set all tables clustered by PK if there is one and no clustering index is set

setcluster.sql

do $$

declare
        rec record;
        cmd text;
begin
        for rec in 
            select n.nspname, rc.relname as tbl, ic.relname as idx
            from pg_index i 
                 join pg_class ic
                      on i.indexrelid = ic.oid
                 join pg_class rc
                      on i.indrelid = rc.oid
                 join pg_namespace n
                      on rc.relnamespace = n.oid
            where i.indisprimary 
                  and rc.relkind = 'r'
                  and n.nspname <> 'information_schema'
                  and n.nspname !~ '^pg_'
                  and rc.oid not in (select indrelid 
                                     from pg_index
                                     where indisclustered)
         loop
                cmd := 'ALTER TABLE ' || quote_ident(rec.nspname) ||
                      '.' || quote_ident(rec.tbl) || ' CLUSTER ON ' ||
                      quote_ident(rec.idx);
                -- raise notice 'CMD: %', cmd;
                execute cmd;
         end loop;

end;

$$;