Liquibase on multiple databases

As you can see in the documentation, you can use two different executions, like this:

<plugin>
  <groupId>org.liquibase</groupId>
  <artifactId>liquibase-maven-plugin</artifactId>
  <version>3.0.5</version>
  <executions>
    <execution>
      <phase>process-resources</phase>
      <configuration>
        <changeLogFile>PATH_TO_CHANGELOG_1</changeLogFile>
        ... connection properties  ...
      </configuration>
      <goals>
        <goal>update</goal>
      </goals>
    </execution>
   <execution>
      <phase>process-resources</phase>
      <configuration>
        <changeLogFile>PATH_TO_CHANGELOG_2</changeLogFile>
        ... connection properties  ...
      </configuration>
      <goals>
        <goal>update</goal>
      </goals>
    </execution>
  </executions>
</plugin>

The only problem with this approach is that you need two different changelog.xml files, one per database.

Also, you can have preconditions in your changelog file to choose between what changeset will be processed by each database.

For example:

<changeSet id="1" author="bob">
    <preConditions onFail="MARK_RAN">
         <dbms type="oracle" />
    </preConditions>
    <comment>Comments should go after preCondition. If they are before then liquibase usually gives error.</comment>
    <dropTable tableName="oldtable"/>
</changeSet>

The onFail="MARK_RAN" makes Liquibase skip the changeset but marks it as run, so the next time it will not try again. See the customPrecondition tag in the documentation for more complex preconditions.

You may want to have 2 separate changelogs to manage the two databases, even if they are both used by the same application.

As Arturo says you can have 2 or more execution-nodes, but you must give every execution-node a seperate id.

                <plugin>
                    <groupId>org.liquibase</groupId>
                    <artifactId>liquibase-maven-plugin</artifactId>
                    <version>3.0.5</version>
                    <executions>
                        <execution>
                            <id>db1-update</id>
                            <phase>process-resources</phase>
                            <configuration>
                                <changeLogFile>src/main/resources/org/liquibase/db1.xml</changeLogFile>
                                <driver>org.postgresql.Driver</driver>
                                <url>jdbc:postgresql://localhost/db1</url>
                                <username>..</username>
                                <password>..</password>
                            </configuration>
                            <goals>
                                <goal>update</goal>
                            </goals>
                        </execution>
                        <execution>
                            <id>db2-update</id>
                            <phase>process-resources</phase>
                            <configuration>
                                <changeLogFile>src/main/resources/org/liquibase/db2.xml</changeLogFile>
                                <driver>org.postgresql.Driver</driver>
                                <url>jdbc:postgresql://localhost/db2</url>
                                <username>...</username>
                                <password>...</password>
                            </configuration>
                            <goals>
                                <goal>update</goal>
                            </goals>
                        </execution>
                        <execution>
                            <id>db3-update</id>
                            <phase>process-resources</phase>
                            <configuration>
                                <changeLogFile>src/main/resources/org/liquibase/db3.xml</changeLogFile>
                                <driver>org.postgresql.Driver</driver>
                                <url>jdbc:postgresql://localhost/db3</url>
                                <username>...</username>
                                <password>...</password>
                            </configuration>
                            <goals>
                                <goal>update</goal>
                            </goals>
                        </execution>
                    </executions>
                </plugin>

You can use Preconditions inside changeset or changelog and give conditions according to the database,

<preConditions  onFail="WARN">
    <dbms  type="oracle"  />
    <runningAs  username="SYSTEM"/>
</preConditions>

Like this, you can use precondition tag inside changeset and give conditions according to each database.

Use this link for additions documentation.

Old question but I still answer cause I have the same requirement today, and I am opting for another solution.

I would recommend, if you can, as proposed already in the answers to use seperate changelogs.

But if you want to keep the changelogs unified, as I need for my specific case, I would use labels instead of preconditions to filter changesets to be executed.

<changeSet id="0001:1" author="oz" labels="clickhouse">
    <sql>...SOMESQL...</sql>
</changeSet>

<changeSet id="0001:2" author="oz" labels="mongodb">
    <ext:createCollection collectionName="myCollection">
         ...SOMEJSON....
    </ext:createCollection>
</changeSet>

This will prevent poluting the databasechangelog of the two databases with the executions of the changesets of the other database. This will cause problems(for the current release at least 4.6.1) for any liquibase operation using tags, such as rollbackToTag or updateToTag.