Checking private (non shared) memory usage for Postgresql connection (PID)

Create function:

 CREATE OR REPLACE FUNCTION pid_mem_usage( pid integer)
 RETURNS integer AS $$
 DECLARE l_command TEXT; res integer;
 BEGIN
  SET client_min_messages = 'error';
  l_command  := ' cat /proc/' || pid || '/smaps | grep "^Private" | awk ''{a+=$2}END{print a * 1024}'' ';
  raise notice '%',l_command;
  execute 'create temp table if not exists z (a int) ';
  execute 'copy z from program ' || quote_literal(l_command);
  execute 'select sum(a) from z' into res;
  execute 'truncate z';
 RETURN res;
 END;
 $$ LANGUAGE plpgsql;

Sample usage:

select pid_mem_usage(pid),pid,usename,backend_start,xact_start,
query from pg_stat_activity  order by 1 desc limit 25;

Based on from https://www.depesz.com/2012/06/09/how-much-ram-is-postgresql-using/