On 1 August 2011 18:36, Robert Haas <robertmhaas@gmail.com> wrote:
> On Mon, Aug 1, 2011 at 1:31 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Dean Rasheed <dean.a.rasheed@gmail.com> writes:
>>> On 1 August 2011 17:49, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>>> Ummm ... I only read the data structure comments, not the code, but I
>>>> don't see where you store the second CTID for an update event?
>>
>>> Ah yes, I forgot to mention that bit. I'm using
>>> &(tuple1.t_data->t_ctid) to get the second CTID from the old tuple. Is
>>> that safe?
>>
>> Hmmmm ... not sure. It seems a bit scary, but on the other hand we
>> should be able to assume that the updating subtransaction hasn't been
>> rolled back (else surely we shouldn't be firing the trigger). So in
>> principle it seems like the t_ctid link can't have been replaced.
>> This will foreclose any ideas about collapsing t_ctid link chains,
>> if anyone had it in mind to do that.
>
> Don't we already do that when pruning HOT chains?
>
I thought that only happens after the transaction is committed, and
old enough, whereas the trigger code only needs to follow the chain in
the updating transaction.
Regards,
Dean