Re: LMDB crash consistency, again

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 Given that ext3 has already been superseded by ext4, this result of 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.