How to do it…

We add conditional commands to vartest.sql resulting in the following script:

SELECT schemaname
, relname
, n_dead_tup
, n_live_tup
, n_dead_tup > 0 AS needs_vacuum
FROM pg_stat_user_tables
ORDER BY n_dead_tup DESC
LIMIT 1
\gset
\if :needs_vacuum
\qecho Running VACUUM on table :"relname" in schema :"schemaname"
\qecho Rows before: :n_dead_tup dead, :n_live_tup live
VACUUM ANALYZE :schemaname.:relname;
\qecho Waiting 1 second...
SELECT pg_sleep(1);
SELECT n_dead_tup AS n_dead_tup_now
,      n_live_tup AS n_live_tup_now
FROM pg_stat_user_tables
WHERE schemaname = :'schemaname' AND relname = :'relname'
\gset
\qecho Rows after: :n_dead_tup_now dead, :n_live_tup_now live
\else
\qecho Skipping VACUUM on table :"relname" in schema :"schemaname"
\endif