lifetime of the old CTID

[Matthias Apitz <guru@xxxxxxxxxxx>]

Hello,

We're using the SQL function currtid2() to get the new CTID of a row
when this was UPDATEd.

Investigating cases of failing updates, it turns out that the old CTID
has only a limited lifetime; one can check this with SQL:

sisis=# select ctid, d01gsi from d01buch where d01gsi = '0240564';
    ctid    |           d01gsi            
------------+-----------------------------
 (29036,11) | 0240564

now I update the row and afterwards pick up the new CTID based on the
old one (29036,11):

sisis=# UPDATE d01buch set d01ort='Wolfratshausen' where d01gsi='0240564';
UPDATE 1
sisis=# SELECT currtid2('d01buch'::text, '(29036,11)'::tid);
 currtid2  
-----------
 (29036,7)

Now I go and pick up a coffe in our kitchen and check again:

sisis=# SELECT currtid2('d01buch'::text, '(29036,11)'::tid);
  currtid2  
------------
 (29036,11)

i.e. the function now only returns it argument. and not the new CTID
anymore.

Why is this? And what triggers exactly that the old CTID can't be used
anymore?

Thanks

	matthias
-- 
Matthias Apitz, ✉ guru@xxxxxxxxxxx, http://www.unixarea.de/ +49-176-38902045
Public GnuPG key: http://www.unixarea.de/key.pub