> > ext3 dd 1303.84 66.87 212.49 66.06 361.04
> > dn 1288.03 64.62 209.27 111.41 278.54
> > bn 1285.32 65.98 1996.41 90.05 307.79
> This is ext3 with ordered data?
Yep. Everything is default unless otherwise stated.
> > minix dd 1305.26 67.38 207.74 193.90 228.81
> > dn 1331.27 67.14 210.07 223.70 214.33
> > bn 1299.24 89.58 1988.31 231.17 231.17
> Wow minix is faster than ext2 @) That certainly looks strange.
Yeah, I thought it was a little odd. Postgres does so much
fsync()ing that I thought it may just have been that the lower
overhead won out over ext2's cleverer layout. All the I/O was
basically fsync-driven, so this test was only about write
> Any chance to test XFS too?
Sure. I'll try to build a more interesting kernel sometime
this week. ext2 with delalloc might be fun, too.
Do you know of any simple patch or patches which might get
reiserfs working on 2.5.6?
> > 3. The journalled filesystems do have measurable overhead
> > for this workload.
> Normally (non data journaling, noatime) journaling fs shouldn't have
> any overhead for database load, because database files should be
> preallocated and the database should do direct IO in/out the
> preallocated buffers with the FS never doing any metadata writes,
> except for occassional inode updates for mtime depending on what sync
> mode that DB uses (hmm, I guess a nomtime or verylazymtime or
> alwaysasyncmtime mount option could be helpful for that)
Postgres doesn't pre-allocate datafiles. They reckon it's not
their job to implement a filesystem, and I'm inclined to agree.
They do prefer fdatasync on datafiles and (I think) O_DATASYNC
for their journal files where available, but I haven't checked
that my build is doing that.
> That's the theory, but doesn't seem to be the case in your test. I
> guess your test is not very realistic then.
Or your assumptions about DB vs filesystems are not valid in
> > 2. What does jfs do in the way of data journalling? Is it
> > "ordered" or "writeback", in ext3-speak? (I assume
> > fully journalled data would give much worse performance.)
> Kind of ordered I believe.
OK, ta. So it probably does something right that ext3
doesn't? (Or has rather weaker semantics, of course.)
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