From 6c6037f60cfc1b4c2bc59391eddefaf3c766b8b7 Mon Sep 17 00:00:00 2001
From: Igor Canadi <icanadi@fb.com>
Date: Thu, 29 Jan 2015 18:22:43 -0800
Subject: [PATCH] Expose Snapshot's SequenceNumber

Summary:
Requested here: https://www.facebook.com/groups/rocksdb.dev/permalink/705524519546065/

It might also help with mongo. I don't see a reason why we shouldn't expose this info.

Test Plan: make check

Reviewers: sdong, yhchiang, rven

Reviewed By: rven

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D32547
---
 db/db_test.cc        | 6 ++++++
 db/snapshot.h        | 2 ++
 include/rocksdb/db.h | 4 ++++
 3 files changed, 12 insertions(+)

diff --git a/db/db_test.cc b/db/db_test.cc
index a8973a102..5941dc2d2 100644
--- a/db/db_test.cc
+++ b/db/db_test.cc
@@ -7751,6 +7751,12 @@ class ModelDB: public DB {
   class ModelSnapshot : public Snapshot {
    public:
     KVMap map_;
+
+    virtual SequenceNumber GetSequenceNumber() const {
+      // no need to call this
+      assert(false);
+      return 0;
+    }
   };
 
   explicit ModelDB(const Options& options) : options_(options) {}
diff --git a/db/snapshot.h b/db/snapshot.h
index 45c66eabc..de9897f24 100644
--- a/db/snapshot.h
+++ b/db/snapshot.h
@@ -20,6 +20,8 @@ class SnapshotImpl : public Snapshot {
  public:
   SequenceNumber number_;  // const after creation
 
+  virtual SequenceNumber GetSequenceNumber() const { return number_; }
+
  private:
   friend class SnapshotList;
 
diff --git a/include/rocksdb/db.h b/include/rocksdb/db.h
index a519db7f6..a4141f38b 100644
--- a/include/rocksdb/db.h
+++ b/include/rocksdb/db.h
@@ -64,6 +64,10 @@ static const int kMinorVersion = __ROCKSDB_MINOR__;
 // A Snapshot is an immutable object and can therefore be safely
 // accessed from multiple threads without any external synchronization.
 class Snapshot {
+ public:
+  // returns Snapshot's sequence number
+  virtual SequenceNumber GetSequenceNumber() const = 0;
+
  protected:
   virtual ~Snapshot();
 };