The checking for calls to volatile functions in the COPY FROM ... WHERE
expression was treating all WHERE clauses as if containing such calls.
While that does not produce incorrect results, this disables batching
which may result in significant performance regression.

Discussion: https://www.postgresql.org/message-id/flat/CALAY4q_DdpWDuB5-Zyi-oTtO2uSk8pmy+dupiRe3AvAc++1imA@mail.gmail.com