Author: Hooopo (Active contributor of Ruby China)

Editor: Ran Huang

An original version of this article was published on

This tutorial, perhaps, is the first Rails + TiDB integration tutorial across the web. TiDB is an open-source, distributed SQL database that features horizontal scalability, high availability, and MySQL compatibility.

For beginners, integrating a complex ORM like ActiveRecord with TiDB could be difficult. Since there are few articles on the web touching this topic, I wrote this tutorial to help Rails users to get started with TiDB.

Build a local TiDB development environment

Before integrating with Rails, you need to deploy a TiDB cluster on your local machine. TiDB provides a smooth deployment experience using TiUP, a package manager for the TiDB ecosystem.

Install TiUP

Installing TiUP is pretty straightforward for either Darwin or Linux operating systems. All you need to do is a single line of command:

{{< copyable “shell-regular” >}}

curl --proto '=https' --tlsv1.2 -sSf | sh

This will also add $HOME/.tiup/bin in your PATH environment variable, so you can use TiUP directly.

Spin up a local cluster

As a typical TiDB cluster requires multiple nodes, deploying it might be time-consuming and complicated. Therefore, TiUP offers playground, a TiUP component that enables you to quickly build a local TiDB test environment.

The command is as simple as follows:

{{< copyable “shell-regular” >}}

tiup playground

You’ll see the output like this:

tiup playground
Starting component ``playground``: /Users/hooopo/.tiup/components/playground/v1.4.1/tiup-playground
Use the latest stable version: v5.0.0

    Specify version manually: tiup playground <version>
    The stable version: tiup playground v4.0.0
    The nightly version: tiup playground nightly

Playground Bootstrapping...
Start pd instance
Start tikv instance
Start tidb instance
Waiting for tidb instances ready ... Done
Start tiflash instance
Waiting for tiflash instances ready ... Done
To connect TiDB: mysql --host --port 4000 -u root -p (no password)
To view the dashboard:
To view the Prometheus:
To view the Grafana:

Congrats! Your local cluster is now up and running.

Access TiDB Dashboard

TiDB provides TiDB Dashboard, a Web UI for monitoring your cluster. It is already built into the PD component, so you can directly access it via

TiDB Dashboard overview

For more information on TiUP, see the official documentation.

Configure Rails for TiDB

Now that you have a running TiDB cluster, the next step is to integrate it with Rails.

Create a Rails project

Because TiDB is compatible with MySQL, you can create a Rails app configured for MySQL:

rails new myapp --database=mysql

Configure database.yml

There are two configurations you need to pay attention to in database.yml:

  • Set port to 4000. The local TiDB cluster uses 4000 as the default port.
  • Set the database connection variable tidb_enable_noop_functions to ON. Rails needs to use the get_lock function. It is not implemented in TiDB, but a workaround is available.
default: &default
  adapter: mysql2
  encoding: utf8mb4
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  port: 4000
  username: root
    tidb_enable_noop_functions: ON

If you configure the database connection using the URI method, the configuration is similar:

default: &default
  adapter: mysql2
  encoding: utf8mb4
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  url: <%= ENV.fetch("DB_URL") || "mysql2://root:pass@localhost:4000/myapp" %>
    tidb_enable_noop_functions: ON

Configure primary key, auto-increment, unique-index

Create a table named users:

class CreateUsers < ActiveRecord::Migration[6.1]
  def change
    create_table :users do |t|
      t.string :email
      t.string :password
      t.string :username


Add a unique index:

class AddUniqueIndexForEmail < ActiveRecord::Migration[6.1]
  def change
    add_index :users, :email, unique: true

Because TiDB is compatible with MySQL, the usage is almost identical to that of a standalone MySQL database. Compared with other distributed databases that are incompatible in terms of features like primary keys, auto-increment, and unique indexes, TiDB is much more easy to get started with because no extra handling is required.

Now you can take a look at the generated data table:

mysql> show create table users;
+ -------+------------------------------------------------------------------------------------------------------------------------- ---------------------------------------------------------------------------------------------------------------------------------- ---------------------------------------------------------------------------------------------------------------------------------- -------------------------------------------------------------+
| Table | Create Table |
+-------+------------------------------------------------------------------------------------------------------------------------- ---------------------------------------------------------------------------------------------------------------------------------- ---------------------------------------------------------------------------------------------------------------------------------- -------------------------------------------------------------+
| users | CREATE TABLE `users` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `email` varchar(255) DEFAULT NULL,
  `password` varchar(255) DEFAULT NULL,
  `username` varchar(255) DEFAULT NULL,
  `created_at` datetime(6) NOT NULL,
  `updated_at` datetime(6) NOT NULL,
  PRIMARY KEY (`id`) /*T![clustered_index] CLUSTERED */,
  UNIQUE KEY `index_users_on_email` (`email`)
+-------+------------------------------------------------------------------------------------------------------------------------- ---------------------------------------------------------------------------------------------------------------------------------- ---------------------------------------------------------------------------------------------------------------------------------- -------------------------------------------------------------+
1 row in set (0.01 sec)

Add a patch for savepoints

The only obstacle to combining TiDB and ActiveRecord is that TiDB doesn’t support savepoints for now, so I wrote a simple patch to solve it:

require 'active_record/connection_adapters/abstract/database_statements.rb'

module DisableSavepoint
  def transaction(requires_new: nil, isolation: nil, joinable: true)
    if requires_new
      requires_new = nil
      Rails.logger.warn "savepoint statement was used, but your db not support, ignored savepoint."
      Rails.logger.warn caller
      super(requires_new: requires_new, isolation: isolation, joinable: joinable)
      super(requires_new: requires_new, isolation: isolation, joinable: joinable)

ActiveRecord::ConnectionAdapters::DatabaseStatements.send(:prepend, DisableSavepoint)

In Rails, savepoints are introduced only when the transaction passes true to the parameter requires_new. When that happens, this patch will change the value of requires_new to nil and output logs for migration.

From my experience, most Rails projects don’t use savepoints very often, so migration wouldn’t be much of a problem if needed. A savepoint is introduced when you perform migration, but if there’s no concurrent migration, removing it won’t bring unexpected consequences.



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