@Override
    public void prepare() throws ServiceNotProvidedException, ModuleStartException {
        super.prepare();

        // Override service implementations.

        this.registerServiceImplementation(
            IMetricsQueryDAO.class,
            new PostgreSQLMetricsQueryDAO(jdbcClient, tableHelper));
        this.registerServiceImplementation(
            IAggregationQueryDAO.class,
            new PostgreSQLAggregationQueryDAO(jdbcClient, tableHelper));
    }
PostgreSQL storage enhanced and came from MySQLStorageProvider to support PostgreSQL.
oap-server/server-storage-plugin/storage-jdbc-hikaricp-plugin/src/main/java/org/apache/skywalking/oap/server/storage/plugin/jdbc/postgresql/PostgreSQLStorageProvider.java