From: | Matthias Apitz <guru(at)unixarea(dot)de> |
---|---|
To: | pgsql-general(at)lists(dot)postgresql(dot)org |
Subject: | lifetime of the old CTID |
Date: | 2022-07-05 07:51:19 |
Message-ID: | 20220705075119.GA23@sh4-5.1blu.de |
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Lists: | pgsql-general |
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(at)unixarea(dot)de, http://www.unixarea.de/ +49-176-38902045
Public GnuPG key: http://www.unixarea.de/key.pub
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