rocksdb/db/compaction_iterator.h

//  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 <vector>

#include "db/compaction.h"
#include "db/compaction_iteration_stats.h"
#include "db/merge_helper.h"
#include "db/pinned_iterators_manager.h"
#include "db/range_del_aggregator.h"
#include "rocksdb/compaction_filter.h"

namespace rocksdb {

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();
    }

   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, Env* env,
                     bool expect_valid_internal_key,
                     RangeDelAggregator* range_del_agg,
                     const Compaction* compaction = nullptr,
                     const CompactionFilter* compaction_filter = nullptr,
                     const std::atomic<bool>* shutting_down = 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, Env* env,
                     bool expect_valid_internal_key,
                     RangeDelAggregator* range_del_agg,
                     std::unique_ptr<CompactionProxy> compaction,
                     const CompactionFilter* compaction_filter = nullptr,
                     const std::atomic<bool>* shutting_down = 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();

  // 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);

  InternalIterator* input_;
  const Comparator* cmp_;
  MergeHelper* merge_helper_;
  const std::vector<SequenceNumber>* snapshots_;
  const SequenceNumber earliest_write_conflict_snapshot_;
  Env* env_;
  bool expect_valid_internal_key_;
  RangeDelAggregator* range_del_agg_;
  std::unique_ptr<CompactionProxy> compaction_;
  const CompactionFilter* compaction_filter_;
  const std::atomic<bool>* shutting_down_;
  bool bottommost_level_;
  bool valid_ = false;
  bool visible_at_tip_;
  SequenceNumber earliest_snapshot_;
  SequenceNumber latest_snapshot_;
  bool ignore_snapshots_;

  // 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_;

  bool IsShuttingDown() {
    // This is a best-effort facility, so memory_order_relaxed is sufficient.
    return shutting_down_ && shutting_down_->load(std::memory_order_relaxed);
  }
};
}  // namespace rocksdb