Performance of a SELECT FOR UPDATE may be quite distinct from the
non-UPDATE version of the query, so treat all of the FOR UPDATE clause
as being significant for distinguishing queries.

Andrew Gierth and Vik Fearing, reviewed by Sergei Kornilov, Thomas
Munro, Tom Lane

Discussion: https://postgr.es/m/87h8e4hfwv.fsf@news-spur.riddles.org.uk