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diff --git a/src/rocksdb/db/compaction/compaction.h b/src/rocksdb/db/compaction/compaction.h
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+//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under both the GPLv2 (found in the
+//  COPYING file in the root directory) and Apache 2.0 License
+//  (found in the LICENSE.Apache file in the root directory).
+//
+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+
+#pragma once
+#include "db/version_set.h"
+#include "memory/arena.h"
+#include "options/cf_options.h"
+#include "util/autovector.h"
+
+namespace ROCKSDB_NAMESPACE {
+// The file contains class Compaction, as well as some helper functions
+// and data structures used by the class.
+
+// Utility for comparing sstable boundary keys. Returns -1 if either a or b is
+// null which provides the property that a==null indicates a key that is less
+// than any key and b==null indicates a key that is greater than any key. Note
+// that the comparison is performed primarily on the user-key portion of the
+// key. If the user-keys compare equal, an additional test is made to sort
+// range tombstone sentinel keys before other keys with the same user-key. The
+// result is that 2 user-keys will compare equal if they differ purely on
+// their sequence number and value, but the range tombstone sentinel for that
+// user-key will compare not equal. This is necessary because the range
+// tombstone sentinel key is set as the largest key for an sstable even though
+// that key never appears in the database. We don't want adjacent sstables to
+// be considered overlapping if they are separated by the range tombstone
+// sentinel.
+int sstableKeyCompare(const Comparator* user_cmp, const InternalKey& a,
+                      const InternalKey& b);
+int sstableKeyCompare(const Comparator* user_cmp, const InternalKey* a,
+                      const InternalKey& b);
+int sstableKeyCompare(const Comparator* user_cmp, const InternalKey& a,
+                      const InternalKey* b);
+
+// An AtomicCompactionUnitBoundary represents a range of keys [smallest,
+// largest] that exactly spans one ore more neighbouring SSTs on the same
+// level. Every pair of  SSTs in this range "overlap" (i.e., the largest
+// user key of one file is the smallest user key of the next file). These
+// boundaries are propagated down to RangeDelAggregator during compaction
+// to provide safe truncation boundaries for range tombstones.
+struct AtomicCompactionUnitBoundary {
+  const InternalKey* smallest = nullptr;
+  const InternalKey* largest = nullptr;
+};
+
+// The structure that manages compaction input files associated
+// with the same physical level.
+struct CompactionInputFiles {
+  int level;
+  std::vector<FileMetaData*> files;
+  std::vector<AtomicCompactionUnitBoundary> atomic_compaction_unit_boundaries;
+  inline bool empty() const { return files.empty(); }
+  inline size_t size() const { return files.size(); }
+  inline void clear() { files.clear(); }
+  inline FileMetaData* operator[](size_t i) const { return files[i]; }
+};
+
+class Version;
+class ColumnFamilyData;
+class VersionStorageInfo;
+class CompactionFilter;
+
+// A Compaction encapsulates metadata about a compaction.
+class Compaction {
+ public:
+  Compaction(VersionStorageInfo* input_version,
+             const ImmutableCFOptions& immutable_cf_options,
+             const MutableCFOptions& mutable_cf_options,
+             std::vector<CompactionInputFiles> inputs, int output_level,
+             uint64_t target_file_size, uint64_t max_compaction_bytes,
+             uint32_t output_path_id, CompressionType compression,
+             CompressionOptions compression_opts, uint32_t max_subcompactions,
+             std::vector<FileMetaData*> grandparents,
+             bool manual_compaction = false, double score = -1,
+             bool deletion_compaction = false,
+             CompactionReason compaction_reason = CompactionReason::kUnknown);
+
+  // No copying allowed
+  Compaction(const Compaction&) = delete;
+  void operator=(const Compaction&) = delete;
+
+  ~Compaction();
+
+  // Returns the level associated to the specified compaction input level.
+  // If compaction_input_level is not specified, then input_level is set to 0.
+  int level(size_t compaction_input_level = 0) const {
+    return inputs_[compaction_input_level].level;
+  }
+
+  int start_level() const { return start_level_; }
+
+  // Outputs will go to this level
+  int output_level() const { return output_level_; }
+
+  // Returns the number of input levels in this compaction.
+  size_t num_input_levels() const { return inputs_.size(); }
+
+  // Return the object that holds the edits to the descriptor done
+  // by this compaction.
+  VersionEdit* edit() { return &edit_; }
+
+  // Returns the number of input files associated to the specified
+  // compaction input level.
+  // The function will return 0 if when "compaction_input_level" < 0
+  // or "compaction_input_level" >= "num_input_levels()".
+  size_t num_input_files(size_t compaction_input_level) const {
+    if (compaction_input_level < inputs_.size()) {
+      return inputs_[compaction_input_level].size();
+    }
+    return 0;
+  }
+
+  // Returns input version of the compaction
+  Version* input_version() const { return input_version_; }
+
+  // Returns the ColumnFamilyData associated with the compaction.
