Here we imply a recursive definition and custom rules for each level. Maybe we repeat each stage of validation rules for the nested structures but with different sets of rules.

In the Java world, I imagine an exception thrown when the socket gets closed or the famous broken pipe exception appears.

Good question to guide the experience of solving errors from the client standpoint.

Practical highlights in my opinion:

• It's important to know about data padding in PG.
• Be conscious when modelling data tables about columns ordering, but don't be pure-school and do it in a best-effort basis.
• Gains up to 25% in wasted storage are impressive but always keep in mind the scope of the system. For me, gains are not worth it in the short-term. Whenever a system grows, it is possible to migrate data to more storage-efficient tables but mind the operative burder.

Here follows my own commands on trying the article points. I added - pg_column_size(row()) on each projection to have clear absolute sizes.

-- How does row function work?

SELECT pg_column_size(row()) AS empty,
       pg_column_size(row(0::SMALLINT)) AS byte2,
       pg_column_size(row(0::BIGINT)) AS byte8,
       pg_column_size(row(0::SMALLINT, 0::BIGINT)) AS byte16,
       pg_column_size(row(''::TEXT)) AS text0,
       pg_column_size(row('hola'::TEXT)) AS text4,
       0 AS term
;

-- My own take on that

SELECT pg_column_size(row()) AS empty,
       pg_column_size(row(uuid_generate_v4())) AS uuid_type,
       pg_column_size(row('hola mundo'::TEXT)) AS text_type,
       pg_column_size(row(uuid_generate_v4(), 'hola mundo'::TEXT)) AS uuid_text_type,
       pg_column_size(row('hola mundo'::TEXT, uuid_generate_v4())) AS text_uuid_type,
       0 AS term
;

CREATE TABLE user_order (
  is_shipped    BOOLEAN NOT NULL DEFAULT false,
  user_id       BIGINT NOT NULL,
  order_total   NUMERIC NOT NULL,
  order_dt      TIMESTAMPTZ NOT NULL,
  order_type    SMALLINT NOT NULL,
  ship_dt       TIMESTAMPTZ,
  item_ct       INT NOT NULL,
  ship_cost     NUMERIC,
  receive_dt    TIMESTAMPTZ,
  tracking_cd   TEXT,
  id            BIGSERIAL PRIMARY KEY NOT NULL
);

SELECT a.attname, t.typname, t.typalign, t.typlen
  FROM pg_class c
  JOIN pg_attribute a ON (a.attrelid = c.oid)
  JOIN pg_type t ON (t.oid = a.atttypid)
 WHERE c.relname = 'user_order'
   AND a.attnum >= 0
 ORDER BY a.attnum;

-- What is it about pg_class, pg_attribute and pg_type tables? For future investigation.

-- SELECT sum(t.typlen)
-- SELECT t.typlen
SELECT a.attname, t.typname, t.typalign, t.typlen
  FROM pg_class c
  JOIN pg_attribute a ON (a.attrelid = c.oid)
  JOIN pg_type t ON (t.oid = a.atttypid)
 WHERE c.relname = 'user_order'
   AND a.attnum >= 0
 ORDER BY a.attnum
;

-- Whoa! I need to master mocking data directly into db.

INSERT INTO user_order (
    is_shipped, user_id, order_total, order_dt, order_type,
    ship_dt, item_ct, ship_cost, receive_dt, tracking_cd
)
SELECT true, 1000, 500.00, now() - INTERVAL '7 days',
       3, now() - INTERVAL '5 days', 10, 4.99,
       now() - INTERVAL '3 days', 'X5901324123479RROIENSTBKCV4'
  FROM generate_series(1, 1000000);

-- New item to learn, pg_relation_size. 

SELECT pg_relation_size('user_order') AS size_bytes,
       pg_size_pretty(pg_relation_size('user_order')) AS size_pretty;

SELECT * FROM user_order LIMIT 1;

SELECT pg_column_size(row(0::NUMERIC)) - pg_column_size(row()) AS zero_num,
       pg_column_size(row(1::NUMERIC)) - pg_column_size(row()) AS one_num,
       pg_column_size(row(9.9::NUMERIC)) - pg_column_size(row()) AS nine_point_nine_num,
       pg_column_size(row(1::INT2)) - pg_column_size(row()) AS int2,
       pg_column_size(row(1::INT4)) - pg_column_size(row()) AS int4,
       pg_column_size(row(1::INT2, 1::NUMERIC)) - pg_column_size(row()) AS int2_one_num,
       pg_column_size(row(1::INT4, 1::NUMERIC)) - pg_column_size(row()) AS int4_one_num,
       pg_column_size(row(1::NUMERIC, 1::INT4)) - pg_column_size(row()) AS one_num_int4,
       0 AS term
;

