There was a prior email dev thread about PubSub ordering key[1] but that was in reference to reads. It should be possible to support pubsub Write with ordering key. We might be able to have users supply a serializable function to extra the ordering key from each message, for example?

 [1] http://mail-archives.apache.org/mod_mbox/beam-dev/202010.mbox/%3CCAGAbUe93TcwnC+fyAkE3MmtNANi-oFUXPQbg-gDyP6oB8eLTkA@mail.gmail.com%3E

Imported from Jira BEAM-13148. Original Jira may contain additional context.
Reported by: egalpin.