back-branch multixact fixes & 9.5 alpha/beta: schedule

Hi,

I think we have consensus that we should proceed with releasing fixes
for the known multixact bugs in two stages:

- One set of minor releases with the fixes that we have now, to undo
the damage caused by 9.4.2 and still present in 9.4.3. These changes
will force immediate anti-wraparound vacuums for some users in order
to repair bogus relminmxid, datminmxid, and control-file
oldestMultiXid values. They will also fix failure-to-start problems
confirmed to exist in 9.4.2 and suspected problems with crash recovery
and recovery of an online backup.

- Another set of minor releases with the changes that Andres is
working on to add WAL-logging for multixact truncation. I suppose
this will require the usual dance of upgrading the standby first and
then the master afterwards; there are details I'm not clear on yet
here. This will fix other problems with recovery that are not new in
9.4.2 but go all the way back to 9.3.0.

In addition, it seems abundantly clear that everyone is very eager to
get some sort of 9.5 version out the door - if not a beta, then an
alpha. I am still a bit concerned that's premature, but, on the other
hand, time is passing and at least some issues are getting dealt with
in the meantime, so... that's something.

So, when shall we do all of this releasing? It seems like we could do
stage-one of the multixact fixing this week, and then figure out how
to do the other stuff after PGCon. Alternatively, we can let the
latest round of changes that are already in the tree settle until
after PGCon, and plan a release for stage-one of the multixact fixing
then. Whichever we pick, we then need to figure out the timetable for
the rest of it.

Thanks,

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company