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Documentation
  • Introduction
  • Concepts
    • Architecture
    • Key Features
      • Horizontal Scalability
      • MySQL Compatible Syntax
      • Replicate from and to MySQL
      • Distributed Transactions with Strong Consistency
      • Cloud Native Architecture
      • Minimize ETL with HTAP
      • Fault Tolerance & Recovery with Raft
      • Automatic Rebalancing
      • Deployment and Orchestration with Ansible, Kubernetes, Docker
      • JSON Support
      • Spark Integration
      • Read Historical Data without Restoring from Backup
      • Fast Import and Restore of Data
      • Hybrid of Column and Row Storage
      • SQL Plan Management
      • Open Source
      • Online Schema Changes
  • How-to
    • Get Started
      • Start a Local Cluster
        • From Binary
        • From Homebrew
        • From DBdeployer
        • In Kubernetes
        • In Docker Compose
      • Explore SQL with TiDB
      • Import Sample Database
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    • Deploy
      • Hardware Recommendations
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        • For testing environments
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      • Orchestrated Deployment
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      • Constraints
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        • Function and Operator Reference
        • Type Conversion in Expression Evaluation
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        • Numeric Functions and Operators
        • Date and Time Functions
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        • Cast Functions and Operators
        • Encryption and Compression Functions
        • Information Functions
        • JSON Functions
        • Aggregate (GROUP BY) Functions
        • Miscellaneous Functions
        • Precision Math
      • SQL Language Structure
        • Literal Values
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        • Keywords and Reserved Words
        • User-Defined Variables
        • Expression Syntax
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      • Generated Columns
      • Transactions
        • Transaction Model
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      • Performance
        • Overview
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        • Introduction to Statistics
        • Optimizer Hints
        • Tune TiKV
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    • Configuration
      • tidb-server
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  • Releases
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TiDB Architecture

The TiDB platform is comprised of three key components: the TiDB server, the PD server, and the TiKV server. In addition, TiDB also provides the TiSpark component for complex OLAP requirements.

image alt text

TiDB server

The TiDB server is in charge of the following operations:

  1. Receiving the SQL requests

  2. Processing the SQL related logics

  3. Locating the TiKV address for storing and computing data through Placement Driver (PD)

  4. Exchanging data with TiKV

  5. Returning the result

The TiDB server is stateless. It does not store data and it is for computing only. TiDB is horizontally scalable and provides the unified interface to the outside through the load balancing components such as Linux Virtual Server (LVS), HAProxy, or F5.

Placement Driver server

The Placement Driver (PD) server is the managing component of the entire cluster and is in charge of the following three operations:

  1. Storing the metadata of the cluster such as the region location of a specific key.

  2. Scheduling and load balancing regions in the TiKV cluster, including but not limited to data migration and Raft group leader transfer.

  3. Allocating the transaction ID that is globally unique and monotonic increasing.

The PD server ensures redundancy by using the Raft consensus algorithm. The Raft leader is responsible for handling all operations, with remaining PD servers available for high availability only. It is recommended to deploy PD as an odd number of nodes.

TiKV server

The TiKV server is responsible for storing data. From an external view, TiKV is a distributed transactional Key-Value storage engine. Region is the basic unit to store data. Each Region stores the data for a particular Key Range which is a left-closed and right-open interval from StartKey to EndKey. There are multiple Regions in each TiKV node. TiKV uses the Raft protocol for replication to ensure the data consistency and disaster recovery. The replicas of the same Region on different nodes compose a Raft Group. The load balancing of the data among different TiKV nodes are scheduled by PD. Region is also the basic unit for scheduling the load balance.

TiSpark

TiSpark deals with the complex OLAP requirements. TiSpark makes Spark SQL directly run on the storage layer of the TiDB cluster, combines the advantages of the distributed TiKV cluster, and integrates into the big data ecosystem. With TiSpark, TiDB can support both OLTP and OLAP scenarios in one cluster, so the users never need to worry about data synchronization.

"TiDB Architecture" was last updated Feb 14 2019: architecture: clarify PDs usage (#852) (f4e9c99)
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