- Do we want a tool for users or devs, which can tell us the (I/O) performance of the setup (software + hardware)? (conclusion: we want a global ROOT I/O instrumentation)
- Do we want the tool to have many knobs or just a few? Everything configurable, not at all or sensible defaults? (rather less than more)
- We want a mechanic for RNtuple to get the reads in a file for sequential entries (2D plot of reads for location in file)
- Do we want a tool that gives recommendations to improve the throughput or just performance metrics?
- It seems like the dev questions to root-readspeed are different than the user questions. Do we want two different tools?
-> We want definitely a user focused tool, like root-readspeed, to answer for the analyst what blocks the analysis (decompression, network, ...)
- Do we want root-readspeed as standalone tool or an instrumentation of RDataFrame?
-> We want an instrumentation of ROOT, without touching the user code, to get such metrics!
- Conclusion (for now): We want a TTreePerfStats-like global instrumentation of the ROOT I/O, to be enabled in a debug mode.
- TTree: Should be possible without large-scale changes
- RNtuple: Only vaguely planned
- Favored solution would be an environment variable and a perf-like output file, which can be nicely visualized later.
- Still, root-readspeed is also a perfect tool to get the very best I/O throughput (e.g. just sequential reads)