On 10/1/2007 3:07 AM, Tom Lane wrote:
> "Marko Kreen" <markokr at gmail.com> writes:
>> On 10/1/07, Tom Lane <tgl at sss.pgh.pa.us> wrote:
>>> I'm having quite a bit of a problem with the above.  Why is
>>> InvalidTransactionId mapped to MAX_TXID, which presumably is part of the
>>> normal XID rotation and hence only larger than half of the universe,
>>> when the other special XIDs map as themselves?
> 
>> Because InvalidTransactionId is supposed to be always invisible,
>> but others always visible?  And we don't want to add epoch to
>> any of them.
> 
> Well, all three of the "special" xids need to be epoch-independent.
> I still think this is either bad design or an outright bug.

The txid code should never see any invalid XID. All the current paths in 
it take xid's from sources where they are not invalid. So it would be 
safe to not map it at all, but rather bail out with an error should 
someone ever add that.

> 
>> I used StringInfo as it was only buffer tool available from backend...
> 
> Maybe, but don't be too surprised if it breaks under you ...

The xxid code this all was coming from had its own buffer management. It 
may be safer to keep using that.


Jan

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