Just wanted to report that I rolled back my VM to where it was with 9.4.2 installed and it wouldn't start. I installed 9.4.4 and now it starts up just fine:
> 2015-06-12 16:05:58 PDT [6453]: [1-1] LOG: database system was shut down at 2015-05-27 13:12:55 PDT
> 2015-06-12 16:05:58 PDT [6453]: [2-1] LOG: MultiXact member wraparound protections are disabled because oldest checkpointed MultiXact 1 does not exist on disk
> 2015-06-12 16:05:58 PDT [6457]: [1-1] LOG: autovacuum launcher started
> 2015-06-12 16:05:58 PDT [6452]: [1-1] LOG: database system is ready to accept connections
> done
> server started
And this is showing up in my serverlog periodically as the emergency autovacuums are running:
> 2015-06-12 16:13:44 PDT [6454]: [1-1] LOG: MultiXact member wraparound protections are disabled because oldest checkpointed MultiXact 1 does not exist on disk
**Thank you Robert and all involved for the resolution to this.**
> With the fixes introduced in this release, such a situation will result in immediate emergency autovacuuming until a correct oldestMultiXid value can be determined
Okay, I notice these vacuums are of the "to prevent wraparound" type (like VACUUM FREEZE), that do hold locks preventing ALTER TABLEs and such. Good to know, we'll plan our software updates accordingly.
Is there any risk until these autovacuums finish?