Re: pg_multixact not getting truncated

On Wed, Nov 19, 2014 at 4:16 PM, Josh Berkus <josh(at)agliodbs(dot)com> wrote:
> On 11/19/2014 01:03 PM, Alvaro Herrera wrote:
>> Josh Berkus wrote:
>>> On 11/12/2014 06:57 PM, Alvaro Herrera wrote:
>>>>> How did template0 even get a MultiXact? That sounds like they're really abusing the template databases. :( (Do keep in mind that MXID 1 is a special value.)
>>>> No, it's normal -- template0 does not have a multixact in any tuple's
>>>> xmax, but datminxid is set to the value that is current when it is
>>>> frozen.
>>>
>>> So, to follow up on this: it seems to me that we shouldn't be requiring
>>> freezing for databases where allowconn=false. This seems like a TODO to
>>> me, even possibly a backpatchable bug fix.
>>
>> Why do we need this for pg_multixact but not for pg_clog?
>
> I think we want it for both.

So that we can have two ways to lose data?

Forbidding connections to a database doesn't prevent XID or MXID wraparound.

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