When should you think about database sharding

hey folks, i've been thinking a lot about scaling databases lately. we've hit a point where our single PostgreSQL instance is starting to struggle with read/write loads, and i'm wondering about the tipping point for sharding. what are the key indicators that tell you it's time to explore sharding versus other scaling strategies like read replicas or vertical scaling? are there specific query patterns or data sizes that scream 'shard me'? curious to hear your experiences and what pitfalls to watch out for