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Tutorials, Errors and Exceptions
Its a journey to understand things better. It will have tutorials, any error/exceptions encountered, its resolutions and lots of learning.

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Real-Time Aggregations with Kafka Streams at 10K Events/Sec
Part 3 of the StreamMetrics Series Previous parts: Part 1: Kafka Producer | Part 2: Consumer + DLQ | Part 4: From Localhost to Kubernetes Building production-grade streaming analytics: windows, state stores, and performance validation Overview In Parts 1 and 2, we built a Kafka producer and consumer that process individual events reliably. But processing 10,000 raw events per second creates a new problem: How do you extract insights from that fire hose of data? Enter Kafka
Ankit Agrahari
Feb 217 min read
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Building Production-Grade Apache Kafka Consumer Patterns
Part 2 of the StreamMetrics Series Previous parts: Part 1: Kafka Producer | Part 3: Real-time Aggregation | Part 4: From Localhost to Kubernetes A deep-dive into manual offset management, dead letter queues, and observability with Spring Boot + Apache Kafka. This is part 2 of the series Stream Metrics application. In Part 1 we built the producer, today we add the consumer. Why This Matters Most tutorials show you how to build a Kafka consumer. They show you @KafkaListener
Ankit Agrahari
Feb 186 min read
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Building a Production Kafka Producer
Part 1 of the StreamMetrics Series Previous parts: Part 2: Consumer + DLQ | Part 3: Real-Time Aggregations | Part 4: From Localhost to Kubernetes Love how it rhymes "Production Kafka Producer". Here's to coding in an era of AI Agents. They suggest and are confident that this time it will work, but then this cluster has its own plan, and it starts misbehaving -- sometimes listens, and on others, feels cornered by his other siblings. This is the Tale of making the brothers
Ankit Agrahari
Feb 166 min read
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Building an AI Tutor with Spring AI, Ollama, and Vaadin
AI Tutor is a web application that uses Spring Boot and Spring AI on the backend, an Ollama -hosted LLM (e.g. Googleβs Gemma3) for natural language understanding, and Vaadin for the rich web UI. Its core innovation is a Retrieval-Augmented Generation (RAG) pipeline: when the user uploads course materials (PDFs, text, etc.), the app splits them into chunks, creates vector embeddings, and stores these in a PGVector -enabled PostgreSQL database. At chat time, similar chunk
Ankit Agrahari
Jan 115 min read
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Morphous AI: Building Multi-Modal AI Workflows with Spring Boot and Vaadin
Multi-modal AI workflows are becoming essential for modern backend systems. They allow applications to process and generate different types of dataβtext, images, audioβwithin a unified framework. This capability opens new possibilities for richer user experiences and more intelligent automation. The MorphousAI project, built with Spring Boot, Vaadin, and Spring AI, offers a practical example of how to implement such workflows in a backend-first Java environment. This article
Ankit Agrahari
Dec 17, 20255 min read
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Building the Foundation: APIs, Prompts, and First Runs
In Part 1 of this series, we introduced the Smart DevOps Assistant (SDA) β an AI-powered helper that reviews pull requests, generates...
Ankit Agrahari
Sep 27, 20254 min read
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Meet Smart Devops Assistant: Vision, Stack and Journey so far
PRs that review themselves. Tests that write themselves. Stand-ups that summarise themselves. Say hello to Smart DevOps Assistant (SDA)...
Ankit Agrahari
Aug 27, 20256 min read
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![If this shifted how you think about AI β
you're ready to Harness it. π₯
π¬ Comment "HARNESS" below
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![You think HashMap is always O(1).
It isn't. Here's what actually happens. π§΅
HashMap stores pairs using `index = hash(key) % capacity` β direct slot access, no scanning. Pure O(1). Until two keys land on the same slot. That's a collision β not a bug, a math inevitability.
Two ways to fix it π
π Chaining β each bucket holds a linked list. Collisions append to the list. Simple, handles high load, easy deletion. Downside: pointer overhead, poor cache performance, chains degrade to O(n) at high load. Java's fix? At 8 nodes, the list auto-converts to a Red-Black Tree β O(log n) worst case.
π¦ Open Addressing β no linked lists. Collision at slot X? Probe X+1, X+2 until empty. Cache-friendly, zero memory overhead. Downside: deletion needs tombstone markers, and keys cluster together making future collisions worse. Used by C++, Go, Redis.
βοΈ Load Factor = entries Γ· capacity
π’ Below 0.5 β rare collisions, wasted memory
π 0.75 β Java's sweet spot, triggers resize + rehash
π΄ Above 0.9 β collision cascade, O(n) territory
Double hashing kills clustering by varying the probe step per key:
`probe(i) = (h1 + i Γ h2) % m`
Elements scatter evenly. No bunching. O(1) preserved.
The truth: HashMap is O(1) until a bad hash function, wrong load factor, or wrong strategy turns it into O(n).
Three things protect you:
β Well-distributed hash function
β Load factor under 0.75
β Right collision strategy for your use case
π¬ Java interview question: what happens when a chain hits 8 nodes?
Drop your answer below π
π Save this before your next interview.
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