Re: [Postgres-xc-developers] [postgres-xc:bugs] #454 Update triggers on replicated tables may corrupt data

[Nikhil S. <ni...@st...>]

+1 for an approach using the Primary Key. As Pavan mentioned, maybe Update
already works using PK as an identifier so we might have a precedent
already.

Regards,
Nikhils


On Wed, Oct 9, 2013 at 12:12 PM, Pavan Deolasee <pav...@gm...>wrote:

> On Wed, Oct 9, 2013 at 12:09 PM, Andrei Martsinchyk <
> and...@gm...> wrote:
>
>> I believe even plain vacuum may move tuples within a page and purge empty
>> pages, therefore CTIDs could be changed.
>>
>
> Plain vacuum does not move tuples around.. Note that all indexes must be
> updated if a tuple is moved, even within a page. But besides that all your
> points below still hold true.
>
>
>> Autovacuum on Datamodes are not in sync and concurrent writes may occur
>> in different order on Datanodes.
>> CTID can not be used to identify tuple replicas. Primary key could be
>> used, or special system column. Otherwise not shippable updates against
>> replicated tables should not be allowed.
>>
>>
>> 2013/10/9 Pavan Deolasee <pav...@gm...>
>>
>>>
>>>
>>>
>>> On Wed, Oct 9, 2013 at 11:49 AM, Koichi Suzuki <koi...@gm...>wrote:
>>>
>>>> Hmm.. Yes, it could be serious.   I suppose that CTID changes only when
>>>> vacuum full occurs.
>>>>
>>>
>>> CTID will also change every time a row is updated. So the bug should be
>>> very easy to reproduce. One easiest way to compile different datanodes with
>>> diferent block size. Another way could be to update/delete from a
>>> replicated table and vacuum the table on one datanode but not other and
>>> then again update several rows in the table. Most likely the new versions
>>> on two different nodes will not have the same CTID anymore.
>>>
>>>
>>>> Vacuum freeze will updates xmim to the smallest value and usual vacuum
>>>> recycles "dead" row area.   We may have a chance to assign different CTIDs
>>>> to the same rows in replicated table if vacuum full runs locally in
>>>> datanodes.  (My assumption may be wrong.   Does vacuum freeze move tuples
>>>> and change their CTID?)
>>>>
>>>>
>>> No, it does not.
>>>
>>> Thanks,
>>> Pavan
>>>
>>> --
>>> Pavan Deolasee
>>> http://www.linkedin.com/in/pavandeolasee
>>>
>>>
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>>
>>
>> --
>> Andrei Martsinchyk
>>
>>
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>>
>
>
> --
> Pavan Deolasee
> http://www.linkedin.com/in/pavandeolasee
>
>
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