Re: unlogged tables

On Tue, Nov 16, 2010 at 7:46 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> On Tue, Nov 16, 2010 at 5:57 PM, marcin mank <marcin.mank@gmail.com> wrote:
>>> Can (should ?) unlogged tables' contents survive graceful (non-crash) shutdown?
>
>> I don't think so.  To make that work, you'd need to keep track of
>> every backing file that might contain pages not fsync()'d to disk, and
>> at shutdown time you'd need to fsync() them all before shutting down.
>
> This is presuming that we want to guarantee the same level of safety for
> unlogged tables as for regular.  Which, it seems to me, is exactly what
> people *aren't* asking for.  Why not just write the data and shut down?
> If you're unlucky enough to have a system crash immediately after that,
> well, you might have corrupt data in the unlogged tables ... but that
> doesn't seem real probable.

I have a hard time getting excited about a system that is designed to
ensure that we probably don't have data corruption.  The whole point
of this feature is to relax the usual data integrity guarantees in a
controlled way.  A small but uncertain risk of corruption is not an
improvement over a simple, predictable behavior.

--
Robert Haas
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