[Users] meeting minutes for 2016-12-12

[Roland Haas]

Hello Frank, all,

> The garbled output, if not coming from two processes, look like a
> race. If it is, an explicit flush after output wouldn't solve the
> problem, but instead 'just' make it less likely to happen.
It only happens with 2 MPI ranks, yet I have checked that indeed only a
single rank writes data (or opens the file). This happens during a
single open/close cycle so it also is not related to opening/closing
the file.

> Yes. This smells like the filesystem or OS not invalidating a cache
> after a (probably cached) write to a file happened. The sysadmins
> should either know about it, or should be interested in it. If this
> is indeed the case, it should be possible to generate a simple test
> case show-casing the problem.
"Simple" is relative. The simplest reproducer I have is CarpetIOASCII's
newsep test which still fires up a lot of Cactus thorns (not really
required to just check that "-" is used instead of "::" for file
names). A simple test code that writes the same lines of data does not
show the problem (when run using MPI and 2 ranks of which only rank 0
actually writes).

Yours,
Roland

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