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diff --git a/src/rocksdb/db/compaction/compaction_iterator.h b/src/rocksdb/db/compaction/compaction_iterator.h
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+++ b/src/rocksdb/db/compaction/compaction_iterator.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).
+#pragma once
+
+#include <algorithm>
+#include <deque>
+#include <string>
+#include <unordered_set>
+#include <vector>
+
+#include "db/compaction/compaction.h"
+#include "db/compaction/compaction_iteration_stats.h"
+#include "db/merge_helper.h"
+#include "db/pinned_iterators_manager.h"
+#include "db/range_del_aggregator.h"
+#include "db/snapshot_checker.h"
+#include "options/cf_options.h"
+#include "rocksdb/compaction_filter.h"
+
+namespace ROCKSDB_NAMESPACE {
+
+class CompactionIterator {
+ public:
+  // A wrapper around Compaction. Has a much smaller interface, only what
+  // CompactionIterator uses. Tests can override it.
+  class CompactionProxy {
+   public:
+    explicit CompactionProxy(const Compaction* compaction)
+        : compaction_(compaction) {}
+
+    virtual ~CompactionProxy() = default;
+    virtual int level(size_t /*compaction_input_level*/ = 0) const {
+      return compaction_->level();
+    }
+    virtual bool KeyNotExistsBeyondOutputLevel(
+        const Slice& user_key, std::vector<size_t>* level_ptrs) const {
+      return compaction_->KeyNotExistsBeyondOutputLevel(user_key, level_ptrs);
+    }
+    virtual bool bottommost_level() const {
+      return compaction_->bottommost_level();
+    }
+    virtual int number_levels() const { return compaction_->number_levels(); }
+    virtual Slice GetLargestUserKey() const {
+      return compaction_->GetLargestUserKey();
+    }
+    virtual bool allow_ingest_behind() const {
+      return compaction_->immutable_cf_options()->allow_ingest_behind;
+    }
+    virtual bool preserve_deletes() const {
+      return compaction_->immutable_cf_options()->preserve_deletes;
+    }
+
+   protected:
+    CompactionProxy() = default;
+
+   private:
+    const Compaction* compaction_;
+  };
+
+  CompactionIterator(
+      InternalIterator* input, const Comparator* cmp, MergeHelper* merge_helper,
+      SequenceNumber last_sequence, std::vector<SequenceNumber>* snapshots,
+      SequenceNumber earliest_write_conflict_snapshot,
+      const SnapshotChecker* snapshot_checker, Env* env,
+      bool report_detailed_time, bool expect_valid_internal_key,
+      CompactionRangeDelAggregator* range_del_agg,
+      const Compaction* compaction = nullptr,
+      const CompactionFilter* compaction_filter = nullptr,
+      const std::atomic<bool>* shutting_down = nullptr,
+      const SequenceNumber preserve_deletes_seqnum = 0,
+      const std::atomic<bool>* manual_compaction_paused = nullptr,
+      const std::shared_ptr<Logger> info_log = nullptr);
+
+  // Constructor with custom CompactionProxy, used for tests.
+  CompactionIterator(
+      InternalIterator* input, const Comparator* cmp, MergeHelper* merge_helper,
+      SequenceNumber last_sequence, std::vector<SequenceNumber>* snapshots,
+      SequenceNumber earliest_write_conflict_snapshot,
+      const SnapshotChecker* snapshot_checker, Env* env,
+      bool report_detailed_time, bool expect_valid_internal_key,
+      CompactionRangeDelAggregator* range_del_agg,
+      std::unique_ptr<CompactionProxy> compaction,
+      const CompactionFilter* compaction_filter = nullptr,
+      const std::atomic<bool>* shutting_down = nullptr,
+      const SequenceNumber preserve_deletes_seqnum = 0,
+      const std::atomic<bool>* manual_compaction_paused = nullptr,
+      const std::shared_ptr<Logger> info_log = nullptr);
+
+  ~CompactionIterator();
+
+  void ResetRecordCounts();
+
+  // Seek to the beginning of the compaction iterator output.
+  //
+  // REQUIRED: Call only once.
+  void SeekToFirst();
+
+  // Produces the next record in the compaction.
+  //
+  // REQUIRED: SeekToFirst() has been called.
+  void Next();
+
+  // Getters
+  const Slice& key() const { return key_; }
+  const Slice& value() const { return value_; }
+  const Status& status() const { return status_; }
+  const ParsedInternalKey& ikey() const { return ikey_; }
+  bool Valid() const { return valid_; }
+  const Slice& user_key() const { return current_user_key_; }
+  const CompactionIterationStats& iter_stats() const { return iter_stats_; }
+
+ private:
+  // Processes the input stream to find the next output
+  void NextFromInput();
+
+  // Do last preparations before presenting the output to the callee. At this
+  // point this only zeroes out the sequence number if possible for better
+  // compression.
+  void PrepareOutput();
+
+  // Invoke compaction filter if needed.
+  void InvokeFilterIfNeeded(bool* need_skip, Slice* skip_until);
+
+  // Given a sequence number, return the sequence number of the
+  // earliest snapshot that this sequence number is visible in.
