pg_update_batch_test.sql

CREATE TABLE test (
  id BIGINT GENERATED ALWAYS AS IDENTITY NOT NULL PRIMARY KEY,
  data_field VARCHAR(255) NOT NULL
);

INSERT INTO test(data_field) SELECT(i::text) FROM generate_series(1,10000) as t(i);

-- repeat several times
WITH candidate_rows AS (
   SELECT id
   FROM test
   WHERE data_field <> 'updated'
   LIMIT 1200
   FOR UPDATE NOWAIT
 ), update_rows AS (
   UPDATE test
   SET data_field = 'updated'
   FROM candidate_rows
   WHERE candidate_rows.id = test.id
   RETURNING test.id
 )
SELECT count(1) FROM update_rows;

DROP TABLE test;