56C represents an additional significant improvement in performance,
plus bug fixes and most of the final media changes.
As with all the commits this week, a kernel and utilities rebuild plus
a newfs_hammer is needed to continue testing.
The filesystem block size now increases from 16K to 64K once a file
has grown past 1MB. This improves write performance to the point
where I don't really need to implement cluster_write(), so I've decided
to forego doing that for the release.
I will be making one final media change on Friday and then HAMMER
development will go into testing & bug fixing mode until the release.
This last media change will fix mtime and atime storage. At the moment
mtime/atime updates require generating UNDO records and, needless to say,
they're expensive. I will consider my options tomorrow but I think I
am going to just not include those fields in the CRC so they can be
updated asynchronously, without any UNDO's.
I have really begun pounding the filesystem by running blogbench,
buildworld -j 8, and fsx simultaniously on two test boxes. I expect
that any remaining bugs will be worked out over the next week or two.
All performance work except for the atime/mtime issue is now complete.
WYSIWYG. HAMMER's performance is extremely good now, and its system
cpu overhead has dropped to roughly the same that we get from UFS
(buildworlds run 610-620 seconds of system time for HAMMER, and
610-620 seconds of system time for UFS).
HAMMER is now able to sustain full disk bandwidth for bulk reads and
writes. HAMMER continues to have far superior random-write performance,
whether the system caches are blown out or not. Not only that but
the performance can potentially improve even more if I redo the
deadlock avoidance algorithms. HAMMER is within 10% of UFS's read
That's harmless for atime, but you really want mtime to be properly
synchronised with the last data update (and to stay that way across an
undo). Ideally, timestamp data records and hold mtime as a reference
to the last one updated (or something like that).
Bob Bishop +44 (0)118 940 1243
email@example.com fax +44 (0)118 940 1295