Multiple database connections

Oct 13, 2025 by windailys.com 42 views

Introduction

When working with Spring Boot and Liquibase, it's not uncommon to encounter issues after importing a production database dump into your development environment. One such issue is the "Expected single row from SelectFromDatabaseChangeLogLockStatement but got 2" error, which can prevent your Spring Boot services from starting. In this article, we'll explore the causes of this error and provide a step-by-step guide on how to resolve it.

Understanding the Error

The "Expected single row from SelectFromDatabaseChangeLogLockStatement but got 2" error occurs when Liquibase attempts to acquire a lock on the database change log table. This lock is used to prevent concurrent modifications to the database schema. However, when you import a production database dump into your development environment, the lock table may already contain multiple rows, causing Liquibase to fail.

Causes of the Error

There are several reasons why you may encounter this error after importing a production database dump:

Multiple database connections: If you have multiple Spring Boot services sharing the same database, each service may attempt to acquire a lock on the database change log table, leading to conflicts.
Existing database schema: If the production database dump contains an existing database schema, Liquibase may attempt to apply changes to the schema, causing the lock exception.
Liquibase configuration: Incorrect or incomplete Liquibase configuration can lead to lock exceptions.

Resolving the Error

To resolve the "Expected single row from SelectFromDatabaseChangeLogLockStatement but got 2" error, follow these steps:

Step 1: Check Liquibase Configuration

Review your Liquibase configuration to ensure that it is correct and complete. Check the following:

Liquibase version: Ensure that you are using the latest version of Liquibase.
Database connection: Verify that the database connection is correct and that the database is accessible.
Change log table: Check that the change log table is correctly configured and that the lock table is not already populated.

Step 2: Drop the Lock Table

If the lock table is already populated, you can drop it to resolve the issue. However, be cautious when dropping tables, as this can lead to data loss.

DROP TABLE databasechangeloglock;

Step 3: Update Liquibase Configuration

Update your Liquibase configuration to include the following properties:

liquibase.lock-table: Set this property to false to disable the lock table.
liquibase.drop-first: Set this property to true to drop the change log table before applying changes.

<liquibase
    xmlns="http://www.liquibase.org/xml/ns/dbchangelog"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog
    http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-3.1.xsd"
    defaultSchemaName="public"
    changeLog="classpath:db/changelog/db.changelog-master.xml"
    context-sources="classpath:db/changelog/context.xml"
    liquibase.lock-table="false"
    liquibase.drop-first="true">
</liquibase>

Step 4: Re-Run Liquibase

Re-run Liquibase to apply the changes to the database schema.

mvn liquibase:update

Step 5: Verify the Issue

Verify that the issue is resolved by checking the Spring Boot services for any errors or exceptions.

Conclusion

The "Expected single row from SelectFromDatabaseChangeLogLockStatement but got 2" error can be a frustrating issue to resolve, especially when working with Spring Boot and Liquibase. By following the steps outlined in this article, you should be able to resolve the issue and get your Spring Boot services up and running again.

Additional Tips and Considerations

Use a separate database for development: Consider using a separate database for development to avoid conflicts with the production database.
Use a version control system: Use a version control system to track changes to the database schema and ensure that all team members are working with the same version.
Test thoroughly: Thoroughly test your Spring Boot services after resolving the issue to ensure that they are working as expected.

Resources

Liquibase Documentation
Spring Boot Documentation
PostgreSQL Documentation
Spring Boot + Liquibase: Q&A =============================

Introduction

In our previous article, we explored the causes and resolution of the "Expected single row from SelectFromDatabaseChangeLogLockStatement but got 2" error when working with Spring Boot and Liquibase. In this article, we'll answer some frequently asked questions (FAQs) related to Spring Boot, Liquibase, and database schema management.

Q&A

Q: What is Liquibase and why do I need it?

A: Liquibase is an open-source database migration tool that helps you manage changes to your database schema. It's a must-have when working with Spring Boot, as it ensures that your database schema is up-to-date and consistent across all environments.

Q: How do I configure Liquibase in my Spring Boot application?

A: To configure Liquibase in your Spring Boot application, you'll need to add the following dependencies to your pom.xml file:

<dependency>
    <groupId>org.liquibase</groupId>
    <artifactId>liquibase-core</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-liquibase</artifactId>
</dependency>

You'll also need to create a liquibase.properties file in the root of your project, which will contain your Liquibase configuration settings.

Q: How do I create a change log in Liquibase?

A: To create a change log in Liquibase, you'll need to create a new XML file in the db/changelog directory of your project. This file will contain the changes you want to apply to your database schema.

Here's an example of a simple change log:

<?xml version="1.0" encoding="UTF-8"?>
<databaseChangeLog
    xmlns="http://www.liquibase.org/xml/ns/dbchangelog"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog
    http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-3.1.xsd">
&lt;changeSet id=&quot;1&quot; author=&quot;your_name&quot;&gt;
    &lt;createTable tableName=&quot;users&quot;&gt;
        &lt;column name=&quot;id&quot; type=&quot;int&quot; autoIncrement=&quot;true&quot;&gt;
            &lt;constraints primaryKey=&quot;true&quot; nullable=&quot;false&quot;/&gt;
        &lt;/column&gt;
        &lt;column name=&quot;name&quot; type=&quot;varchar(255)&quot;&gt;
            &lt;constraints nullable=&quot;false&quot;/&gt;
        &lt;/column&gt;
        &lt;column name=&quot;email&quot; type=&quot;varchar(255)&quot;&gt;
            &lt;constraints nullable=&quot;false&quot;/&gt;
        &lt;/column&gt;
    &lt;/createTable&gt;
&lt;/changeSet&gt;

</databaseChangeLog>

Q: How do I run Liquibase in my Spring Boot application?

A: To run Liquibase in your Spring Boot application, you'll need to add the following configuration to your application.properties file:

spring.liquibase.enabled=true
spring.liquibase.url=jdbc:postgresql://localhost:5432/mydatabase
spring.liquibase.username=myusername
spring.liquibase.password=mypassword

You can then run the following command to apply the changes to your database schema:

mvn liquibase:update

Q: What are some best practices for database schema management with Liquibase?

A: Here are some best practices for database schema management with Liquibase:

Use a separate database for development: Consider using a separate database for development to avoid conflicts with the production database.
Use a version control system: Use a version control system to track changes to the database schema and ensure that all team members are working with the same version.
Test thoroughly: Thoroughly test your Spring Boot services after applying changes to the database schema to ensure that they are working as expected.
Use a consistent naming convention: Use a consistent naming convention for your database tables and columns to make it easier to manage your database schema.
Document your database schema: Document your database schema to make it easier for others to understand and work with your database.

Conclusion

In this article, we've answered some frequently asked questions related to Spring Boot, Liquibase, and database schema management. By following the best practices outlined in this article, you can ensure that your database schema is up-to-date and consistent across all environments.