Re: unlogged tables

On 14 November 2011 14:17, Richard Huxton <dev(at)archonet(dot)com> wrote:
> On 14/11/11 10:08, Sergey Konoplev wrote:
>>
>> On 14 November 2011 12:58, Richard Huxton<dev(at)archonet(dot)com>  wrote:
> Let's say you were doing something like "UPDATE unlogged_table SET x=1 WHERE
> y=2". If a crash occurs during this command, there's no guarantee that the
> affected disk pages were all updated. Worse, a single page might be
> partially updated or even have rubbish in it (depending on the nature of the
> crash).
>
> Without the WAL there's no way to check whether the table is good or not, or
> even to know what the last updates were. So - the only safe thing to do is
> truncate the unlogged tables.
>
> In the event of a normal shutdown, we can flush all the writes to disk so we
> know all the data has been written, so there is no need to truncate.

Thank you for the explanation. Now I understand it.

>
> --
>  Richard Huxton
>  Archonet Ltd
>

--
Sergey Konoplev

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