[GENERAL] Indexes on individual columns of composite primary key

[Dan Halbert]

I have a table with four columns. Three of those columns are defined as the 
composite primary key. Does it make sense to create indexes on any or all of 
those three columns individually for performance reasons? PG does let me create 
the indexes. But perhaps it's redundant, since there's an implicitly-created 
index for the composite primary key.
 
Thanks,
Dan