Overview Here’s a problem-first mapping — each scenario describes a pressure point a web application hits, paired with the tools/patterns that address it. Scenarios Scenario: Your database is getting hammered by repeated identical reads (product pages, user profiles, config data) Solution: Redis or Memcached as a read-through cache, sitting in front of Postgres. The pattern … Read more
overview Recently, I upgraded from spring 3.5 to 4. It went quite smoothly thanks to openrewrite script. There are some hiccups of course (with jackson objectmapper, custom deserializer) but thanks to Claude, those are solved quite quickly. One strange thing is that liquibase checksum changed. Many past migrations failed due to this error (I don’t … Read more
Java gives you more than one way to coordinate access to shared state. Most developers start with synchronized and never look further — but understanding the full lock landscape, especially ReentrantLock, unlocks (pun intended) a set of capabilities that can be critical for production-grade concurrent code. This post covers the full picture: from the JVM … Read more
The most powerful feature of LangGraph is that it allows Cycles. You can draw an edge from Node B back to Node A. This creates a loop. The Scenario A “Coin Flip” game. The agent keeps flipping a coin until it gets “Heads”. The Code Output (Randomized) Key Concept: Recursion Limit If you ran this … Read more
A standard edge (add_edge) is like a train track; the train must go there. A conditional edge (add_conditional_edges) is like a junction. The graph pauses, looks at the State, and decides which track to take. To implement this, we need a special Routing Function. This function doesn’t update the state; it simply returns the name … Read more
To fix the overwrite issue in lesson 1, we need to tell LangGraph: “When you receive new data for ‘topics’, do not replace the old data. Add it to the old data.” We do this using a Reducer. In Python, the operator.add function adds two lists together ([‘a’] + [‘b’] = [‘a’, ‘b’]). We can … Read more