I'm in the process of adding support for asynchronous server-side
prepare to DBD::Pg because I need this for an application which is
part of one of the products of my employer. The basic idea of
operation is that the (...) complexities of the libpq asynchronous
interface should remain hidden in the driver, in other words, that
asychronous prepare requests should transparently happen as part of
the operation of the existing asynchronous interface. My present
implementation works by using a PQsendPrepare-call instead of a
PQprepare call for queries supposed to be executed asynchronously. The
imp_sth->async_status value is then set to '2' to indicate that an
asychronous prepare is in process. This new 'magic value' is then used
by the db_pg_ready subroutine to detect whether an async prepare is
presently in progress and to deal with the result of that and start
the actual query via PQsendQueryPrepared if the prepare has succeeded.
I would be willing (and probably also allowed to) to submit this as
'feature contribution' if there was any interest in it.
