target_session_attrs=read-only is only supported on libpq >= 14

[steve-chavez]

Problem

The docs instruct to add target_session_attrs=read-only to the db-uri, but this will fail on an instance with libpq < 14:

"Failed to query the role settings. {"code":"PGRST000","details":"invalid target_session_attrs value: \"read-only\"\n","hint":null,"message":"Database connection error. Retrying the connection."}"

(uses the ubuntu-aarch64 release)

This happens because target_session_attrs only accepts read-only starting from libpq 14. target_session_attrs only supports read-write on libpq13, see https://www.postgresql.org/docs/13/libpq-connect.html#LIBPQ-CONNECT-TARGET-SESSION-ATTRS.

Solution

Warn about this limitation on the docs.