Postgresql snowflake id generator

snowflake-id-generator.sql

create schema shard_1;
create sequence shard_1.global_id_sequence;

CREATE OR REPLACE FUNCTION shard_1.id_generator(OUT result bigint) AS $$
DECLARE
    seq_len int := 14;
    shard_len int := 1;
    seq_max bigint := pow(2, seq_len);

    -- 2022-08-08
    our_epoch bigint := 1659888000000;
    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('shard_1.global_id_sequence') % seq_max INTO seq_id;

    SELECT FLOOR(EXTRACT(EPOCH FROM clock_timestamp()) * 1000) INTO now_millis;

    result := (now_millis - our_epoch) << (seq_len + shard_len);
    result := result | (shard_id << seq_len);
    result := result | (seq_id);
END;
$$ LANGUAGE PLPGSQL;

Notice: this only support generating seq_max id in one millisecond, otherwise, the id will be duplicated, for this example, the seq_max is 16384