Hey,
According to 31.18,
http://www.postgresql.org/docs/9.1/static/libpq-threading.html
"PGresult objects are read-only after creation, and so can be passed around
freely between threads."
But PGresult objects are *not* read-only because of existence of
PQsetvalue() described in
http://www.postgresql.org/docs/9.1/static/libpq-misc.html
--
// Dmitriy.