Bug #1777
Teach mdrun about explicit -append
Description
In all cases below, I run
gmx mdrun -deffnm first -nsteps 100 gmx convert-tpr -s first -extend 1 -o second
as the sole preparation for mdrun in an empty directory (but I repeat those commands for clarity):
1)
gmx mdrun -deffnm first -nsteps 100 gmx convert-tpr -s first -extend 1 -o second gmx mdrun -s second -deffnm second
writes second.* output files starting from step 0, which is fine
2)
gmx mdrun -deffnm first -nsteps 100 gmx convert-tpr -s first -extend 1 -o second gmx mdrun -s second -deffnm second -append
does the same as 1), which is not necessarily fine. Presumably this is because -append is the default and we haven't taught mdrun how to know that the user explicitly asked for appending. mdrun can't tell whether the use of -deffnm or -append (or missing files) is the error, so we should kick that decision back to the user.
3)
gmx mdrun -deffnm first -nsteps 100 gmx convert-tpr -s first -extend 1 -o second gmx mdrun -s second -deffnm second -cpi first
writes second.* output files, starting from step 100, which is fine
4)
gmx mdrun -deffnm first -nsteps 100 gmx convert-tpr -s first -extend 1 -o second gmx mdrun -s second -deffnm second -cpi first -append
does the same as 3), which is not necessarily fine. Similarly, mdrun can't tell whether the use of
-deffnm, -cpi or -append (or missing files) is the error, so we should kick that decision back to the user.
5)
gmx mdrun -deffnm first -nsteps 100 gmx convert-tpr -s first -extend 1 -o second gmx mdrun -s second -append
writes output files with default names, starting from step 0, again not fine because mdrun doesn't know where the error happened
6)
gmx mdrun -deffnm first -nsteps 100 gmx convert-tpr -s first -extend 1 -o second gmx mdrun -s second -cpi first -append
writes output files with default names, starting from step 100, again not fine because mdrun doesn't know where the error happened
At https://mailman-1.sys.kth.se/pipermail/gromacs.org_gmx-users/2015-July/099153.html, a new user tried to do 6), and expected the output to be appended to first.*.
7)
gmx mdrun -deffnm first -nsteps 100 gmx convert-tpr -s first -extend 1 -o second gmx mdrun -s second -deffnm second -cpi first -nsteps 100 gmx mdrun -s second -deffnm second -cpi second -append
starts from step 200 and appends to the existing second.* files, which is fine
8)
gmx mdrun -deffnm first -nsteps 100 gmx convert-tpr -s first -extend 1 -o second gmx mdrun -s second -deffnm second -cpi first -nsteps 100 gmx mdrun -s second -deffnm second -append
starts from step 0 and replaces the existing second.* files, but should give an error. That error should be different depending whether second.cpt exists
9)
gmx mdrun -deffnm first -nsteps 100 gmx convert-tpr -s first -extend 1 -o second gmx mdrun -s second -deffnm second -cpi first -nsteps 100 gmx mdrun -s second -deffnm second -cpi first -append
starts from step 100 and replaces the existing second.* files, but should give an error
10)
gmx mdrun -deffnm first -nsteps 100 gmx convert-tpr -s first -extend 1 -o second gmx mdrun -s second -deffnm second -cpi first -nsteps 100 gmx mdrun -s second -deffnm second -cpi second -nsteps 100 gmx mdrun -s second -deffnm second -cpi first -append
starts from step 100 and replaces the existing second.* files, but should give an error
https://gerrit.gromacs.org/#/c/4439/ is related, but IIRC doesn't fix any of this
Related issues
Associated revisions
History
#1 Updated by Mark Abraham about 5 years ago
Some ambiguity here is resolved if we remove the ability for the user to give arbitrary names to mdrun output files. -deffnm is useful and has been around for a while, but is not a great name if that's the only functionality available. I would like something like gmx mdrun -name, perhaps with -deffnm also supported for backward compatibility. Similarly, I think we should drop -multi in favour of -multidir, not least because I expect that the latter is easier to implement and test in combination with gmx mdrun -name
#2 Updated by Erik Lindahl over 4 years ago
I would strongly recommend that we do NOT allow appending in any other case than continuing from a checkpoint.
