Dhiraj Kumar's Blog

Category: oracle

  • Pointing RAG at a Real Document: What Breaks and Why

    Fourth post in this series. The earlier ones used six tidy passages I wrote myself, which is a fine way to learn the mechanics and a terrible way to find out whether any of it works. This time I loaded a 323 KB file of my own working notes — a support chat transcript full…

  • Semantic Search Without Leaving the Database: Loading an ONNX Model into Oracle AI Database 26ai

    In an earlier post I worked through vector distance using numbers I typed by hand. That covers the mechanics, but it leaves the interesting half untouched: where do real vectors come from, and does semantic search actually work on text? This post answers both. The model runs inside the database. No network calls, no cloud…

  • Finding the Nearest Vector in Oracle AI Database 26ai: Three Methods

    Normal SQL search matches characters. WHERE content LIKE ‘%RAC%’ finds rows containing those three letters and nothing else. If a customer describes “cluster node eviction” and my notes say “instance was evicted from the cluster”, a LIKE search finds nothing — different words, same meaning. Vector search solves that. Text is converted into a list…

  • Mastering Oracle AI Vector Search: Vector Constructors and Distance Metrics Made Simple

    With Oracle Database 26ai, SQL gains native support for AI workloads through Oracle AI Vector Search. At the heart of similarity search lies two foundational concepts: constructing vectors directly in SQL and calculating the mathematical distance between them. 1. Creating Vectors on the Fly: The VECTOR Constructor Real-world embedding models (like OpenAI’s text-embedding-3-small or Cohere’s…

  • Troubleshooting High gc freelist Waits in Oracle RAC: Root Cause and Resolution

    In an Oracle Real Application Clusters (RAC) environment, batch jobs or maintenance tasks that typically run in minutes can occasionally encounter severe bottlenecks. A common yet elusive culprit is the gc freelist wait event. The Scenario A routine batch job—responsible for disabling and enabling constraints across schemas normally finishes within 1 to 2 minutes. Suddenly,…

  • Oracle RAC Grid Infrastructure Upgrade Failure: When “Downgrade Successful” Isn’t Actually Successful (19c → 26ai)

    When a major-version Grid Infrastructure upgrade fails partway through, Oracle gives you a documented recovery path: the “Online Terminate Upgrade” downgrade procedure. It’s well documented, it runs clean, and it tells you it succeeded. But in a real 2-node RAC test cluster, following that exact procedure left the cluster in a state where CRS simply…

  • Oracle RAC Grid Infrastructure Upgrade from 19c to 26ai (23c) with Real Logs

    Upgrading Oracle Grid Infrastructure (GI) from 19c to 26ai (23c internally) is a critical task for RAC environments. While Oracle provides documentation, real-world execution often requires additional clarity. In this guide, I will walk through a complete step-by-step upgrade of a 2-node RAC cluster, using actual commands and logs from a real upgrade scenario. Nodes:…