SELECT pg_column_size(row(''::TEXT)) - pg_column_size(row()) AS empty_text,
       pg_column_size(row('a'::TEXT)) - pg_column_size(row()) AS len1_text,
       pg_column_size(row('abcd'::TEXT)) - pg_column_size(row()) AS len4_text,
       pg_column_size(row('abcde'::TEXT)) - pg_column_size(row()) AS len5_text,
       pg_column_size(row('abcdefgh'::TEXT)) - pg_column_size(row()) AS len8_text,
       pg_column_size(row('abcdefghi'::TEXT)) - pg_column_size(row()) AS len9_text,
       0 AS term
;

SELECT pg_column_size(row(''::TEXT, 1::INT4)) - pg_column_size(row()) AS empty_text_int4,
       pg_column_size(row('a'::TEXT, 1::INT4)) - pg_column_size(row()) AS len1_text_int4,
       pg_column_size(row('abcd'::TEXT, 1::INT4)) - pg_column_size(row()) AS len4_text_int4,
       pg_column_size(row('abcde'::TEXT, 1::INT4)) - pg_column_size(row()) AS len5_text_int4,
       pg_column_size(row('abcdefgh'::TEXT, 1::INT4)) - pg_column_size(row()) AS len8_text_int4,
       pg_column_size(row('abcdefghi'::TEXT, 1::INT4)) - pg_column_size(row()) AS len9_text_int4,
       0 AS term
;

SELECT pg_column_size(row(1::INT4, ''::TEXT)) - pg_column_size(row()) AS int4_empty_text,
       pg_column_size(row(1::INT4, 'a'::TEXT)) - pg_column_size(row()) AS int4_len1_text,
       pg_column_size(row(1::INT4, 'abcd'::TEXT)) - pg_column_size(row()) AS int4_len4_text,
       pg_column_size(row(1::INT4, 'abcde'::TEXT)) - pg_column_size(row()) AS int4_len5_text,
       pg_column_size(row(1::INT4, 'abcdefgh'::TEXT)) - pg_column_size(row()) AS int4_len8_text,
       pg_column_size(row(1::INT4, 'abcdefghi'::TEXT)) - pg_column_size(row()) AS int4_len9_text,
       0 AS term
;

SELECT pg_column_size(row()) - pg_column_size(row()) AS empty_row,
       pg_column_size(row(''::TEXT)) - pg_column_size(row()) AS no_text,
       pg_column_size(row('a'::TEXT)) - pg_column_size(row()) AS min_text,
       pg_column_size(row(1::INT4, 'a'::TEXT)) - pg_column_size(row()) AS two_col,
       pg_column_size(row('a'::TEXT, 1::INT4)) - pg_column_size(row()) AS round4;

SELECT pg_column_size(row()) - pg_column_size(row()) AS empty_row,
       pg_column_size(row(1::SMALLINT)) - pg_column_size(row()) AS int2,
       pg_column_size(row(1::INT)) - pg_column_size(row()) AS int4,
       pg_column_size(row(1::BIGINT)) - pg_column_size(row()) AS int8,
       pg_column_size(row(1::SMALLINT, 1::BIGINT)) - pg_column_size(row()) AS padded,
       pg_column_size(row(1::INT, 1::INT, 1::BIGINT)) - pg_column_size(row()) AS not_padded;

SELECT a.attname, t.typname, t.typalign, t.typlen
  FROM pg_class c
  JOIN pg_attribute a ON (a.attrelid = c.oid)
  JOIN pg_type t ON (t.oid = a.atttypid)
 WHERE c.relname = 'user_order'
   AND a.attnum >= 0
 ORDER BY t.typlen DESC;

DROP TABLE user_order;

CREATE TABLE user_order (
  id            BIGSERIAL PRIMARY KEY NOT NULL,
  user_id       BIGINT NOT NULL,
  order_dt      TIMESTAMPTZ NOT NULL,
  ship_dt       TIMESTAMPTZ,
  receive_dt    TIMESTAMPTZ,
  item_ct       INT NOT NULL,
  order_type    SMALLINT NOT NULL,
  is_shipped    BOOLEAN NOT NULL DEFAULT false,
  order_total   NUMERIC NOT NULL,
  ship_cost     NUMERIC,
  tracking_cd   TEXT
);

-- And, what about other varying size types as JSONB?

SELECT pg_column_size(row('{}'::JSONB)) - pg_column_size(row()) AS empty_jsonb,
       pg_column_size(row('{}'::JSONB, 0::INT4)) - pg_column_size(row()) AS empty_jsonb_int4,
       pg_column_size(row(0::INT4, '{}'::JSONB)) - pg_column_size(row()) AS int4_empty_jsonb,
       pg_column_size(row('{"a": 1}'::JSONB)) - pg_column_size(row()) AS basic_jsonb,
       pg_column_size(row('{"a": 1}'::JSONB, 0::INT4)) - pg_column_size(row()) AS basic_jsonb_int4,
       pg_column_size(row(0::INT4, '{"a": 1}'::JSONB)) - pg_column_size(row()) AS int4_basic_jsonb,
       0 AS term;