I haven’t found consistent answer or me so I will ask the question again. For our analysis we make intermediate ntuples (flat TTree). Adding systematics can give ~2000 branches in a tree. We moved to this model from having one tree per systematic as this reduced the storage needed significantly.
But now I observe quite slow looping over the trees. Note that we merge ntuples to relatively large files (up to 90 GB) so that the amount of events per file is more consistent.
The questions are:
- Does the number of events in a tree matter? We can keep the individual file size smaller.
- How does the number of branches affect the performance? We do not load all branches at once when processing the file (only ~30 branches).
- Should we use non-default settings with handling such big amount of branches when creating the tree?
Thanks in advance for all answers (and sorry if some have already been answered before).
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