when should you consider sharding your database?

hey everyone, ive been thinking a lot about scaling databases recently, specifically around when sharding becomes a necessary step rather than just an optimization. Weve hit a point where our current single instance, even with read replicas, is showing signs of strain under heavy write loads. Im curious to hear about your experiences. At what point did you decide sharding was the way to go? What were the key indicators or pain points that pushed you towards it? And what were the biggest challenges you faced during the implementation and ongoing maintenance?