CREATE SEQUENCE global_id_sequence;

CREATE OR REPLACE FUNCTION seq_id(OUT result bigint) AS $$
DECLARE
  our_epoch bigint := 1314220021721;
  seq_id bigint;
  now_millis bigint;
  -- the id of this DB shard, must be set for each
  -- schema shard you have - you could pass this as a parameter too
  shard_id int := 1;
BEGIN
  SELECT nextval('global_id_sequence') % 1024 INTO seq_id;

  SELECT FLOOR(EXTRACT(EPOCH FROM clock_timestamp()) * 1000) INTO now_millis;
  result := (now_millis - our_epoch) << 23;
  result := result | (shard_id << 10);
  result := result | (seq_id);
END;
$$ LANGUAGE PLPGSQL;

<!--alter function seq_id(out bigint) owner to postgres;-->

do language plpgsql
$$
begin
update grade set grade = 90 where sno = '20161003';
end
$$