Database Sharding: When is it too much trouble?

were hitting some serious scale issues with our primary user database. Sharding seems like the next logical step to distribute the load and improve query performance. But, Im concerned about the operational overhead, managing shards, handling cross-shard queries, and potential re-sharding down the line. Are there specific thresholds or patterns where sharding becomes a must-have, or are there scenarios where sticking with a well-optimized single instance or read replicas is a better long-term play? Lets discuss the trade-offs.