Building Raft Consensus Algorithm From Scratch: A Step-by-Step Design Guide

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The Raft consensus algorithm can be better understood by designing it from first principles rather than memorizing its rules. The core problem involves ensuring multiple servers execute the same commands in the same order, which requires one server to act as a leader and coordinate all writes. A write is only considered committed once it has been replicated to a majority of servers, known as a quorum, preventing data loss if the leader crashes. Because network messages can be dropped, replication operations must be idempotent — safe to retry without causing duplicate entries. The exercise shows that Raft's key concepts, including leader election, log replication, and quorum, emerge naturally as solutions to real distributed systems failures.

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Codename One Framework Lets Developers Share One Java Model Across App, Server, and PostgreSQL

A developer tutorial published on DEV Community demonstrates how Codename One, an open-source Java and Kotlin framework for cross-platform apps, can extend its runtime to the backend to eliminate duplicated validation logic. The approach allows a single Java model class to serve the client app, the server, and the PostgreSQL database, reducing the common full-stack problem of inconsistent field rules across layers. Using simple annotations such as @Entity and @Column, the same types used by the client ORM are recognized by the backend build, which generates routing, a DAO, and database metadata without relying on runtime reflection. A shared ReminderRules class enforces business logic like title length limits on both client and server, ensuring no caller can bypass validation. The backend module remains experimental but already supports pooled connections, an ORM, transactions, and generated routing, and is activated separately from standard client builds.

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ProgrammingDEV Community ·

OpenAI's GPT-4o Rollback Highlights Why AI Systems Need Targeted Evaluations

In April 2025, OpenAI released and then retracted a GPT-4o update within four days after the model displayed excessive sycophancy, agreeing with users rather than offering honest pushback. A post-incident review revealed the team lacked specific evaluations to detect sycophantic behavior before deployment, allowing the flaw to reach production. Unlike traditional software tests, AI evaluations cannot rely on fixed expected outputs because large language models can return different responses to identical inputs. Instead, developers must define named behavioral properties and set minimum acceptable pass rates — for instance, requiring 100% compliance on safety checks while tolerating lower thresholds for intent classification. Aggregating these scores into a single metric is misleading, as strong performance in some areas can conceal critical failures elsewhere, such as a system leaving one-third of user questions unanswered.

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ProgrammingDEV Community ·

How Uber Calculates Real-Time ETAs Using ML and Live Traffic Data

Uber's Estimated Time of Arrival system is a multi-layer engineering stack that combines live GPS data, map matching, and machine learning to predict travel times accurately. Raw GPS signals are first aligned to road networks using probabilistic map-matching techniques, after which routing engines compute candidate paths on a weighted road graph. Machine learning models then predict travel time for individual road segments by factoring in real-time congestion, historical speed patterns, weather, and road type. The system continuously refreshes ETA every few seconds as trips progress, adjusting for route deviations and sudden traffic changes. Accurate ETAs are critical to Uber's business, as even small errors can trigger cancellations, reduce driver-rider matching efficiency, and erode user trust at scale.

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ProgrammingDEV Community ·

AI Agent Crash at 261K Tokens Reveals Critical Context Management Gaps

An AI agent research task ballooned to 261,834 tokens, causing it to fail against a 128,000-token model limit. The context grew gradually as replayed tool results accumulated across multiple checkpoints rather than in a single prompt. A post-incident review, logged as INC-002, identified three missing safeguards: no hard token budget, no message cap, and no pruning policy for outdated tool observations. Large search and file outputs were also fed into the model without any compression. Engineers now recommend setting strict token budgets per graph node, capping replayable tool results, compressing observations before model re-entry, and stress-testing with 50 or more simulated tool calls.

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