-- List the work_mem setting of each worker database
SELECT run_command_on_workers($cmd$ SHOW work_mem; $cmd$);

-- Get the estimated row count for a distributed table by summing the
-- estimated counts of rows for each shard.
SELECT sum(result::bigint) AS estimated_count
  FROM run_command_on_shards(
    'my_distributed_table',
    $cmd$
      SELECT reltuples
        FROM pg_class c
        JOIN pg_catalog.pg_namespace n on n.oid=c.relnamespace
       WHERE (n.nspname || '.' || relname)::regclass = '%s'::regclass
         AND n.nspname NOT IN ('citus', 'pg_toast', 'pg_catalog')
    $cmd$
  );

-- note we're using a hard-coded date rather than
-- a function such as "now()" because the query will
-- run at slightly different times on each replica
SELECT run_command_on_placements(
  'my_distributed_table',
  $cmd$
    UPDATE %s SET updated_at = '2017-01-01';
  $cmd$
);

-- Suppose we have two distributed tables
CREATE TABLE little_vals (key int, val int);
CREATE TABLE big_vals    (key int, val int);
SELECT create_distributed_table('little_vals', 'key');
SELECT create_distributed_table('big_vals',    'key');
-- We want to synchronize them so that every time little_vals
-- are created, big_vals appear with double the value
--
-- First we make a trigger function, which will
-- take the destination table placement as an argument
CREATE OR REPLACE FUNCTION embiggen() RETURNS TRIGGER AS $$
  BEGIN
    IF (TG_OP = 'INSERT') THEN
      EXECUTE format(
        'INSERT INTO %s (key, val) SELECT ($1).key, ($1).val*2;',
        TG_ARGV[0]
      ) USING NEW;
    END IF;
    RETURN NULL;
  END;
$$ LANGUAGE plpgsql;
-- Next we relate the co-located tables by the trigger function
-- on each co-located placement
SELECT run_command_on_colocated_placements(
  'little_vals',
  'big_vals',
  $cmd$
    CREATE TRIGGER after_insert AFTER INSERT ON %s
      FOR EACH ROW EXECUTE PROCEDURE embiggen(%L)
  $cmd$
);