Vanakkam

Write-ups of real customer problems from the field, with the diagrams I wish the docs had.

Occasionally travel, cooking, cricket, DIY and whatever is going on in the garden.

Series

• RAG Retrieval Non-Determinism

  Why an identical query returns a different top 10, and how to bound the variance instead of chasing determinism.

  1. Part 1: Why Your RAG Search Returns Different Results Every Time
  2. Part 2: Fixing Unstable RAG Retrieval

• Zero-Downtime Multi-TB Migrations

  Moving 12 TB from PostgreSQL 11 on-prem to a managed PostgreSQL 16 with five-minute write pauses: planning the waves, then running them.

  1. Part 1: Zero-Downtime Multi-TB Migrations: Strategy and Grouping
  2. Part 2: Zero-Downtime Multi-TB Migrations: Cutover, Validation and Rollback

Featured

• RDS MySQL Blue/Green Upgrades: Don't Let Debezium Lose Its Place

  Updated: 15 Sep, 2026

  How to run a major version upgrade on RDS MySQL without breaking your Debezium CDC pipeline. Covers binlog position recovery, GTID auto-positioning, and how to verify you did not lose any changes.

• Cut Your LLM Bill by 80% Without Shipping a Worse Product

  15 Sep, 2026

  Cost-tiered model routing: send the routine 80% of traffic to a small model, verify the answer before you trust it, and keep the expensive model for the work that actually needs it. Provider-neutral architecture, the arithmetic, and the parts that go wrong.

• Streaming Aurora DSQL Changes into an Iceberg Lakehouse with Firehose

  15 Jul, 2026

  Aurora DSQL CDC is GA. Here's how to build a fully managed pipeline that lands committed changes in Apache Iceberg on S3 Tables via Kinesis and Firehose, and the record-format details you need to get right.

• Altering a big table online: ADD column with near-zero downtime on MySQL 8+ and Postgres 14+

  Updated: 21 May, 2026

  A practical, cloud-agnostic look at adding columns to large tables without downtime — what MySQL 8+ and Postgres 14+ actually let you do, the expand-contract pattern that beats native DDL alone, the OSS tools, and the managed-service caveats.

• Aurora to Redshift Zero-ETL: what actually replicates

  16 Feb, 2026

  A practical look at Aurora PostgreSQL Zero-ETL into Redshift — how NOT NULL really behaves, why your PostgreSQL indexes don't translate, and how retries stay idempotent without enforced uniqueness.

• Why Is My PostgreSQL Major Version Upgrade So Slow?

  27 Sep, 2025

  A deep dive into why PostgreSQL major version upgrades take longer than expected — what actually happens under the hood, why parallelism won't save you, and how to diagnose the bottleneck. Applies to Aurora PostgreSQL, RDS PostgreSQL, and self-hosted.

• Troubleshooting Data Dictionary Issues in MySQL and Aurora

  26 Mar, 2025

  A practical guide to understanding, diagnosing, and resolving MySQL Data Dictionary inconsistencies on RDS MySQL and Aurora MySQL — before they become emergencies.

• Hello, I'm Venki — and welcome to my notes

  1 Jan, 1988

  A short introduction to who I am and what this blog is going to be about — a mix of tech, travel, cooking, cricket, DIY, and gardening.