ceph/src/rocksdb/db/read_callback.h

   1 // Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
   2 //  This source code is licensed under both the GPLv2 (found in the
   3 //  COPYING file in the root directory) and Apache 2.0 License
   4 //  (found in the LICENSE.Apache file in the root directory).
   5
   6 #pragma once
   7
   8 #include "rocksdb/types.h"
   9
  10 namespace rocksdb {
  11
  12 class ReadCallback {
  13  public:
  14   ReadCallback(SequenceNumber last_visible_seq)
  15       : max_visible_seq_(last_visible_seq) {}
  16   ReadCallback(SequenceNumber last_visible_seq, SequenceNumber min_uncommitted)
  17       : max_visible_seq_(last_visible_seq), min_uncommitted_(min_uncommitted) {}
  18
  19   virtual ~ReadCallback() {}
  20
  21   // Will be called to see if the seq number visible; if not it moves on to
  22   // the next seq number.
  23   virtual bool IsVisibleFullCheck(SequenceNumber seq) = 0;
  24
  25   inline bool IsVisible(SequenceNumber seq) {
  26     assert(min_uncommitted_ > 0);
  27     assert(min_uncommitted_ >= kMinUnCommittedSeq);
  28     if (seq < min_uncommitted_) {  // handles seq == 0 as well
  29       assert(seq <= max_visible_seq_);
  30       return true;
  31     } else if (max_visible_seq_ < seq) {
  32       assert(seq != 0);
  33       return false;
  34     } else {
  35       assert(seq != 0);  // already handled in the first if-then clause
  36       return IsVisibleFullCheck(seq);
  37     }
  38   }
  39
  40   inline SequenceNumber max_visible_seq() { return max_visible_seq_; }
  41
  42   virtual void Refresh(SequenceNumber seq) { max_visible_seq_ = seq; }
  43
  44   // Refer to DBIter::CanReseekToSkip
  45   virtual bool CanReseekToSkip() { return true; }
  46
  47  protected:
  48   // The max visible seq, it is usually the snapshot but could be larger if
  49   // transaction has its own writes written to db.
  50   SequenceNumber max_visible_seq_ = kMaxSequenceNumber;
  51   // Any seq less than min_uncommitted_ is committed.
  52   const SequenceNumber min_uncommitted_ = kMinUnCommittedSeq;
  53 };
  54
  55 }  //  namespace rocksdb