Database Schema Migrations in a High-Traffic, Zero-Downtime Environment?

Hey everyone, I'm curious about how teams are handling database schema migrations, especially in environments where downtime is absolutely not an option and traffic is consistently high. We're looking at evolving our main PostgreSQL database schema, and I'm trying to gather best practices beyond just `ALTER TABLE` operations. Are people using techniques like blue/green deployments for their databases, or perhaps some form of logical replication and swap? What are the common pitfalls you've encountered, and what tools or strategies have you found most effective for ensuring a smooth, zero-downtime transition during schema changes? Any real-world war stories or success stories would be awesome!