+  // The snapshots themselves are arranged in ascending order of
+  // sequence numbers.
+  // Employ a sequential search because the total number of
+  // snapshots are typically small.
+  inline SequenceNumber findEarliestVisibleSnapshot(
+      SequenceNumber in, SequenceNumber* prev_snapshot);
+
+  // Checks whether the currently seen ikey_ is needed for
+  // incremental (differential) snapshot and hence can't be dropped
+  // or seqnum be zero-ed out even if all other conditions for it are met.
+  inline bool ikeyNotNeededForIncrementalSnapshot();
+
+  inline bool KeyCommitted(SequenceNumber sequence) {
+    return snapshot_checker_ == nullptr ||
+           snapshot_checker_->CheckInSnapshot(sequence, kMaxSequenceNumber) ==
+               SnapshotCheckerResult::kInSnapshot;
+  }
+
+  bool IsInEarliestSnapshot(SequenceNumber sequence);
+
+  InternalIterator* input_;
+  const Comparator* cmp_;
+  MergeHelper* merge_helper_;
+  const std::vector<SequenceNumber>* snapshots_;
+  // List of snapshots released during compaction.
+  // findEarliestVisibleSnapshot() find them out from return of
+  // snapshot_checker, and make sure they will not be returned as
+  // earliest visible snapshot of an older value.
+  // See WritePreparedTransactionTest::ReleaseSnapshotDuringCompaction3.
+  std::unordered_set<SequenceNumber> released_snapshots_;
+  std::vector<SequenceNumber>::const_iterator earliest_snapshot_iter_;
+  const SequenceNumber earliest_write_conflict_snapshot_;
+  const SnapshotChecker* const snapshot_checker_;
+  Env* env_;
+  bool report_detailed_time_;
+  bool expect_valid_internal_key_;
+  CompactionRangeDelAggregator* range_del_agg_;
+  std::unique_ptr<CompactionProxy> compaction_;
+  const CompactionFilter* compaction_filter_;
+  const std::atomic<bool>* shutting_down_;
+  const std::atomic<bool>* manual_compaction_paused_;
+  const SequenceNumber preserve_deletes_seqnum_;
+  bool bottommost_level_;
+  bool valid_ = false;
+  bool visible_at_tip_;
+  SequenceNumber earliest_snapshot_;
+  SequenceNumber latest_snapshot_;
+
+  // State
+  //
+  // Points to a copy of the current compaction iterator output (current_key_)
+  // if valid_.
+  Slice key_;
+  // Points to the value in the underlying iterator that corresponds to the
+  // current output.
+  Slice value_;
+  // The status is OK unless compaction iterator encounters a merge operand
+  // while not having a merge operator defined.
+  Status status_;
+  // Stores the user key, sequence number and type of the current compaction
+  // iterator output (or current key in the underlying iterator during
+  // NextFromInput()).
+  ParsedInternalKey ikey_;
+  // Stores whether ikey_.user_key is valid. If set to false, the user key is
+  // not compared against the current key in the underlying iterator.
+  bool has_current_user_key_ = false;
+  bool at_next_ = false;  // If false, the iterator
+  // Holds a copy of the current compaction iterator output (or current key in
+  // the underlying iterator during NextFromInput()).
+  IterKey current_key_;
+  Slice current_user_key_;
+  SequenceNumber current_user_key_sequence_;
+  SequenceNumber current_user_key_snapshot_;
+
+  // True if the iterator has already returned a record for the current key.
+  bool has_outputted_key_ = false;
+
+  // truncated the value of the next key and output it without applying any
+  // compaction rules.  This is used for outputting a put after a single delete.
+  bool clear_and_output_next_key_ = false;
+
+  MergeOutputIterator merge_out_iter_;
+  // PinnedIteratorsManager used to pin input_ Iterator blocks while reading
+  // merge operands and then releasing them after consuming them.
+  PinnedIteratorsManager pinned_iters_mgr_;
+  std::string compaction_filter_value_;
+  InternalKey compaction_filter_skip_until_;
+  // "level_ptrs" holds indices that remember which file of an associated
+  // level we were last checking during the last call to compaction->
+  // KeyNotExistsBeyondOutputLevel(). This allows future calls to the function
+  // to pick off where it left off since each subcompaction's key range is
+  // increasing so a later call to the function must be looking for a key that
+  // is in or beyond the last file checked during the previous call
+  std::vector<size_t> level_ptrs_;
+  CompactionIterationStats iter_stats_;
+
+  // Used to avoid purging uncommitted values. The application can specify
+  // uncommitted values by providing a SnapshotChecker object.
+  bool current_key_committed_;
+  std::shared_ptr<Logger> info_log_;
+
+  bool IsShuttingDown() {
+    // This is a best-effort facility, so memory_order_relaxed is sufficient.
+    return shutting_down_ && shutting_down_->load(std::memory_order_relaxed);
+  }
+
+  bool IsPausingManualCompaction() {
+    // This is a best-effort facility, so memory_order_relaxed is sufficient.
+    return manual_compaction_paused_ &&
+           manual_compaction_paused_->load(std::memory_order_relaxed);
+  }
+};
+}  // namespace ROCKSDB_NAMESPACE