Older transaction waits for younger, younger dies. Wound-Wait: Older transaction "wounds" (preempts) younger. 4. Reliability and the Two-Phase Commit (2PC)
Most structural exam questions ask you to trace the message history of a Two-Phase Commit protocol under normal operation or node failure.
Distributed query optimization minimizes communication costs (data transfer over the network), local CPU costs, and I/O costs. Exercise: Join Strategies and Semijoin Optimization Relation resides at Site 1 with 1,000 tuples. Relation Older transaction waits for younger, younger dies
Data fragmentation splits a global database relation into smaller logical pieces (fragments) stored across different network nodes. Exercises in this domain typically test your ability to execute horizontal or vertical fragmentation without losing data integrity. Horizontal Fragmentation (Primary & Derived)
Exercise Write-up: Principles of Distributed Database Systems Reliability and the Two-Phase Commit (2PC) Most structural
Primary horizontal fragmentation divides a relation based on predicates run against its own attributes. Derived horizontal fragmentation divides a relation based on predicates applied to a different relation.
Cost1=50 unique values×4 bytes=200 bytesCost sub 1 equals 50 unique values cross 4 bytes equals 200 bytes had promised convergence. Reality
Consider a relation Employees (EmpID, Name, Dept, Salary, Location) .
"Not tonight," she whispered, kneading her temples. The exercise was simple in theory: execute a series of atomic transactions that moved virtual currency between accounts while maintaining ACID properties across the network. The solution, the beautiful theoretical proof on her whiteboard, had promised convergence. Reality, as always, had other plans.
Calculate based on data transfer sizes and site communication delays.
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