Zero-Downtime PostgreSQL Schema Migrations: Expand/Contract vs Blue-Green Deployment

Head-to-head comparison of expand/contract pattern and blue-green deployment for PostgreSQL schema migrations. Cover advisory locks, ghost tables, CREATE INDEX CONCURRENTLY, pg_advisory_lock. Practical SQL examples. CI/CD pipeline integration. Targeted SEO keywords: expand contract pattern vs blue green deployment postgresql schema migrations zero downtime, postgres zero downtime schema migration, postgres schema changes without downtime