[jacques_chester]

> I think it was more that forks just get ignored

They call out a number of forks that do quite nicely. I work for Pivotal, which sponsors Greenplum. Companies pay handsomely for the capabilities it brings to the table.

But they are right that rebasing is a nightmare. My understanding (possibly wrong) is that the broad selection of APIs that make an extension-only approach did not appear in PostgreSQL until more recent versions -- anyone who forked earlier (such as Greenplum) have to first catch up and then migrate.

I do know that the Greenplum team have decided to catch up until they are working against mainline. It is, as you might imagine, a slow process: rebasing millions of lines of code a release at a time is not the easiest task on earth. But maintaining a fork will, in the long run, be harder.