Re: [HACKERS] 9.4.1 -> 9.4.2 problem: could not access status of transaction 1

On Fri, Jun 12, 2015 at 7:27 PM, Steve Kehlet <steve(dot)kehlet(at)gmail(dot)com> wrote:
> 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?

As long as you see only a modest number of files in
pg_multixact/members, you're OK. But in theory, until that emergency
autovacuuming finishes, there's nothing keeping that directory from
wrapping around.

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