Re: Proposed WAL changes

"Mikheev, Vadim" <vmikheev(at)SECTORBASE(dot)COM> writes:

> > > I feel that the fact that
> > >
> > > WAL can't help in the event of disk errors
> > >
> > > is often overlooked.
> >
> > This is true in general. But, nevertheless, WAL can be written to
> > protect against predictable disk errors, when possible. Failing to
> > write a couple of disk blocks when the system crashes is a reasonably
> > predictable disk error. WAL should ideally be written to work
> > correctly in that situation.
>
> But what can be done if fsync returns before pages flushed?

When you write out critical information, you keep earlier versions of
it. On startup, if the critical information is corrupt, you use the
earlier versions of it. This helps protect against the scenario I
mentioned: a few disk blocks may not have been written when the power
goes out.

My impression is that that is what Tom is doing with his patches.

Ian

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