Re: LMDB crash consistency, again

[Hallvard Breien Furuseth <h.b.furuseth@usit.uio.no>]

On 15/11/14 02:57, Howard Chu wrote:
> Ah good point. If you check out their slides, #103 of 106 asks the
> question; the only failure they found in LMDB occurred on ext3 (and not
> on XFS) so we may just chalk this up to a flaw in ext3 instead.
>
> Given that ext3 has already been superseded by ext4, this result of
> theirs may not be all that useful in the real world. We already have
> disrecommended ext3 for performance reasons, perhaps we should just note
> this and move on.


No, ext4 breaks too.  Their paper's page 459, 5.1.2 LightningDB:

    The fact that the journal commit block (op#402) is
    flushed with the next pwrite64 in the same thread
    means fdatasync on ext3 does not wait for the comple-
    tion of journaling (similar behavior has been observed
    on ext4).

I guess O_DSYNC and fdatasync() should not be the lmdb
defaults yet, at least not on Linux:-(

We need a bug report to Linux or to the distro they were
using, noting that the power faults are simulated.  And is
this O_DSYNC, fdatasync or both?  The problem might be with
only one of them.  I'm not reading the paper in detail yet.

--
Hallvard