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Introduction 1. Introduction 1 Roles of Transactions Thomas Leich Transaction Management Last updated: 11.11.2016 1–1 Introduction 1. Introduction 1 Roles of Transactions 2 Transactions in the Architecture of a DBMS Thomas Leich Transaction Management Last updated: 11.11.2016 1–1 Introduction Roles of Transactions Nine capabilities of a DBMS by Codd 1 Integration 2 Operations 3 Catalog 4 Views 5 Consistency Control 6 Data Protection 7 Transactions 8 Synchronization 9 Recovery Thomas Leich Transaction Management Last updated: 11.11.2016 1–2 Introduction Roles of Transactions Transaction properties A transaction is a sequence of operations (actions), which transfers a database from a consistent state into another eventually changed consistent state, applying the ACID properties. Aspects: I I Semantic integrity: Correct (consistent) database state after the end of transactions run-time integrity: Avoid errors caused by simultaneous access of several users to the same data Thomas Leich Transaction Management Last updated: 11.11.2016 1–3 Introduction Roles of Transactions ACID Properties Atomicity: Transactions are either completed, or not performed at all. Consistency: If the database is in a consistent state before a transaction starts, the database is also consistent after the transaction has ended. Isolation: A user who is working on the database should not notice any other user working on it. Durability: The result of a transaction must be permanently stored within the database, after the transaction is completed. Thomas Leich Transaction Management Last updated: 11.11.2016 1–4 Introduction Transactions in the Architecture of a DBMS Architecture of DBMS Set−Oriented Interface (SOI) Data System Translation, Acces Path Selection, Access Control, Integrity Control Record−Oriented Interface (ROI) Access System Data Dictionary, Currency Pointer, Sorting, Concurrency Control Storage System Record Manager, Access Path Management, Lock Management, Log/Recovery Internal Record Interface (IRI) System Buffer Interface (SBI) Buffer Management System Buffer Management with Page Replace Strategy Operating System External Storage Management File Interface (FI) Device Interface (DI) Thomas Leich Transaction Management Last updated: 11.11.2016 1–5 Introduction Transactions in the Architecture of a DBMS Storage hierarchy Cache Primary Storage Main Memory Disk Memory Secondary Storage Optical Disk Tertiary Storage Magnetic Tapes Thomas Leich Transaction Management Last updated: 11.11.2016 1–6