PostgreSQL Field Notes

Notes for the problems that show up after launch: bad plans, awkward migrations, index debt, vacuum pressure, replica lag, and the small decisions that make PostgreSQL easier to operate.

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SQL Server MariaDB MySQL pgvector and RAG Indexes Slow Queries Locks and Transactions Backups and Durability Replication and WAL Connections and Pooling CPU, Memory, and I/O Vacuum and Bloat Cloud Providers

May 8, 202610 min read

PostgreSQL Lock Queues: Why One Migration Can Freeze the App

One ALTER TABLE froze the whole app for ninety seconds, and it wasn't even slow. It was stuck behind a long query, holding a lock everyone else then queued behind. Here's how I stopped doing that.

May 8, 202610 min read

PostgreSQL JSONB Performance: GIN Indexes, TOAST, and Query Shape

JSONB shipped us fast and then quietly got slow. The lessons that stuck: index for your real query shape, watch TOAST on wide documents, and stop selecting the whole blob.

May 4, 20266 min read

RAG Quality Metrics: Stop Measuring Only Latency

A fast RAG system can still be wrong. Production teams need recall@k, MRR, answerability, citation coverage, freshness, no-hit rate, and drift signals.

May 4, 20265 min read

Vector Database Cost Model: Why Your RAG Bill Explodes

Vector cost is not just storage. Dimensions, top_k, filters, rerankers, embedding refreshes, payload size, index rebuilds, and tenant skew all compound.

May 4, 20266 min read

Chunking Is a Database Design Problem, Not a Prompting Trick

Chunk size and overlap decide retrieval quality, citation accuracy, freshness, permissions, and cost. Treat chunks as serving data with ownership.

May 4, 20266 min read

Multi-Tenant Vector Search: Namespaces, Metadata Filters, or Partitions?

Multi-tenant vector search is a correctness and isolation problem. Namespaces, filters, and partitions each fail differently under tenant skew and ACL rules.

May 4, 202611 min read

PostGIS in Production: Why Geo Queries Get Slow After the Demo

Slow PostGIS systems usually do not fail because geography is hard. They fail because the query shape stops the spatial index from pruning work early.

May 4, 20266 min read

Hybrid Search in Production: BM25 Plus Vector Is Not a Magic Button

Hybrid search helps when exact terms and semantic meaning both matter. It fails when teams blend rankings without query intent, calibration, or evaluation.

May 4, 202612 min read

TimescaleDB in Production: When Time-Series Postgres Starts Hurting

TimescaleDB helps when the pain is truly time-series pain. Chunk interval, compression windows, retention, late data, and aggregate refresh policies decide whether it stays boring.

May 4, 20266 min read

Re-Embedding Without Breaking Production Search

Embedding model upgrades are migrations. Versioned embeddings, dual indexes, shadow queries, backfills, and rollback decide whether search quality survives.

May 4, 202610 min read

PostgreSQL 18 New Features: What Actually Matters in Production

PostgreSQL 18 is already here. The useful question is not whether the release is exciting, but which features reduce real production pain and which upgrade risks need rehearsal.

May 4, 20265 min read

Vector Deletes, Freshness, and Permissions: The Hidden RAG Incident

A RAG system is unsafe if deleted documents, permission changes, and stale embeddings can still appear in answers. Freshness is part of correctness.