presto-postgresql/src/main/java/io/prestosql/plugin/postgresql/PostgreSqlClient.java/PostgreSqlClient/hstoreColumnMapping
class PostgreSqlClient:    private ColumnMapping hstoreColumnMapping(ConnectorSession session)
    {
        return ColumnMapping.blockMapping(
                varcharMapType,
                varcharMapReadFunction(),
                hstoreWriteFunction(session),
                DISABLE_PUSHDOWN);
    }