Database Isolation: Why Two Committed Transfers Can Create Money

·3 views

Two wallet transfers can both commit successfully while creating money. In Lab 08, the problem is a specific query pattern: read a balance, validate it in Go, calculate a replacement value, and write that value later. A transaction boundary does not make the original read remain current. The useful question is whether overlapping transactions preserve the business invariant. This lab approaches that question through a three-account wallet, PostgreSQL isolation experiments, and concurrent tests.

Read the full story at DEV Community

This is an AI-generated summary. ShortSingh links to the original source for the complete article.

Discussion (0)

Union-Find: The Matrix of Disjoint Sets

The Quest Begins (The "Why") I still remember the first time I stared at a LeetCode problem that asked me to count how many separate groups of friends existed in a social network. My initial instinct was to throw a nested loop at it, compare every pair, and mark visited nodes. The code worked on the tiny examples, but as soon as the input size crept past a few thousand, my solution started to feel like I was trying to bail out a sinking ship with a teaspoon. I was frustrated, not because I lacked effort, but because I was solving the wrong problem—I was treating connectivity as a series of pai

0 comments Read more at DEV Community

ProgrammingDEV Community ·

A practical growth loop for early products

Early growth gets clearer when treated as a learning loop, not a channel checklist. Start with one painful use case and a narrow audience. Then run small experiments that produce real conversations: a useful guide, a focused landing page, a lightweight tool, or a hands-on onboarding session. Track the signals that show learning: repeated customer language, activation, retention, and the objections that keep coming up. The best experiment is the one that improves the next message or product decision.

0 comments Read more at DEV Community

ProgrammingDEV Community ·

What goes in an approval request: a short reason or a link to the trace?

A reader left a comment on the approval queue post: should the request carry a short justification inline, or just link to the trace? Short answer: both, but they do different jobs, and they should never be mixed together in one block of text. Here is how we lay it out. ◆ Link only. The reviewer has to open a trace, scroll through tool calls and work out what happened before they can decide.

0 comments Read more at DEV Community

ProgrammingDEV Community ·

Why Vector RAG Answers Only Half of a Legal Question: Building a GraphRAG Agent That Follows the Law's Cross-References, in 5 Steps

TL;DR Statutes don't repeat themselves, they point: the penalty for violating Section 26 sits sixty sections away and shares no vocabulary with it, so vector search finds half the answer. This post builds the other half in five steps: section-level chunks, a 190-node knowledge graph of the law, dense + sparse embeddings in Qdrant, a 2-hop graph walk, and an MCP server a plain-Python agent can call. Code: github.com/aekanun2020/pdpa-graphrag-mcp From the 96 sections of Thailand’s PDPA to a 190-node knowledge graph, hybrid search, and an MCP server any agent can call — all running locally in Doc

0 comments Read more at DEV Community