Xuan Baldauf writes:
> Hello Hans,
>
> are you considering pingpong-journaling for reiser4?
>
> Ping-Pong journaling is that, in the case you are able to
> know that the blocks you are writing to will be overwritten
> due to outstanding requests|future transactions, you do not
> write the invalidation block of the old transaction until
> the affected blocks are overwritten by the new transaction.
> Doing journaling in that way, you are bringing the count of
> required writes for journaling to the count of required
> writes for non-journaling (1 changed block, 1 write instead
> of 1 changed block, 1 write to the journal and 1 write to
> the real location), and thus saving half the
> journal-related writes in the ideal case. The superblock is
> a good candidate for this feature.
In reiserfs journalling written by Chris, transactions are "batched"
that is, sequence of transactions is accumulated in memory and then
dumped to journal area at once. If block was modified several times
during batch, it'll be written only once, so, in some sense, reiserfs
does have ping-pong journalling already.
>
> I think that heavily loaded servers with parallel disk
> writes will be able to see a considerable speedup.
>
> Xu�n.
Nikita.
