TiDB, an open-source, distributed SQL database, has emerged as a solution to the challenges of building multitenant applications, particularly when it comes to managing data storage. In a previous article, we explored the various approaches to managing data for multitenant applications, including share-nothing, share-everything, and hybrid models. However, traditional databases and data management systems struggle to maintain performance while ensuring strict data isolation and security across tenants.

This challenge stems from the inherent conflict between shared resources and isolation requirements. As more tenants share the same infrastructure, the overhead of maintaining strict boundaries and preventing resource contention grows exponentially, leading to degraded performance and increased complexity in access control mechanisms. Distributed SQL databases, like TiDB, have emerged as a response to these challenges, combining the simplicity and reliability of traditional SQL databases with the scalability and performance typically associated with NoSQL systems.

TiDB's architecture is designed for high availability and scalability, elastically scaling out to hundreds of nodes and managing petabytes of data while supporting millions of queries per second (QPS). The architecture consists of three main components: a distributed storage layer (TiKV), a SQL layer (TiDB Server), and a scheduling layer (Placement Driver or PD). TiKV is a transactional key-value storage engine that shards data into small chunks, each represented as a split, and replicates data across multiple nodes in the cluster using the Raft consensus algorithm to ensure data redundancy and fault tolerance.

TiDB Server, the SQL layer, communicates with applications, processes all SQL commands and queries, and works with the storage layer to process data. TiDB Server nodes are stateless, allowing them to scale horizontally with ease. This enables the database to easily expand capacity and throughput as demand increases. The SQL layer implements the MySQL protocol, providing users a familiar SQL interface while extending additional capabilities for handling distributed transactions.

The Placement Driver (PD) plays a critical role in maintaining the health of the database system by managing the metadata of the storage engine. It acts like a devops staffer who monitors the TiDB cluster around the clock, load balancing, placing data, facilitating operations, and ensuring data safety. PD collects information on each TiKV node to build a global view of the whole cluster, identifying any violations of admin policies, load imbalances, and proactive actions needed during operations like rolling upgrades.

TiDB's architecture provides the basis for a range of features critically important to multitenant applications, including horizontal scalability, high availability, flexible deployment, online schema migration, and resource control groups. Horizontal scalability allows each component to scale independently without downtime or performance degradation, while high availability minimizes the blast radius of potential failures. Flexible deployment enables organizations to deploy TiDB on general-purpose machines, whether on-premises or in the cloud, and integrate with Kubernetes for automated deployment, scaling, and life cycle management.

Online schema migration allows developers to roll out new features without service interruption, while resource control groups enable administrators to monitor and manage the resource consumption of each tenant, preventing any one from consuming disproportionate resources that could affect the overall system performance. These features make TiDB an attractive solution for businesses looking to leverage multitenancy for efficiency and growth.

Distributed SQL databases like TiDB represent a major step forward for multitenant applications, offering more robust support for multitenant data management than legacy SQL and NoSQL systems. With their roots in hyperscale web applications, they are better positioned to address the key needs of multitenant architectures – scalability, consistency, availability, and flexibility – while also providing advanced features for resource management and data placement.

As the technology landscape continues to evolve, solutions like TiDB are poised to play a critical role in enabling businesses to efficiently manage multitenant applications and unlock new opportunities for growth and innovation.