Optional sequence number exporting during checkpoint creation (facebook#5528)

Summary:
Add sequence_number_ptr to the checkpoint interface to expose the sequence number during taking the checkpoint. The number will be consistent with the seq # in rocksdb log.
Pull Request resolved: facebook#5528

Test Plan: make check -j64

Reviewed By: Winger1994

Differential Revision: D16080209

fbshipit-source-id: 6dc3c7680287ee97d673c5e61f89aae1f43e33df

Author: Chao Zhao

include/rocksdb/utilities/checkpoint.h

@@ -37,8 +37,12 @@ class Checkpoint {
   // away from the default, the checkpoint may not contain up-to-date data
   // if WAL writing is not always enabled.
   // Flush will always trigger if it is 2PC.
+  // sequence_number_ptr: if it is not nullptr, the value it points to will be
+  // set to the DB's sequence number. The default value of this parameter is
+  // nullptr.
   virtual Status CreateCheckpoint(const std::string& checkpoint_dir,
-                                  uint64_t log_size_for_flush = 0);
+                                  uint64_t log_size_for_flush = 0,
+                                  uint64_t* sequence_number_ptr = nullptr);
 
   // Exports all live SST files of a specified Column Family onto export_dir,
   // returning SST files information in metadata.

utilities/checkpoint/checkpoint_impl.cc

@@ -35,7 +35,8 @@ Status Checkpoint::Create(DB* db, Checkpoint** checkpoint_ptr) {
 }
 
 Status Checkpoint::CreateCheckpoint(const std::string& /*checkpoint_dir*/,
-                                    uint64_t /*log_size_for_flush*/) {
+                                    uint64_t /*log_size_for_flush*/,
+                                    uint64_t* /*sequence_number_ptr*/) {
   return Status::NotSupported("");
 }
 
@@ -69,7 +70,8 @@ Status Checkpoint::ExportColumnFamily(
 
 // Builds an openable snapshot of RocksDB
 Status CheckpointImpl::CreateCheckpoint(const std::string& checkpoint_dir,
-                                        uint64_t log_size_for_flush) {
+                                        uint64_t log_size_for_flush,
+                                        uint64_t* sequence_number_ptr) {
   DBOptions db_options = db_->GetDBOptions();
 
   Status s = db_->GetEnv()->FileExists(checkpoint_dir);
@@ -145,6 +147,9 @@ Status CheckpointImpl::CreateCheckpoint(const std::string& checkpoint_dir,
   }
 
   if (s.ok()) {
+    if (sequence_number_ptr != nullptr) {
+      *sequence_number_ptr = sequence_number;
+    }
     // here we know that we succeeded and installed the new snapshot
     ROCKS_LOG_INFO(db_options.info_log, "Snapshot DONE. All is good");
     ROCKS_LOG_INFO(db_options.info_log, "Snapshot sequence number: %" PRIu64,

utilities/checkpoint/checkpoint_impl.h

@@ -28,7 +28,8 @@ class CheckpointImpl : public Checkpoint {
   // The directory will be an absolute path
   using Checkpoint::CreateCheckpoint;
   virtual Status CreateCheckpoint(const std::string& checkpoint_dir,
-                                  uint64_t log_size_for_flush) override;
+                                  uint64_t log_size_for_flush,
+                                  uint64_t* sequence_number_ptr) override;
 
   // Exports all live SST files of a specified Column Family onto export_dir
   // and returning SST files information in metadata.