Trucos SQL utiles en Postgres

conocer el tamaño de las bases de datos
select pg_database_size(pg_database.datname)) AS size FROM pg_database;

ver consultas en ejecucion
select pg_class.relname, pg_locks.transactionid, pg_locks.mode, pg_locks.granted as "g",
substr(pg_stat_activity.current_query,1,30), pg_stat_activity.query_start,
age(now(),pg_stat_activity.query_start) as "age", pg_stat_activity.procpid
from pg_stat_activity,pg_locks
left outer join pg_class on
(pg_locks.relation = pg_class.oid)
where pg_locks.pid=pg_stat_activity.procpid
order by query_start;