Timestamp-Ordering Concurrency Control Protocols

Lecture 34 introduces timestamp-ordering concurrency control as a deadlock-free alternative to locking-based protocols. In timestamp ordering, each transaction is assigned a monotonically increasing unique timestamp TS(T) at startup, establishing its serialization order in advance. Timestamps in distributed environments are generated using Lamport logical clocks combined with unique site identifiers. Each data item maintains a read timestamp R-TS(x) and write timestamp W-TS(x). The lecture details the Basic Timestamp Ordering (BTO) rules: a read operation is permitted if TS(T) >= W-TS(x); a write operation is permitted if TS(T) >= R-TS(x) and TS(T) >= W-TS(x). Operations violating these rules are rejected, and the issuing transaction is aborted and restarted. The Thomas Write Rule is evaluated, illustrating how obsolete write operations can be safely ignored without aborting. Atomic commitment protocols, notably Two-Phase Commit (2PC) and Three-Phase Commit (3PC), are demonstrated with formal state transition diagrams. Parallel database system architectures, spanning Shared-Memory, Shared-Disk, and Shared-Nothing topologies, are contrasted for speedup and scaleup performance. Parallel data placement techniques, including round-robin, hash partitioning, and range partitioning, illustrate workload balancing across processing nodes. Parallel join algorithms evaluate parallel nested-loop, associative, and parallel hash join executions in high-throughput query environments. Distributed Object-Oriented Database Management Systems (OODBMS) explore object identity, encapsulation, complex object hierarchies, and pointer swizzling. Client-server and page-server architectures in distributed OODBMS are analyzed for cache coherence, client caching, and transaction synchronization. Multidatabase and federated database systems illustrate how schema integration and mediation resolve semantic heterogeneity across legacy data stores. Exam preparation summaries and solved handout excerpts reinforce retention of critical mathematical proofs, fragmentation formulas, and execution algorithms. Comprehensive review of Virtual University exam patterns, past solved papers, and practice MCQs consolidates theoretical mastery and practical design competence. Systematic preparation on VU SIGMA empowers students to achieve outstanding grades in university examinations through structured practice and verified feedback. In this lecture, students examine fundamental architectural principles and engineering protocols governing distributed database management systems. Through systematic technical analyses, the lesson explores data distribution strategies, network communication latency, and autonomous local site processing.