I am doing a `group by` on a table with ~ 3 million rows, the code is
simply `select A, B, C, D,E count(1) from t group by A, B, C, D, E order by
6`, it takes ~ 3 minutes for this operation and there are ~ 500 rows
returned. So, to speed this up, should I add a composite index on A, B, C,
D, E or there are some parameters in postgresql.conf I can tweak, I am new
to postgres, all the parameters in postgresql.conf are the default.