PG Serializability

Session 1
====

Will sleep for 5 seconds giving you time to launch TXN2.

DROP TABLE foo;

CREATE TABLE foo(x) AS
  VALUES (1),(2),(3);


CREATE OR REPLACE FUNCTION test_foo_has_null()
RETURNS bool
AS
$BODY$
  BEGIN
    IF (SELECT count(*) = 0 FROM foo WHERE x IS NULL) THEN
      PERFORM pg_sleep(5);
      RETURN false;
    ELSE
      RETURN true;
    END IF;
  END;
$BODY$
LANGUAGE 'plpgsql';

BEGIN;
  SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
  SELECT test_foo_has_null();
END;

Session 2
====

BEGIN;
  SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
  INSERT INTO foo(x) VALUES (null);
END;