Non-sequential Primary Key performance in PostgreSQL 9.3
I have 3 solutions for you:
Direct reference of sequence and using concat
One possible solution is to reference the seqence in insert statement directly and prepend your node-id. A similar question including answer you can find here:
https://stackoverflow.com/a/17925601/4206293
Using a UUID
Another possible solution is, if you don't need you node-id in the primary-key field, you can use the uuid-ossp extension which provides the type uuid and the functions to generate uuids: http://www.postgresql.org/docs/9.4/static/uuid-ossp.html
Use a trigger for these solutions
For both solutions: you can use a trigger to set the primary key.
Example:
-- table
CREATE TABLE test(
   id character varying(10) NOT NULL,
  &quot;name&quot; character varying,
   CONSTRAINT idx_pk PRIMARY KEY (id)
);

-- seqence
CREATE SEQUENCE test_seq
  INCREMENT 1
  MINVALUE 1
  MAXVALUE 9223372036854775807
  START 1
  CACHE 1;

-- Create Function
CREATE OR REPLACE FUNCTION insert_trigger() 
RETURNS TRIGGER    
AS $$
BEGIN
   NEW.id := '100' || nextval('test_seq')::TEXT;
   RETURN NEW;
END;
$$ LANGUAGE 'plpgsql';

-- add Trigger
CREATE TRIGGER insert_table_trigger
BEFORE INSERT ON pkTable
FOR EACH ROW EXECUTE PROCEDURE insert_trigger();

If you now insert a value in the table
INSERT INTO test (name) VALUES ('test text');

you get your primary key '1001'
Using MINVALUE and MAXVALUE
Another way is you use the MINVALUE and MAXVALUE of SEQUENCE to define an numeric space:
CREATE SEQUENCE node100_seq
  INCREMENT 1
  MINVALUE 100000000000
  MAXVALUE 100999999999
  START 100000000000
  CACHE 1;

CREATE SEQUENCE node200_seq
  INCREMENT 1
  MINVALUE 200000000000
  MAXVALUE 200999999999
  START 200000000000
  CACHE 1;