Youll spend your first 90 days learning it deeply, embedded with the teams that built it, and take ownership of its architecture domain by domain: starting with the data and transaction layer, then service architecture and the cloud platform. Deep database expertise: relational (PostgreSQL, MySQL, or Oracle) including query tuning, indexing, sharding, and replication, plus NoSQL and caching (e.g., Cassandra, MongoDB, DynamoDB, Redis).