Someone recently asked me if there was a way to tell which table(s) are slated for VACUUM at the next autovacuum cycle. I couldn’t find any results after a short search on Google, so I decided to come up with my own query. According to source, a table is slated for vacuum when threshold = vac_base_thresh + vac_scale_factor * reltuples. With this knowledge, a simple query to determine tables requiring an autovacuum would be:

SELECT c.relname
  FROM pg_stat_all_tables t,
       pg_class c,
      (SELECT setting
         FROM pg_settings
        WHERE name = 'autovacuum_vacuum_threshold') AS avt,
      (SELECT setting
         FROM pg_settings
        WHERE name = 'autovacuum_vacuum_scale_factor') AS avsf
 WHERE c.oid = t.relid
   AND n_dead_tup > avt.setting::numeric + (avsf.setting::numeric * reltuples);


UPDATE 2020-09-02

Note that autovacuum will vacuum/analyze all relations in the list that it built up before napping again. Therefore, if a table becomes eligible for autovacuum while autovacuum is processing a set of relations, that table will not be autovacuumed until the currently-running round of autovacuum finishes and wakes up after sleeping for autovacuum_naptime.