Re: preserving forensic information when we freeze

On Fri, Dec 20, 2013 at 7:51 AM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> On 2013-12-20 07:47:17 -0500, Robert Haas wrote:
>> On Fri, Dec 20, 2013 at 7:22 AM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
>> >> Maybe what we should do is add a function something like
>> >> pg_tuple_header(tableoid, ctid) that returns a record, maybe something
>> >> like (rawxmin xid, rawxmax xid, rawcid cid, infomask int, infomask2
>> >> int, hoff int). Or perhaps some slightly more cooked version of that
>> >> information. And then delete the xmin, xmax, cmin, and cmax system
>> >> columns. That'd save significantly on pg_attribute entries while, at
>> >> the same time, actually providing more information than we do today.
>> >
>> > I was wondering whether we couldn't just pass pg_tuple_header() a whole
>> > row, instead of having the user manually pass in reloid and ctid. I
>> > think that should actually work in the interesting scenarios.
>>
>> I wondered that, too, but it's not well-defined for all tuples. What
>> happens if you pass in constructed tuple rather than an on-disk tuple?
>
> Those should be discernible I think, t_self/t_tableOid won't be set for
> generated tuples.

Hmm. That might work.

I think the immediate problem is to decide whether this patch ought to
make the xmin column display the result of GetXmin() or GetRawXmin().
Thoughts on that?

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