liquibase-core/src/main/java/liquibase/Liquibase.java
public void tag(String tagString) throws LiquibaseException {
        LockService lockService = LockServiceFactory.getInstance().getLockService(database);
        lockService.waitForLock();

        try {
            ChangeLogHistoryServiceFactory.getInstance().getChangeLogService(database).generateDeploymentId();

            checkLiquibaseTables(false, null, new Contexts(),
                new LabelExpression());
            getDatabase().tag(tagString);
        } finally {
            try {
                lockService.releaseLock();
            } catch (LockException e) {
                LOG.severe(LogType.LOG, MSG_COULD_NOT_RELEASE_LOCK, e);
            }
        }
    }
public void tag(String tagString) throws LiquibaseException {
        LockService lockService = LockServiceFactory.getInstance().getLockService(database);
        lockService.waitForLock();

        try {
            ChangeLogHistoryServiceFactory.getInstance().getChangeLogService(database).generateDeploymentId();

            checkLiquibaseTables(false, null, new Contexts(),
                new LabelExpression());
            getDatabase().tag(tagString);
        } finally {
            try {
                lockService.releaseLock();
            } catch (LockException e) {
                LOG.severe(LogType.LOG, MSG_COULD_NOT_RELEASE_LOCK, e);
            }
        }
    }
'Tags' the database for future rollback