I couldn't find anything in the docs or in the mailing list on this,
but it is something that Oracle appears to do as does MySQL.
The idea, I believe, is to do a quick (hash) string lookup of the
query and if it's exactly the same as another query that has been done
recently to re-use the old parse tree.
It should save the time of doing the parsing of the SQL and looking up
the object in the system tables.
It should probably go through the planner again because values passed
as parameters may have changed. Although, for extra points it could
look at the previous query plan as a hint.
On the surface it looks like an easy enhancement, but what do I know?
I suppose it would benefit mostly those programs that use a lot of
PQexecParams() with simple queries where a greater percentage of the
time is spent parsing the SQL rather than building the execute plan.
What do you think?