Distributed Systems Fundamentals for Databases | Chapter 8 – Database Internals

This chapter explores the fundamental transition from single-node programming to the complex landscape of distributed systems, highlighting how moving away from a single execution history introduces significant unpredictability. The discussion begins by distinguishing between concurrency, where multiple sequences of steps are in progress simultaneously but not necessarily executing at the same moment, and true parallelism, where operations occur simultaneously across multiple processors. A core focus is placed on the common fallacies of distributed computing, such as the dangerous assumptions that networks are always reliable, latency is zero, or bandwidth is infinite. The text details how these misconceptions lead to system failures, necessitating a deep understanding of processing delays, message queuing, and the importance of backpressure to prevent system overload. Furthermore, the chapter addresses the critical role of time and synchronization, explaining that without specialized hardware, local clocks inevitably drift, making it impossible to rely on simple timestamps for ordering events. To manage these challenges, various communication abstractions are defined, including fair-loss links that may drop messages and perfect links that ensure reliable, deduplicated delivery through the use of sequence numbers and acknowledgments. Theoretical constraints on system agreement are analyzed through the Two Generals' Problem and the FLP Impossibility result, which proves that reaching a consensus in a strictly asynchronous environment is impossible if even one process fails. The chapter concludes by categorizing failure models—ranging from simple crash-stop scenarios and message omissions to complex Byzantine faults where nodes act unpredictably—and emphasizes the necessity of building resilient architectures using tools like circuit breakers, retries with exponential backoff, and randomized jitter to maintain stability in the face of inevitable partial failures.


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