+  ColumnFamilyData* column_family_data() const { return cfd_; }
+
+  // Returns the file meta data of the 'i'th input file at the
+  // specified compaction input level.
+  // REQUIREMENT: "compaction_input_level" must be >= 0 and
+  //              < "input_levels()"
+  FileMetaData* input(size_t compaction_input_level, size_t i) const {
+    assert(compaction_input_level < inputs_.size());
+    return inputs_[compaction_input_level][i];
+  }
+
+  const std::vector<AtomicCompactionUnitBoundary>* boundaries(
+      size_t compaction_input_level) const {
+    assert(compaction_input_level < inputs_.size());
+    return &inputs_[compaction_input_level].atomic_compaction_unit_boundaries;
+  }
+
+  // Returns the list of file meta data of the specified compaction
+  // input level.
+  // REQUIREMENT: "compaction_input_level" must be >= 0 and
+  //              < "input_levels()"
+  const std::vector<FileMetaData*>* inputs(
+      size_t compaction_input_level) const {
+    assert(compaction_input_level < inputs_.size());
+    return &inputs_[compaction_input_level].files;
+  }
+
+  const std::vector<CompactionInputFiles>* inputs() { return &inputs_; }
+
+  // Returns the LevelFilesBrief of the specified compaction input level.
+  const LevelFilesBrief* input_levels(size_t compaction_input_level) const {
+    return &input_levels_[compaction_input_level];
+  }
+
+  // Maximum size of files to build during this compaction.
+  uint64_t max_output_file_size() const { return max_output_file_size_; }
+
+  // What compression for output
+  CompressionType output_compression() const { return output_compression_; }
+
+  // What compression options for output
+  CompressionOptions output_compression_opts() const {
+    return output_compression_opts_;
+  }
+
+  // Whether need to write output file to second DB path.
+  uint32_t output_path_id() const { return output_path_id_; }
+
+  // Is this a trivial compaction that can be implemented by just
+  // moving a single input file to the next level (no merging or splitting)
+  bool IsTrivialMove() const;
+
+  // If true, then the compaction can be done by simply deleting input files.
+  bool deletion_compaction() const { return deletion_compaction_; }
+
+  // Add all inputs to this compaction as delete operations to *edit.
+  void AddInputDeletions(VersionEdit* edit);
+
+  // Returns true if the available information we have guarantees that
+  // the input "user_key" does not exist in any level beyond "output_level()".
+  bool KeyNotExistsBeyondOutputLevel(const Slice& user_key,
+                                     std::vector<size_t>* level_ptrs) const;
+
+  // Clear all files to indicate that they are not being compacted
+  // Delete this compaction from the list of running compactions.
+  //
+  // Requirement: DB mutex held
+  void ReleaseCompactionFiles(Status status);
+
+  // Returns the summary of the compaction in "output" with maximum "len"
+  // in bytes.  The caller is responsible for the memory management of
+  // "output".
+  void Summary(char* output, int len);
+
+  // Return the score that was used to pick this compaction run.
+  double score() const { return score_; }
+
+  // Is this compaction creating a file in the bottom most level?
+  bool bottommost_level() const { return bottommost_level_; }
+
+  // Does this compaction include all sst files?
+  bool is_full_compaction() const { return is_full_compaction_; }
+
+  // Was this compaction triggered manually by the client?
+  bool is_manual_compaction() const { return is_manual_compaction_; }
+
+  // Used when allow_trivial_move option is set in
+  // Universal compaction. If all the input files are
+  // non overlapping, then is_trivial_move_ variable
+  // will be set true, else false
+  void set_is_trivial_move(bool trivial_move) {
+    is_trivial_move_ = trivial_move;
+  }
+
+  // Used when allow_trivial_move option is set in
+  // Universal compaction. Returns true, if the input files
+  // are non-overlapping and can be trivially moved.
+  bool is_trivial_move() const { return is_trivial_move_; }
+
+  // How many total levels are there?
+  int number_levels() const { return number_levels_; }
+
+  // Return the ImmutableCFOptions that should be used throughout the compaction
+  // procedure
+  const ImmutableCFOptions* immutable_cf_options() const {
+    return &immutable_cf_options_;
+  }
+
+  // Return the MutableCFOptions that should be used throughout the compaction
+  // procedure
+  const MutableCFOptions* mutable_cf_options() const {
+    return &mutable_cf_options_;
+  }
+
+  // Returns the size in bytes that the output file should be preallocated to.
+  // In level compaction, that is max_file_size_. In universal compaction, that
+  // is the sum of all input file sizes.
+  uint64_t OutputFilePreallocationSize() const;
+
+  void SetInputVersion(Version* input_version);
+
+  struct InputLevelSummaryBuffer {
+    char buffer[128];
+  };
+
+  const char* InputLevelSummary(InputLevelSummaryBuffer* scratch) const;
+
+  uint64_t CalculateTotalInputSize() const;
+
+  // In case of compaction error, reset the nextIndex that is used
+  // to pick up the next file to be compacted from files_by_size_
+  void ResetNextCompactionIndex();
+
+  // Create a CompactionFilter from compaction_filter_factory
+  std::unique_ptr<CompactionFilter> CreateCompactionFilter() const;
+
+  // Is the input level corresponding to output_level_ empty?
