Visual explain
Complicated query plans can be difficult to read, with only the indentation level suggesting how nodes that fit into one another are connected. One way to help visualize complicated plans is to graph them using visual explain, a feature available in the pgAdmin III tool: http://www.pgadmin.org/.
Seeing how the nodes fit together for the more complicated structures like multi-level joins is extremely valuable for learning how they work. One useful bit of trivia for the graphic display used: when you see lines connecting nodes in the plan, their thickness is proportional to how costly that section of the plan is. You can get an idea where the parts taking a while to execute are just by looking for the wide lines; the thin ones aren't contributing as heavily to the query runtime.
