# ch11-1 - Chapter 11 Distributed Concurrency Control Chapter...

This preview shows pages 1–4. Sign up to view the full content.

Chapter 11 Distributed Concurrency Control Chapter 11 Distributed Concurrency Control Concurrency control ensures the consistency and reliability properties of transactions. 111 SERIALIZABILITY THEORY The most widely accepted correctness criterion for concurrency control algorithms. A schedule S (also called history ) is defined over a set of transactions T={T1, T2, …,Tn} and specifies order of execution of these transactions’ operations. Two operations O x ij ( ) and O x kl ( ) accessing the same data item x are in conflict if one of them is a write. Conflicts are divided into r ead-write ( or write-read ) and write-write types. Two transactions are in conflict if an operation of one transaction is in conflict with an operation of the other by above definition. A complete schedule S T C defined over a set of transactions T={T1,T2,…,Tn} is a partial order 1

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Chapter 11 Distributed Concurrency Control S T C T T = { , } h where 1. = ∪ = i n i T 1 2. i n i T c c 1 = 3. For any two conflicting operations O x ij ( ) and O x kl ( ) inΣ T , either O x ij ( ) h T O x kl ( ) , or O x kl ( ) h T O x ij ( ) . The last condition defines the execution order among conflicting operations. Example: find a complete schedule for two transactions T 1 and T 2 T 1 T 2 time Read(x) Read(x) x x+1 x x+1 Write(x) Write(x) Commit Commit = 1 ∪∑ 2 ={R 1 (x),W 1 (x),C 1 ,R 2 (x),W 2 (x),C 2 } DAG representation of one possible complete schedule. 2
Chapter 11 Distributed Concurrency Control R 1 (x) R 2 (x) W 1 (x) W 2 (x) C 1 C 2 Note the dashed lines are added to make the schedule complete. The complete schedule can be simplified by { R 1 (x),R 2 (x),W 1 (x),C 1 ,W 2 (x),C 2 } that specifies all operations of T1 and T2 and their relative orders. A schedule is a prefix of a complete schedule. A

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 14

ch11-1 - Chapter 11 Distributed Concurrency Control Chapter...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online