Re: Migrating from Informix to Postgre

Tommi Maekitalo <t.maekitalo@epgmbh.de> writes:

> >
> > > 4. Does it support raw devices?
> >
> > No.  We feel the performance improvement on raw devices is minimal.
> >
> But what about data-integrity? I've learned, that a write on a raw device
> guarantees, that the data is physically on the harddisk, when it returns.
> When you write into the filesystem you don't even have control about the
> order, in which writes are physically executed.
>
> It would be difficult to guarantee dataintegrity, when the datapages are
> written before WAL is on the hard-disk. That's why the Informix-people
> strongly suggests to use raw-devices.
>
> What does Postgresql do to guaratee it?

We call fsync() on the WAL files, which guarantees data is written
when it returns.

-Doug