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dpiparo merged 2 commits into from
Oct 27, 2026
Merged

[skip-ci][NFC] update RNTuple related release notes #23858

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dee0262
[NFC] update release notes with SoA info
jblomer Oct 27, 2026
2c71477
[NFC] update release notes wrt RNTuple changes
jblomer Oct 27, 2026
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7 changes: 7 additions & 0 deletions README/ReleaseNotes/v642/index.md
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Expand Up @@ -153,6 +153,8 @@ Replace `obj.Connect(signal, "TPyDispatcher", disp, "Dispatch()")` with

* Reading a collection without its dictionary no longer crashes when the elements hold a `std::string` or a `TString`. The emulated collection proxy relocated its elements with a raw memory copy when its buffer had to grow, which corrupts an object that points into itself, such as a `std::string` using the small string optimization; the invalid pointer was then freed when the object was destroyed. Such elements are now destroyed and reconstructed at the new location instead. This affected for instance a `std::vector<std::pair<std::string,double>>` read back without a dictionary.

* An `RNTupleReader` will now by default not load all metadata on open. Metadata related to the on-disk location of data pages will instead be loaded during iteration. To restore the old behavior, set the metadata mode in the `RNTupleReadOptions` to `kEager`.

### RFile

RFile, ROOT's modern interface to ROOT file, has moved out of the `ROOT::Experimental` namespace.
Expand All @@ -170,6 +172,11 @@ Creating an RNTupleProcessor for joins can (for now) be done by calling `ROOT::E
* An experimental RDataFrame datasource using the RNTupleProcessor has been added.
RDataFrames can be created from an existing RNTupleProcessor by calling `ROOT::Experimental::RDF::FromRNTupleProcessor()`.

### RNTuple SoA I/O

The RNTuple SoA I/O classes moved out of experimental. These classes and the related dictionary options provide a mechanism to read and write a collection of a class, i.e. an "array of struct" (AoS),
as "struct of array" (SoA) in memory. This is useful, e.g., for efficient consumption of data structures by GPUs. This new feature comes with a technical documentation (`SoA.md`) and a tutorial (`ntpl020_SoA.C`).

## Core

* `TClass::IsTriviallyRelocatable()` reports whether an object of a class can be moved to a new address with a raw memory copy, i.e. without running a move or copy constructor (trivial relocatability in the C++26 sense). It is backed by the new `kClassIsTriviallyRelocatable` class property, which `TInterpreter::ClassInfo_ClassProperty()` now fills in. A class the interpreter does not know about, in particular an emulated one, is conservatively reported as not relocatable.
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