Database sharding is a common strategy for scaling relational databases, but it introduces a set of complex problems that can undermine system reliability. This article systematically identifies seven major categories of issues: distributed transaction consistency, unique ID generation with clock drift protection, cross-shard queries and pagination, data migration, global sequence generation, multi-shard aggregation, and schema changes. For each problem, the author presents proven solutions such as TCC (Try-Confirm/Cancel) transactions, snowflake ID algorithms with clock skew handling, cursor-based pagination, and dual-write migration strategies. The content is grounded in real-world experience and includes code snippets for key components like a custom sharding algorithm and a distributed ID generator. This is essential reading for any backend engineer or architect designing a horizontally scalable database layer.
A comprehensive guide to the seven key challenges of database sharding, with practical solutions and code examples for distributed transactions, ID generation, and pagination.