Add DB Property "rocksdb.current_version_number"

Summary: Add a DB Property "rocksdb.current_version_number" for users to monitor version changes and stale iterators.

Test Plan: Add a unit test.

Reviewers: andrewkr, yhchiang, kradhakrishnan, IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D54927

db/db_properties_test.cc

@@ -90,6 +90,18 @@ TEST_F(DBPropertiesTest, Empty) {
   } while (ChangeOptions());
 }
 
+TEST_F(DBPropertiesTest, CurrentVersionNumber) {
+  uint64_t v1, v2, v3;
+  ASSERT_TRUE(dbfull()->GetIntProperty("rocksdb.current_version_number", &v1));
+  Put("12345678", "");
+  ASSERT_TRUE(dbfull()->GetIntProperty("rocksdb.current_version_number", &v2));
+  Flush();
+  ASSERT_TRUE(dbfull()->GetIntProperty("rocksdb.current_version_number", &v3));
+
+  ASSERT_EQ(v1, v2);
+  ASSERT_GT(v3, v2);
+}
+
 TEST_F(DBPropertiesTest, GetAggregatedIntPropertyTest) {
   const int kKeySize = 100;
   const int kValueSize = 500;

db/internal_stats.cc

@@ -132,6 +132,7 @@ static const std::string is_file_deletions_enabled =
 static const std::string num_snapshots = "num-snapshots";
 static const std::string oldest_snapshot_time = "oldest-snapshot-time";
 static const std::string num_live_versions = "num-live-versions";
+static const std::string current_version_number = "current_version_number";
 static const std::string estimate_live_data_size = "estimate-live-data-size";
 static const std::string base_level = "base-level";
 static const std::string total_sst_files_size = "total-sst-files-size";
@@ -191,6 +192,8 @@ const std::string DB::Properties::kOldestSnapshotTime =
                       rocksdb_prefix + oldest_snapshot_time;
 const std::string DB::Properties::kNumLiveVersions =
                       rocksdb_prefix + num_live_versions;
+const std::string DB::Properties::kCurrentVersionNumber =
+    rocksdb_prefix + current_version_number;
 const std::string DB::Properties::kEstimateLiveDataSize =
                       rocksdb_prefix + estimate_live_data_size;
 const std::string DB::Properties::kTotalSstFilesSize =
@@ -254,6 +257,8 @@ const std::unordered_map<std::string,
      {false, nullptr, &InternalStats::HandleOldestSnapshotTime}},
     {DB::Properties::kNumLiveVersions,
      {false, nullptr, &InternalStats::HandleNumLiveVersions}},
+    {DB::Properties::kCurrentVersionNumber,
+     {false, nullptr, &InternalStats::HandleCurrentVersionNumber}},
     {DB::Properties::kEstimateLiveDataSize,
      {true, nullptr, &InternalStats::HandleEstimateLiveDataSize}},
     {DB::Properties::kBaseLevel,
@@ -519,6 +524,12 @@ bool InternalStats::HandleNumLiveVersions(uint64_t* value, DBImpl* db,
   return true;
 }
 
+bool InternalStats::HandleCurrentVersionNumber(uint64_t* value, DBImpl* db,
+                                               Version* version) {
+  *value = cfd_->GetSuperVersionNumber();
+  return true;
+}
+
 bool InternalStats::HandleIsFileDeletionsEnabled(uint64_t* value, DBImpl* db,
                                                  Version* version) {
   *value = db->IsFileDeletionsEnabled();

db/internal_stats.h

@@ -328,6 +328,8 @@ class InternalStats {
   bool HandleNumSnapshots(uint64_t* value, DBImpl* db, Version* version);
   bool HandleOldestSnapshotTime(uint64_t* value, DBImpl* db, Version* version);
   bool HandleNumLiveVersions(uint64_t* value, DBImpl* db, Version* version);
+  bool HandleCurrentVersionNumber(uint64_t* value, DBImpl* db,
+                                  Version* version);
   bool HandleIsFileDeletionsEnabled(uint64_t* value, DBImpl* db,
                                     Version* version);
   bool HandleBaseLevel(uint64_t* value, DBImpl* db, Version* version);

include/rocksdb/db.h

@@ -444,6 +444,9 @@ class DB {
     //      by iterators or unfinished compactions.
     static const std::string kNumLiveVersions;
 
+    //  "rocksdb.current-version-number" - returns number of curent LSM version.
+    static const std::string kCurrentVersionNumber;
+
     //  "rocksdb.estimate-live-data-size" - returns an estimate of the amount of
     //      live data in bytes.
     static const std::string kEstimateLiveDataSize;
@@ -504,6 +507,7 @@ class DB {
   //  "rocksdb.num-snapshots"
   //  "rocksdb.oldest-snapshot-time"
   //  "rocksdb.num-live-versions"
+  //  "rocksdb.current_version_number"
   //  "rocksdb.estimate-live-data-size"
   //  "rocksdb.total-sst-files-size"
   //  "rocksdb.base-level"