readiness For Copilot in Microsoft 365
Ensuring Technical Readiness For Copilot in Microsoft 365
 
Human Factors of XR: Using Human Factors to Design XR Systems
Human Factors of XR: Using Human Factors to Design XR SystemsHuman Factors of XR: Using Human Factors to Design XR Systems
Human Factors of XR: Using Human Factors to Design XR Systems
 
My INSURER PTE LTD - Insurtech Innovation Award 2024
My INSURER PTE LTD - Insurtech Innovation Award 2024My INSURER PTE LTD - Insurtech Innovation Award 2024
My INSURER PTE LTD - Insurtech Innovation Award 2024
 
Streamlining Python Development: A Guide to a Modern Project Setup
Streamlining Python Development: A Guide to a Modern Project SetupStreamlining Python Development: A Guide to a Modern Project Setup
Streamlining Python Development: A Guide to a Modern Project Setup
 
Connect Wave/ connectwave Pitch Deck Presentation
Connect Wave/ connectwave Pitch Deck PresentationConnect Wave/ connectwave Pitch Deck Presentation
Connect Wave/ connectwave Pitch Deck Presentation
 
Are Multi-Cloud and Serverless Good or Bad?
Are Multi-Cloud and Serverless Good or Bad?Are Multi-Cloud and Serverless Good or Bad?
Are Multi-Cloud and Serverless Good or Bad?
 
"LLMs for Python Engineers: Advanced Data Analysis and Semantic Kernel",Oleks...
"LLMs for Python Engineers: Advanced Data Analysis and Semantic Kernel",Oleks..."LLMs for Python Engineers: Advanced Data Analysis and Semantic Kernel",Oleks...
"LLMs for Python Engineers: Advanced Data Analysis and Semantic Kernel",Oleks...
 
What's New in Teams Calling, Meetings and Devices March 2024
What's New in Teams Calling, Meetings and Devices March 2024What's New in Teams Calling, Meetings and Devices March 2024
What's New in Teams Calling, Meetings and Devices March 2024
 
Story boards and shot lists for my a level piece
Story boards and shot lists for my a level pieceStory boards and shot lists for my a level piece
Story boards and shot lists for my a level piece
 

Transaction unit 1 topic 4

  • 1.
  • 2.
  • 3.
  • 4. No force and Steal approach
  • 5.
  • 6.
  • 7.
  • 8.
  • 9.
  • 10.
  • 11.
  • 12.
  • 13.
  • 14.
  • 15.
  • 16.
  • 17.
  • 18.
  • 19.
  • 20.
  • 21.