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[ntuple] Add slow merging strategy - #23739

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silverweed wants to merge 5 commits into
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silverweed:ntuple_merge_slow_4_2
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silverweed wants to merge 5 commits into
root-project:masterfrom
silverweed:ntuple_merge_slow_4_2

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@silverweed

@silverweed silverweed commented Oct 16, 2026 •

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This PR adds preliminary support for L4 ("slow") merging in the RNTupleMerger.
It does so by adding a new MergeStrategy that implements the slow merging flow. This is not yet enabled in any case by this PR but it will be used by attribute merging in a later PR.
I tested as much as I could this new flow and it works for most cases (the test failures that one would have by setting doSlowMerge = true are almost entirely due to test expectations that don't hold for slow merging).

Proper testing will be added when slow merging is enabled in the future, but for 6.42 it'll only be used by attributes, and they will get proper tests.

@silverweed
silverweed requested review from enirolf and hahnjo October 16, 2026 13:59
@silverweed silverweed self-assigned this Oct 16, 2026
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github-actions Bot commented Oct 16, 2026 •

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Test Results

    23 files      23 suites   3d 21h 25m 59s ⏱️
 3 889 tests  3 887 ✅ 0 💤 2 ❌
79 485 runs  79 483 ✅ 0 💤 2 ❌

For more details on these failures, see this check.

Results for commit 9e93a3c.

♻️ This comment has been updated with latest results.

@silverweed
silverweed force-pushed the ntuple_merge_slow_4_2 branch 3 times, most recently from 4060719 to 9e93a3c Compare October 20, 2026 14:21
Otherwise it'll gonna reuse the already-initialized source, which works
but it doesn't test the intended code path
For future use by the Merger
@silverweed
silverweed force-pushed the ntuple_merge_slow_4_2 branch 2 times, most recently from a1f9236 to 028c7c6 Compare October 23, 2026 08:40
@silverweed
silverweed requested a review from pcanal October 23, 2026 08:44
@silverweed
silverweed marked this pull request as ready for review October 23, 2026 08:44
@silverweed
silverweed requested a review from jblomer as a code owner October 23, 2026 08:44
@silverweed silverweed added this to the 6.42.00 milestone Oct 23, 2026
@silverweed
silverweed force-pushed the ntuple_merge_slow_4_2 branch from 028c7c6 to 75e930a Compare October 23, 2026 11:33
Comment thread tree/ntuple/inc/ROOT/RFieldBase.hxx Outdated
Comment thread tree/ntuple/src/RNTupleMerger.cxx Outdated
@silverweed
silverweed force-pushed the ntuple_merge_slow_4_2 branch from 75e930a to 486f2e0 Compare October 23, 2026 12:58
@silverweed
silverweed force-pushed the ntuple_merge_slow_4_2 branch from 486f2e0 to 8cfc0e7 Compare October 23, 2026 14:59

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2 participants