+  bool IsOutputLevelEmpty() const;
+
+  // Should this compaction be broken up into smaller ones run in parallel?
+  bool ShouldFormSubcompactions() const;
+
+  // test function to validate the functionality of IsBottommostLevel()
+  // function -- determines if compaction with inputs and storage is bottommost
+  static bool TEST_IsBottommostLevel(
+      int output_level, VersionStorageInfo* vstorage,
+      const std::vector<CompactionInputFiles>& inputs);
+
+  TablePropertiesCollection GetOutputTableProperties() const {
+    return output_table_properties_;
+  }
+
+  void SetOutputTableProperties(TablePropertiesCollection tp) {
+    output_table_properties_ = std::move(tp);
+  }
+
+  Slice GetSmallestUserKey() const { return smallest_user_key_; }
+
+  Slice GetLargestUserKey() const { return largest_user_key_; }
+
+  int GetInputBaseLevel() const;
+
+  CompactionReason compaction_reason() { return compaction_reason_; }
+
+  const std::vector<FileMetaData*>& grandparents() const {
+    return grandparents_;
+  }
+
+  uint64_t max_compaction_bytes() const { return max_compaction_bytes_; }
+
+  uint32_t max_subcompactions() const { return max_subcompactions_; }
+
+  uint64_t MinInputFileOldestAncesterTime() const;
+
+ private:
+  // mark (or clear) all files that are being compacted
+  void MarkFilesBeingCompacted(bool mark_as_compacted);
+
+  // get the smallest and largest key present in files to be compacted
+  static void GetBoundaryKeys(VersionStorageInfo* vstorage,
+                              const std::vector<CompactionInputFiles>& inputs,
+                              Slice* smallest_key, Slice* largest_key);
+
+  // Get the atomic file boundaries for all files in the compaction. Necessary
+  // in order to avoid the scenario described in
+  // https://github.com/facebook/rocksdb/pull/4432#discussion_r221072219 and plumb
+  // down appropriate key boundaries to RangeDelAggregator during compaction.
+  static std::vector<CompactionInputFiles> PopulateWithAtomicBoundaries(
+      VersionStorageInfo* vstorage, std::vector<CompactionInputFiles> inputs);
+
+  // helper function to determine if compaction with inputs and storage is
+  // bottommost
+  static bool IsBottommostLevel(
+      int output_level, VersionStorageInfo* vstorage,
+      const std::vector<CompactionInputFiles>& inputs);
+
+  static bool IsFullCompaction(VersionStorageInfo* vstorage,
+                               const std::vector<CompactionInputFiles>& inputs);
+
+  VersionStorageInfo* input_vstorage_;
+
+  const int start_level_;    // the lowest level to be compacted
+  const int output_level_;  // levels to which output files are stored
+  uint64_t max_output_file_size_;
+  uint64_t max_compaction_bytes_;
+  uint32_t max_subcompactions_;
+  const ImmutableCFOptions immutable_cf_options_;
+  const MutableCFOptions mutable_cf_options_;
+  Version* input_version_;
+  VersionEdit edit_;
+  const int number_levels_;
+  ColumnFamilyData* cfd_;
+  Arena arena_;          // Arena used to allocate space for file_levels_
+
+  const uint32_t output_path_id_;
+  CompressionType output_compression_;
+  CompressionOptions output_compression_opts_;
+  // If true, then the comaction can be done by simply deleting input files.
+  const bool deletion_compaction_;
+
+  // Compaction input files organized by level. Constant after construction
+  const std::vector<CompactionInputFiles> inputs_;
+
+  // A copy of inputs_, organized more closely in memory
+  autovector<LevelFilesBrief, 2> input_levels_;
+
+  // State used to check for number of overlapping grandparent files
+  // (grandparent == "output_level_ + 1")
+  std::vector<FileMetaData*> grandparents_;
+  const double score_;         // score that was used to pick this compaction.
+
+  // Is this compaction creating a file in the bottom most level?
+  const bool bottommost_level_;
+  // Does this compaction include all sst files?
+  const bool is_full_compaction_;
+
+  // Is this compaction requested by the client?
+  const bool is_manual_compaction_;
+
+  // True if we can do trivial move in Universal multi level
+  // compaction
+  bool is_trivial_move_;
+
+  // Does input compression match the output compression?
+  bool InputCompressionMatchesOutput() const;
+
+  // table properties of output files
+  TablePropertiesCollection output_table_properties_;
+
+  // smallest user keys in compaction
+  Slice smallest_user_key_;
+
+  // largest user keys in compaction
+  Slice largest_user_key_;
+
+  // Reason for compaction
+  CompactionReason compaction_reason_;
+};
+
+// Return sum of sizes of all files in `files`.
+extern uint64_t TotalFileSize(const std::vector<FileMetaData*>& files);
+
+}  // namespace ROCKSDB_NAMESPACE