Re: MultiXact member wraparound protections are now enabled

On Fri, Jul 24, 2015 at 09:14:09PM -0400, Peter Eisentraut wrote:
> On 7/22/15 4:45 PM, Robert Haas wrote:
> > But it seemed to me that this could be rather confusing. I thought it
> > would be better to be explicit about whether the protections are
> > enabled in all cases. That way, (1) if you see the message saying
> > they are enabled, they are enabled; (2) if you see the message saying
> > they are disabled, they are disabled; and (3) if you see neither
> > message, your version does not have those protections.
>
> But this is not documented, AFAICT, so I don't think anyone is going to
> be able to follow that logic. I don't see anything in the release notes
> saying, look for this message to see how this applies to you, or whatever.

I supported inclusion of the message, because it has good potential to help
experts studying historical logs to find the root cause of data corruption.
The complex histories of clusters showing corruption from this series of bugs
have brought great expense to the task of debugging new reports. Given a
cluster having full mxact wraparound protections since last corruption-free
backup (or since initdb), one can rule out some causes.