Once you are done with the first three steps, it is important to take a look at performance in general. As I kept stating throughout this book, missing indexes are super important to achieve super bad performance. So, whenever you are facing a slow system, is it recommended to check for missing indexes and deploy whatever is needed.
Usually customers ask you to optimize the RAID level, tune the kernel, or some other fancy stuff. In reality, those complicated requests often boil down to a handful of missing indexes. By my judgment, it always makes sense to spend some extra time on just checking whether all desired indexes are there. Checking for missing indexes is neither hard nor time consuming, so it should be done all the time regardless of the kind of performance problem you are facing.
Here is my favorite query to get an impression of where an index might be missing:
SELECT schemaname...