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distrdf backends test 2-3x slower since the cppyy migration, timing out on Ubuntu 26.10 #23675
Description
Since #21261 was merged on October 3, pyunittests-roottest-python-distrdf-backends-all takes two to three times longer in the ROOT Main nightlies, on all platforms in the table below. On Ubuntu 26.10 it hits the 1200 s timeout every night since October 5.
Test duration in seconds, in the last nightly before and the first nightly after the merge:
| Platform | Oct 3 | Oct 4 |
|---|---|---|
| alma10 | 173 | 370 |
| debian13 | 167 | 503 |
| fedora44 | 97 | 239 |
| mac26 ARM64 | 127 | 249 |
| ubuntu2604 | 185 | 427 |
| ubuntu2610 | 185 | 483 |
The durations were stable from September 29 to October 3 and stayed high from October 4 to October 9. The two nightlies were built from 47c95e1 and 3dbcdc4. Apart from #21261, the commits in between only change CI configuration, ntuple, version tag files and an error message in TSystem.
On ubuntu2604, the other Python tests did not get slower: the median ratio of their durations between the two nightlies is 0.89. So this seems specific to distributed RDataFrame.
On Ubuntu 26.10, pytest reports 279 passed in 568.68s and the process is then killed at 1200 s, so in addition the exit takes more than ten minutes there:
https://github.com/root-project/root/actions/runs/37870877150/job/113727903122
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guitargeek commentedon Oct 9, 2026
Thanks, this is a very important data point. Most of the issues and performance regressions with the cppjit migration were already on my radar and I have fixes in the pipeline. But my benchmark setup had the distrdf tests disabled so this slipped through the cracks.
@shuv-amp, so you plan to investigate this yourself or you want us to take over?
shuv-amp commentedon Oct 10, 2026
Thanks for taking it over, since you already have fixes in the pipeline.