There is a history of stupid errors just because we have had umpteen different ways to continue a run, which leads to way too many combinations to test... and then there are bugs.
So, in short: The -append flag is only meant to continue from checkpoint, not a convenience flag to concatenate completed trajectories on-the-fly.
The reason we originally added it was originally that we wanted to play it safe, and we might still want it for the extreme corner case of file systems that don't support appending, but nothing else.
#3 Updated by Erik Lindahl about 4 years ago
- Status changed from New to Accepted
Based on discussions with Mark last Friday, we both decided it's better to limit append to checkpoint continuation, as it was originally designed for. By default it is always on, but we do allow users to force separate files instead.
However, it was never meant as a convenience replacement for being able to concatenate any independent trajectories already at runtime, and should not be used as such.
#4 Updated by Mark Abraham about 4 years ago
Agreed. That decision might break some existing workflows, but we should apologise for past errors and focus on building tools that work provably well for the important mainstream cases.
#5 Updated by Mark Abraham about 4 years ago
- Related to Bug #1889: mdrun -cpi file presence dilemma added
#6 Updated by Erik Lindahl about 4 years ago
Issuing a fatal error when -append is used without checkpointing is easy, but not sufficient.
It seems like most of these cases are caused by using convert-tpr to alter runs, and/or the -nsteps option to mdrun. The whole idea of arbitrarily altering input files, renaming them, and overriding settings on the command line - but still being able to continue the same trajectory - opens a horrible can of worms that is quite clearly WAY too complex to handle correctly.
I would vote for
1) Removing the -extend option to convert-tpr, and limit it to a tool used for altering tpr files for analysis.
2) Replacing the -nsteps option with a -maxsteps option. We will NOT write more data than what was requested in the input, but it is possible to stop earlier.
When a user want a particular number of steps we have a clearly prescribed way to achieve that: The "nsteps" option in the mdp file. Let's stick to that and avoid screwing things up.
#7 Updated by Erik Lindahl about 4 years ago
Here's a proposed solution for the more immediate problem - in combination these should solve all the issues listed:
1) Refuse an explicit -append without checkpoint.
2) Refuse to run when we cannot the files to append to (unless -noappend was used)
3) Store the names of the original files in the checkpoint, and refuse to append to anything else.
#8 Updated by Gerrit Code Review Bot about 4 years ago
Gerrit received a related patchset '1' for Issue #1777.
Uploader: Erik Lindahl (erik.lindahl@gmail.com)
Change-Id: Id9e89773a4a9214be6dbb76676c526e98e12bd37
Gerrit URL: https://gerrit.gromacs.org/5890
#9 Updated by Erik Lindahl about 4 years ago
- Status changed from Accepted to Fix uploaded
#10 Updated by Erik Lindahl about 4 years ago
- Status changed from Fix uploaded to Resolved
Applied in changeset 07d120957728dd271752128113b58b45f6b8e194.
#11 Updated by Mark Abraham about 4 years ago
- Target version changed from future to 2016
#12 Updated by Mark Abraham about 4 years ago
- Status changed from Resolved to Closed
#13 Updated by Mark Abraham over 3 years ago
- Related to Task #1781: re-design benchmarking functionality added
#14 Updated by Mark Abraham over 3 years ago
- Related to Task #2169: remove 'continuation' mdp option added
Prevent fragile use cases of checkpoint appending
There are way too many ways we allow runs to be continued
and extended. We still allow the checkpoint file to be
missing (so -cpi can be used for all command lines), but
we warn if it is not found. To avoid mistakes with file
appending when restarting from checkpoints, we now require
that all previous output files must be present
(unless -noappend is used), and that the file names must
match the ones used in the previous run.
Fixes #1777.
Change-Id: Id9e89773a4a9214be6dbb76676c526e98e12bd37