Checking for missing indexes
Once we are done with the first three steps, it is important to take a look at performance in general. As I have continually stated throughout this book, missing indexes are fully responsible for super-bad database performance, so whenever we face a slow system, it is recommended that we check for missing indexes and deploy whatever is needed.
Usually, customers ask us to optimize the RAID level, tune the kernel, or do some other fancy stuff. In reality, these complicated requests often boil down to a handful of missing indexes. In my opinion, it always makes sense to spend some extra time just checking whether all of the 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 that you face.
Here is my favorite query to get an impression of where an index may be missing:
SELECT schemaname, relname, seq_scan, seq_tup_read, ...