Re: New Linux Filesystem: NILFS

On Tue, 2006-09-05 at 18:24 -0400, Chris Browne wrote:
> Recently seen in ACM Operating Systems Review (this is the first time
> I've found as many as 1 interesting article in it in a while, and
> there were 3 things I found worthwhile...):
>
> NTT (of the recent "NTT Power Hour") have created a new filesystem:
> <http://www.nilfs.org/en/>
>
> NILFS is a log-structured file system developed for Linux.
>

As I understand LFSs, they are not ideal for a database system. An LFS
is optimized so that it writes sequentially. However, PostgreSQL already
writes transactions sequentially in the WAL, and tries to optimize the
cleaning of dirty data pages with the background writer. So I don't see
the advantage of an LFS for a database.

Also, LFSs assume very effective read cache. Databases often hold much
more than can fit in read cache, and so frequently require disk access
for reads. An LFS scatters the data all over the disk, which destroys
the sequential access that PostgreSQL depends on for efficient index and
table scans.

Do you see an advantage in using LFS for PostgreSQL?

Did the quotation refer to people leaving write cache enabled on a
journaling filesystem?

Regards,
Jeff Davis