[Lustre-discuss] Lustre, locking, and fsync

[Robert Olson]

Bah, of course there is a write of the new data to the file just  
before the fsync. The fd is also set for auto-flushing (this is a perl  
script).

On Feb 8, 2010, at 3:45 PM, Robert Olson wrote:

> I have a locking/fsync question..
>
> I have an app that keeps job metadata in an XML file that resides on  
> a Lustre filesystem (I actually just discovered my running system  
> has it on NFS, but I'm seeing an anomaly on Lustre so I'll keep  
> writing).
>
> It uses libxml to read and write the file, and thus has to read the  
> file into memory, make changes, and write back out.
>
> The approach I'm taking to this is:
>
> 	open file => fd
> 	lock fd (using fcntl F_SETLKW)
> 	read from fd
> 	ftruncate fd
> 	<make modifications>
> 	fsync fd
> 	unlock fd
> 	close fd
>
> The lustre system is a 4-OSS system and I'm running the test across  
> 12 compute nodes, all of which have the fs mounted with the flock  
> option (it falls over immediately without flock). I'm at lustre 1.6.6.
>
> What I'm seeing is that, occasionally, the file reads will pick up  
> an empty or partial file. This doesn't seem like it should be the  
> case, but I'm sure I'm missing something. I don't see any errors  
> showing up on the MDS.
>
> thanks,
> --bob
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