rocksdb/db/read_callback.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 "rocksdb/types.h"

namespace rocksdb {

class ReadCallback {
 public:
  ReadCallback() {}
  ReadCallback(SequenceNumber snapshot) : snapshot_(snapshot) {}
  ReadCallback(SequenceNumber snapshot, SequenceNumber min_uncommitted)
      : snapshot_(snapshot), min_uncommitted_(min_uncommitted) {}

  virtual ~ReadCallback() {}

  // Will be called to see if the seq number visible; if not it moves on to
  // the next seq number.
  virtual bool IsVisibleFullCheck(SequenceNumber seq) = 0;

  inline bool IsVisible(SequenceNumber seq) {
    if (seq == 0 || seq < min_uncommitted_) {
      assert(seq <= snapshot_);
      return true;
    } else if (snapshot_ < seq) {
      return false;
    } else {
      return IsVisibleFullCheck(seq);
    }
  }

  // This is called to determine the maximum visible sequence number for the
  // current transaction for read-your-own-write semantics. This is so that
  // for write unprepared, we will not skip keys that are written by the
  // current transaction with the seek to snapshot optimization.
  //
  // For other uses, this returns zero, meaning that the current snapshot
  // sequence number is the maximum visible sequence number.
  inline virtual SequenceNumber MaxUnpreparedSequenceNumber() { return 0; };

 protected:
  // The snapshot at which the read is performed.
  const SequenceNumber snapshot_ = kMaxSequenceNumber;
  // Any seq less than min_uncommitted_ is committed.
  const SequenceNumber min_uncommitted_ = 0;
};

}  //  namespace rocksdb