Why doesn't Spanner support auto-incrementing primary keys?

Spanner deliberately omits a native auto-increment or identity-column feature because it conflicts with how the database achieves horizontal scale. An auto-incrementing sequence, by definition, produces monotonically increasing values, and since rows are stored in primary-key order, every new row would land in the same split, creating exactly the write hotspot Spanner's distributed architecture is designed to avoid.

A single-node database can afford auto-increment because there's only one place for writes to go anyway, but that assumption breaks down once data is sharded across many machines. Instead, Spanner encourages key strategies that preserve uniqueness without sequential order: UUIDs, bit-reversed sequence values, or a hash prefix combined with a secondary ordering column when insertion order still needs to be queryable through an index rather than the primary key itself.

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