Decomposing the GitLab backend database, Part 3: Challenges and surprises

What this post added

This post details challenges encountered during the database decomposition migration, including issues with autovacuum locking, unexpected database connections from long-running SSH sessions, missed cron jobs, and Sentry server overload. It also discusses the impact of cascading replication on CI read-only traffic latency and the complexities of incrementally re-balancing PGBouncer connections without saturating the main Postgres database.