Re: proposed: move FSFS protorevs out of the transactions dir

On Dec 25, 2007 6:01 PM, Branko Èibej <brane@xbc.nu> wrote:
> David Glasser wrote:
> > In already-bumped FSFS version 3, store the protorev and its lock
> > separately from the rest of the transaction metadata, to make it easy
> > for administrators to put the non-protorev metadata on a different
> > filesystem from the immutable filesystem.
> >
>
> Wouldn't doing that change an atomic rename to a non-atomic cross-device
> move?

Actually, avoiding that is the point :-)

It's already the case that the move-into-place code in FSFS checks for
a cross-device error, and does a copy instead in that case. Note,
though, that the "copy" is actually "copy to temporary file, then
atomically rename".

However, the point here is I want to make it possible to store the txn
metadata that *doesn't* get atomically moved on a different device,
and leave the proto-rev on the same device as the revs. The use case
I'm imagining would be to make db/transactions/ a symlink to local
disk, but leave db/txn-protorevs/ on the same device as db/revs/.

--dave

-- 
David Glasser | glasser_at_davidglasser.net | http://www.davidglasser.net/