What is a changeLog in Liquibase?

A changeLog is the master configuration file (or set of files) that contains all the database changes Liquibase should manage. It acts as the single source of truth for every schema modification your application has ever needed — from the initial table creation to the latest column rename. Liquibase reads this file on every run and decides which changeSets to apply based on what's already recorded in the database tracking table.

A changeLog can be written in four formats: XML, YAML, JSON, or formatted SQL. XML is the most common in enterprise Java projects. Here's a minimal example:

<?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-4.9.xsd">

    <changeSet id="1" author="alice">
        <createTable tableName="customer">
            <column name="id" type="BIGINT" autoIncrement="true">
                <constraints primaryKey="true" nullable="false"/>
            </column>
            <column name="email" type="VARCHAR(255)"/>
        </createTable>
    </changeSet>
</databaseChangeLog>

For large projects it is common to split the changeLog into multiple files organised by version or feature, and then include them from a root changeLog using the <include> or <includeAll> tags. This keeps individual files manageable and makes code reviews easier — each pull request only adds a new changeSet file rather than modifying a single growing file.