Les tables de type pg_toast_xxxx sont lièes à des tables portant des noms humains, voici comment retrouver ces tables:
A partir de pg_class (jointure directe) :

SELECT
  t1.oid            AS oid_table_principale,
  n1.nspname        AS schema_principal,
  t1.relname        AS table_principale,
  t2.oid            AS oid_toast,
  n2.nspname        AS schema_toast,
  t2.relname        AS toast_table
FROM pg_class t1
JOIN pg_namespace n1 ON n1.oid = t1.relnamespace
JOIN pg_class t2     ON t1.reltoastrelid = t2.oid
JOIN pg_namespace n2 ON n2.oid = t2.relnamespace
WHERE t1.relkind = 'r'
  AND t2.relkind = 't'
  AND t2.relname = '<table_toast>';

 

A partir de regclass :
SELECT
  n.nspname   AS schema_principal,
  c.relname   AS table_principale
FROM pg_class c
JOIN pg_namespace n
  ON n.oid = c.relnamespace
WHERE c.reltoastrelid = '<table_toast>'::regclass;

 

Pour les index :

SELECT                                                                       
    n.nspname || '.' || c.relname AS "TABLE PARENT",
    c.relname AS "Nom Table",
    n.nspname AS "Schéma"
FROM pg_class c
JOIN pg_namespace n ON n.oid = c.relnamespace
WHERE c.oid = <pg_toast_id_index>;

 

pg_toast_id_index = identifiant du toast de l'index 

exemple :

table : pg_toast_10455001_index , l'identifiant est 10455001