Hugely useful but also hugely different from an engineering/coverage perspective, perhaps.
Companies with more data than can fit in a single-instance RDBMS system (like >3TB of hot data, more throughput than a single node can handle) but still seeking transactional consistency are a clear use case. Single-person startups could definitely benefit, but it's a less-likely scenario that they would require the level of coverage Spanner provides.
Companies with more data than can fit in a single-instance RDBMS system (like >3TB of hot data, more throughput than a single node can handle) but still seeking transactional consistency are a clear use case. Single-person startups could definitely benefit, but it's a less-likely scenario that they would require the level of coverage Spanner provides.