aod-merger: add option to skip non-existing files

[mario-krueger]

avoids crashes if the inputs.txt list for some reason contains files that dont exist or are not reachable

[jgrosseo]

Hi,
I am against this change. We can issue a fatal error in that case but we should not skip the file.
If the list cannot be processed an error has to be produced.

[mario-krueger]

Hi,
currently it will break with a seg fault and TFile::Open will issue an error message which probably is enough to see what is the problem. I can close the PR again if skipping the file is not what we want.
However, I was wondering if in production we would want one single corrupt file to break the whole merging chain. Maybe one could log the file names that did not work and print / save this somehow as a feedback to the operators instead?

[jgrosseo]

On the Grid, we do staged merging for analysis, so indeed you can have a failure on a certain level but this only involves a few files. The risk with skipping it that you never find those errors.

However, I see the use case in the merger for local use. So we could add that in case one passes a parameter --skip-not-existing that it goes to the next file as you suggested. What do you think?

[mario-krueger]

Hi,
sounds like a good compromise.
For the case where we want to abort the merging, the program now ends gracefully without a seg fault and propagates that there was an error to the caller, so merging scripts can react accordingly.

[jgrosseo]

Thanks! Here a few comments