Vossen-Book-ch3

Database Management Systems

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02/26/10 Transactional Information Systems 3-1 Part II: Concurrency Control 3 Concurrency Control: Notions of Correctness for the Page Model 4 Concurrency Control Algorithms 5 Multiversion Concurrency Control 6 Concurrency Control on Objects: Notions of Correctness 7 Concurrency Control Algorithms on Objects 8 Concurrency Control on Relational Databases 9 Concurrency Control on Search Structures 10 Implementation and Pragmatic Issues
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02/26/10 Transactional Information Systems 3-2 Chapter 3: Concurrency Control – Notions of Correctness for the Page Model 3.2 Canonical Synchronization Problems 3.3 Syntax of Histories and Schedules 3.4 Correctness of Histories and Schedules 3.5 Herbrand Semantics of Schedules 3.6 Final-State Serializability 3.7 View Serializability 3.8 Conflict Serializability 3.9 Commit Serializability 3.10 An Alternative Criterion: Interleaving Specifications 3.11 Lessons Learned “Nothing is as practical as a good theory.” (Albert Einstein)
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02/26/10 Transactional Information Systems 3-3 Lost Update Problem P1 Time P2 /* x = 100 */ r (x) 1 2 r (x) x := x+100 4 x := x+200 w (x) 5 /* x = 200 */ 6 w (x) /* x = 300 */ update “lost” Observation: problem is the interleaving r 1 (x) r 2 (x) w 1 (x) w 2 (x) Example 3.1
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02/26/10 Transactional Information Systems 3-4 Inconsistent Read Problem P1 Time P2 1 r (x) 2 x := x – 10 3 w (x) sum := 0 4 r (x) 5 r (y) 6 sum := sum +x 7 sum := sum + y 8 9 r (y) 10 y := y + 10 11 w (y) “sees” wrong sum Observations: problem is the interleaving r 2 (x) w 2 (x) r 1 (x) r 1 (y) r 2 (y) w 2 (y) Example 3.2
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02/26/10 Transactional Information Systems 3-5 Dirty Read Problem P1 Time P2 r (x) 1 x := x + 100 2 w (x) 3 4 r (x) 5 x := x - 100 failure & rollback 6 7 w (x) cannot rely on validity of previously read data Observation: transaction rollbacks could affect concurrent transactions Example 3.3
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02/26/10 Transactional Information Systems 3-6 Chapter 3: Concurrency Control – Notions of Correctness for the Page Model 3.2 Canonical Synchronization Problems 3.3 Syntax of Histories and Schedules 3.4 Correctness of Histories and Schedules 3.5 Herbrand Semantics of Schedules 3.6 Final-State Serializability 3.7 View Serializability 3.8 Conflict Serializability 3.9 Commit Serializability 3.10 An Alternative Criterion: Interleaving Specifications 3.11 Lessons Learned
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02/26/10 Transactional Information Systems 3-7 Schedules and Histories Definition 3.1 (Schedules and histories): Let T={t 1 , . .., t n } be a set of transactions, where each t i T has the form t i =(op i , < i ) with op i denoting the operations of t i and < i their ordering. (i) A history for T is a pair s=(op(s),< s ) s.t. (a) op(s) i=1. .n op i i=1. .n {a i , c i } (b) for all i, 1 i n: c i op(s) a i op(s) (c) i=1. .n < i < s (d) for all i, 1 i n, and all p op i : p < s c i or p < s a i (e) for all p, q op(s) s.t. at least one of them is a write and both access the same data item: p < s q or q < s p (ii) A schedule is a prefix of a history.
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Vossen-Book-ch3 - Part II: Concurrency Control 3...

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