I made this custom code that makes Comment into Review with star-rating. The star is saved as comment_karma.

In the Product Archive page, I want to show text like this: "25 people 5-starred this" in each thumbnail.

I can easily get those data with get_comments(). But I'm afraid it will put a heavy load on the server since comment_karma column isn't INDEX.

So, will adding INDEX improves the performance? Is it safe?

Thanks