1 files changed, 54 insertions, 0 deletions
diff --git a/src/rocksdb/db/read_callback.h b/src/rocksdb/db/read_callback.h
new file mode 100644
index 000000000..c042352db
--- /dev/null
+++ b/src/rocksdb/db/read_callback.h
@@ -0,0 +1,54 @@
+// 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 "db/dbformat.h"
+#include "rocksdb/types.h"
+
+namespace ROCKSDB_NAMESPACE {
+
+class ReadCallback {
+ public:
+  explicit ReadCallback(SequenceNumber last_visible_seq)
+      : max_visible_seq_(last_visible_seq) {}
+  ReadCallback(SequenceNumber last_visible_seq, SequenceNumber min_uncommitted)
+      : max_visible_seq_(last_visible_seq), 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) {
+    assert(min_uncommitted_ > 0);
+    assert(min_uncommitted_ >= kMinUnCommittedSeq);
+    if (seq < min_uncommitted_) {  // handles seq == 0 as well
+      assert(seq <= max_visible_seq_);
+      return true;
+    } else if (max_visible_seq_ < seq) {
+      assert(seq != 0);
+      return false;
+    } else {
+      assert(seq != 0);  // already handled in the first if-then clause
+      return IsVisibleFullCheck(seq);
+    }
+  }
+
+  inline SequenceNumber max_visible_seq() { return max_visible_seq_; }
+
+  // Refresh to a more recent visible seq
+  virtual void Refresh(SequenceNumber seq) { max_visible_seq_ = seq; }
+
+ protected:
+  // The max visible seq, it is usually the snapshot but could be larger if
+  // transaction has its own writes written to db.
+  SequenceNumber max_visible_seq_ = kMaxSequenceNumber;
+  // Any seq less than min_uncommitted_ is committed.
+  const SequenceNumber min_uncommitted_ = kMinUnCommittedSeq;
+};
+
+}  // namespace ROCKSDB_NAMESPACE