Re: preserving forensic information when we freeze

On 2013-05-28 09:39:13 -0700, Josh Berkus wrote:
> On 05/28/2013 06:21 AM, Robert Haas wrote:
> > As a general statement, I view this work as something that is likely
> > needed no matter which one of the "remove freezing" approaches that
> > have been proposed we choose to adopt.  It does not fix anything in
> > and of itself, but it (hopefully) removes an objection to the entire
> > line of inquiry.
> 
> Agreed.  I have some ideas on how to reduce the impact of freezing as
> well (of course), and the description of your approach certainly seems
> to benefit them, especially as it removes the whole "forensic
> information" objection.
> 
> One question though: if we're not removing the xmin, how do we know the
> maximum xid to which we can prune clog?  I can imagine several ways
> given your approach.

Simply don't count xids which are frozen. Currently we ignore an xid
because its a special value, after this because the tuple has a certain
hint bit (combination) set.

Greetings,

Andres Freund

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