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 /// \file ROOT/RNTupleMerger.hxx
 /// \ingroup NTuple
 /// \author Jakob Blomer <jblomer@cern.ch>, Max Orok <maxwellorok@gmail.com>, Alaettin Serhan Mete <amete@anl.gov>
 /// \date 2020-07-08
 /// \warning This is part of the ROOT 7 prototype! It will change without notice. It might trigger earthquakes. Feedback
 /// is welcome!
 
 /*************************************************************************
  * Copyright (C) 1995-2020, Rene Brun and Fons Rademakers.               *
  * All rights reserved.                                                  *
  *                                                                       *
  * For the licensing terms see $ROOTSYS/LICENSE.                         *
  * For the list of contributors see $ROOTSYS/README/CREDITS.             *
  *************************************************************************/
 
 #ifndef ROOT_RNTupleMerger
 #define ROOT_RNTupleMerger
 
 #include <ROOT/RError.hxx>
 #include <ROOT/RNTupleDescriptor.hxx>
 #include <ROOT/RNTupleUtil.hxx>
 #include <ROOT/RPageStorage.hxx>
 #include <ROOT/TTaskGroup.hxx>
 #include <Compression.h>
 
 #include <memory>
 #include <optional>
 
 namespace ROOT {
 
 class RNTuple;
 
 namespace Internal {
 class RPageAllocator;
 class RClusterPool;
 }
 
 namespace Experimental::Internal {
 
 enum class ENTupleMergingMode {
    /// The merger will discard all columns that aren't present in the prototype model (i.e. the model of the first
    /// source); also all subsequent RNTuples must contain at least all the columns that are present in the prototype
    /// model
    kFilter,
    /// The merger will refuse to merge any 2 RNTuples whose schema doesn't match exactly
    kStrict,
    /// The merger will update the output model to include all columns from all sources. Entries corresponding to columns
    /// that are not present in a source will be set to the default value of the type.
    kUnion
 };
 
 enum class ENTupleMergeErrBehavior {
    /// The merger will abort merging as soon as an error is encountered
    kAbort,
    /// Upon errors, the merger will skip the current source and continue
    kSkip
 };
 
 struct RColumnMergeInfo;
 struct RNTupleMergeData;
 struct RSealedPageMergeData;
 
 /// Set of merging options to pass to RNTupleMerger.
 /// If you're using the merger through TFileMerger you need to give it string-based options instead.
 /// Here is the mapping for the TFileMerger options:
 ///   - "rntuple.MergingMode=(Filter|Union|...)" -> sets fMergingMode
 ///   - "rntuple.ErrBehavior=(Abort|Skip|...)"   -> sets fErrBehavior
 ///   - "rntuple.ExtraVerbose"                   -> sets fExtraVerbose to true
 /// Rules about the string-based options:
 ///   1. there must be no space between the separators (i.e. `.` and `=`)
 ///   2. all string matching is case insensitive
 struct RNTupleMergeOptions {
    /// If fCompressionSettings is empty (the default), the merger will not change the
    /// compression of any of its sources (fast merging). Otherwise, all sources will be converted to the specified
    /// compression algorithm and level.
    std::optional<std::uint32_t> fCompressionSettings;
    /// Determines how the merging treats sources with different models (\see ENTupleMergingMode).
    ENTupleMergingMode fMergingMode = ENTupleMergingMode::kFilter;
    /// Determines how the Merge function behaves upon merging errors
    ENTupleMergeErrBehavior fErrBehavior = ENTupleMergeErrBehavior::kAbort;
    /// If true, the merger will emit further diagnostics and information.
    bool fExtraVerbose = false;
 };
 
 // clang-format off
 /**
  * \class ROOT::Experimental::Internal::RNTupleMerger
  * \ingroup NTuple
  * \brief Given a set of RPageSources merge them into an RPagePersistentSink, optionally changing their compression.
  *        This can also be used to change the compression of a single RNTuple by just passing a single source.
  */
 // clang-format on
 class RNTupleMerger final {
    friend class ROOT::RNTuple;
 
    std::unique_ptr<ROOT::Internal::RPagePersistentSink> fDestination;
    std::unique_ptr<ROOT::Internal::RPageAllocator> fPageAlloc;
    std::optional<TTaskGroup> fTaskGroup;
    std::unique_ptr<ROOT::RNTupleModel> fModel;
 
    void MergeCommonColumns(ROOT::Internal::RClusterPool &clusterPool, const ROOT::RClusterDescriptor &clusterDesc,
                            std::span<const RColumnMergeInfo> commonColumns,
                            const ROOT::Internal::RCluster::ColumnSet_t &commonColumnSet,
                            std::size_t nCommonColumnsInCluster, RSealedPageMergeData &sealedPageData,
                            const RNTupleMergeData &mergeData, ROOT::Internal::RPageAllocator &pageAlloc);
 
    void MergeSourceClusters(ROOT::Internal::RPageSource &source, std::span<const RColumnMergeInfo> commonColumns,
                             std::span<const RColumnMergeInfo> extraDstColumns, RNTupleMergeData &mergeData);
 
    /// Creates a RNTupleMerger with the given destination.
    /// The model must be given if and only if `destination` has been initialized with that model
    /// (i.e. in case of incremental merging).
    RNTupleMerger(std::unique_ptr<ROOT::Internal::RPagePersistentSink> destination,
                  std::unique_ptr<ROOT::RNTupleModel> model);
 
 public:
    /// Creates a RNTupleMerger with the given destination.
    explicit RNTupleMerger(std::unique_ptr<ROOT::Internal::RPagePersistentSink> destination);
 
    /// Merge a given set of sources into the destination.
    /// Note that sources with an empty schema (i.e. created from a Model that had no fields added to it) are in
    /// general valid (depending on the merging mode) but add no entries to the destination.
    RResult<void> Merge(std::span<ROOT::Internal::RPageSource *> sources,
                        const RNTupleMergeOptions &mergeOpts = RNTupleMergeOptions());
 
 }; // end of class RNTupleMerger
 
 } // namespace Experimental::Internal
 } // namespace ROOT
 
 #endif

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