If it's slow, add this to the top of the file:
EXPLAIN (ANALYZE, COSTS, VERBOSE, BUFFERS, FORMAT JSON)
:!psql -qAt -d db_name -f % | pbcopy
Paste into http://tatiyants.com/pev/#/plans/new and delete the trailing line to make it valid JSON:
Time: 1111.111 ms (00:01.111)
The output is an interactive visualization that makes it easy to identify which parts of the query are slowest, largest, and costliest.