Re: Disk IO - coss and ufs with common IO engines.

On Sun, Aug 31, 2003, Robert Collins wrote:

> > If you want to use the async io code rom anywhere, say, logfile writing,
> > you're _going_ to have to do write combining or your write queue is going
> > to quickly blow out to a stupid size. The store IO interface really assures
> > us there's only one outstanding write per object at a time, unless
> > something whacked has change which I haven't yet picked up on.
>
> This isn't the store IO interface. Each DiskFile can have multiple
> outstanding requests, both read or write. This is a requirement of COSS.

Ah, yes, of course it'll have to.

> Nope. That is a user-of-the-interface problem, it's not appropriate to
> force the interface to police this.
>
> We can certainly provide a write-combining Decorator though.
> Conceptually such a layer would:
> wrap the IOStrategy to return a decorated instance.
> wrap the DiskFile objects to intercept write's.
> Queue writes per File in memory, and when callback() is called, flush
> the queue to the real objects.
>
> Maybe 200 lines of code for the interested.

*nod* it'll still have to be done, else your write queues will start
filling and very quickly.

adrian
Received on Sun Aug 31 2003 - 17:17:21 MDT