Обсуждение: Force 8.2 initdb to rename pg_database/pg_class minxid columns?

Yesterday I wrote:
> * On successful completion, the cutoff XID is stored in
> pg_class.relvacuumxid, and pg_database.datvacuumxid is updated
> if appropriate.  (The minxid columns are now useless, but unless there
> is another reason to force initdb before 8.2, I'm inclined to leave them
> there and unused.  We can remove 'em in 8.3.)

After a closer look I am thinking that maybe we should go ahead and
replace relvacuumxid/relminxid and datvacuumxid/datminxid by single
columns named relfrozenxid and datfrozenxid respectively.  The reason
is that our documentation has for a long time recommended
SELECT datname, age(datfrozenxid) FROM pg_database;

as a good way to check for databases approaching wraparound.
(In fact it still does ... apparently Alvaro didn't bother to update 
maintenance.sgml when he redid that code.)

I don't know how many people might have such queries embedded in
maintenance scripts, but any who do will find their scripts broken by
8.2 as it now stands.  Which is a bit silly considering that the
proposed patch will be maintaining a column having exactly the
longstanding definition of datfrozenxid:
      All rows inserted by transaction IDs before this one have been      relabeled with a permanent (<quote>frozen</>)
transactionID in this      database.
 

I prefer to avoid forcing initdb in late beta, because it causes extra
work for our long-suffering beta testers, but at the moment I'm thinking
this is worth fixing now rather than later.  Comments?
        regards, tom lane

On Thu, Nov 02, 2006 at 05:22:39PM -0500, Tom Lane wrote:
> I prefer to avoid forcing initdb in late beta, because it causes extra
> work for our long-suffering beta testers, but at the moment I'm thinking
> this is worth fixing now rather than later.  Comments?

Given that the column name change entails backwards incompatibility
for many users, and the change no longer signifies an actual change
to underlying functionality, though, it seems worth the pain to me.

A

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Andrew Sullivan  | ajs@crankycanuck.ca
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