Database performance for polymorphic associations under high load

Hey guys,

I’ve been thinking lately about polymorphic associations, and I
wonder: is there a noticeable or tangible performance “hit” from doing
polymorphic associations when you’ve got your database under really
high query load?

So for example, maybe I have a “message” model, a “user” model and an
“administrator” model, without any subclassing or STI going on.
Message has a polymorphic interface called “message_author”, and both
“User” and “Administrator” use it. Say there wind up being ~1 million
messages in that message table. Assuming everything’s properly
indexed, do polymorphic associations add any significant overhead to
conducting database queries?

Thanks guys, appreciate the input.

I would stay away from polymorphic as there is no way to enforce DB FK

That’s been my “official” stance for a while as well, and I’m fully
aware of that - but I’m also wondering about its performance, so I can
get a better perspective of the “full picture”, if you follow my

Still, your point is quite valid and has been taken under advisement.
Thank you.

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