[MPICH] tricks for avioding locking problems

[Rajeev Thakur]

Which file system you use matters because different file systems have
different consistency semantics, and we accordingly have to compensate for
it in order to provide complete MPI-IO functionality. If you are using NFS,
you pretty much need locks to work unless you are only doing reads from the
file. On a true POSIX file system, you need locks to implement shared file
pointer, the atomic mode, and the data sieving optimization for
noncontiguous writes (which can be disabled with an info hint). We have come
up with a way to avoid locks on a POSIX file system by implementing the
equivalent of locks with MPI one-sided communication, and have 3 papers on
it, but it is not in the ROMIO release yet. (Locks will still be needed on
NFS to disable client-side caching.)
 
Rajeev
 


  _____  

From: owner-mpich-discuss at mcs.anl.gov
[mailto:owner-mpich-discuss at mcs.anl.gov] On Behalf Of Foucar, James G
Sent: Tuesday, June 21, 2005 4:34 PM
To: Rajeev Thakur; mpich-discuss at mcs.anl.gov
Subject: RE: [MPICH] tricks for avioding locking problems



Let's not focus on NFS at the moment. What I really need is a way, trick, or
hack that allows me to circumvent or disable file locking in general. Does
such a thing exist?

Thanks,
Jim


-----Original Message-----
From: Rajeev Thakur [mailto:thakur at mcs.anl.gov]
Sent: Tue 6/21/2005 3:25 PM
To: Foucar, James G; mpich-discuss at mcs.anl.gov
Subject: RE: [MPICH] tricks for avioding locking problems

One way to avoid this problem is to not use NFS :-).

Do you have the lockd daemon running on all nodes?

Rajeev


  _____ 

From: owner-mpich-discuss at mcs.anl.gov
[mailto:owner-mpich-discuss at mcs.anl.gov] On Behalf Of Foucar, James G
Sent: Tuesday, June 21, 2005 4:12 PM
To: mpich-discuss at mcs.anl.gov
Subject: [MPICH] tricks for avioding locking problems



Hello,

I was wondering if any of you know of ways to avoid the following error:

> File locking failed in ADIOI_Set_lock. If the file system is NFS, you
> need to use NFS version 3 and mount the directory with the 'noac' option
> (no attribute caching).
> [0] MPI Abort by user Aborting program !
> [0] Aborting program!
> p0_928:  p4_error: : 1
> exit 1

This error, and similar errors, have popped up randomly on all many file
systems, regardless of whether they were mounted with attribute caching.

I have tried using the MPI_MODE_UNIQUE_OPEN flag when opening files and some
other tricks, but nothing seems to get rid of this problem permanently on
all the various platforms that I need to support.

What I really need is a general way to tell MPICH not to use any file
locking or at least some way to avoid this error.

Thanks!
-Jim




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