[Public API Change] Make DB::GetDbIdentity() be const function.

Summary: Make DB::GetDbIdentity() be const function.

Test Plan: make db_test

Reviewers: igor, rven, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D38745

HISTORY.md

@@ -1,5 +1,8 @@
 # Rocksdb Change Log
 
+## Public API changes
+* DB::GetDbIdentity() is now a const function.  If this function is overridden in your application, be sure to also make GetDbIdentity() const to avoid compile error.
+
 ## 3.11.0 (5/19/2015)
 
 ### New Features

db/db_impl.cc

@@ -3820,7 +3820,7 @@ Status DBImpl::CheckConsistency() {
   }
 }
 
-Status DBImpl::GetDbIdentity(std::string& identity) {
+Status DBImpl::GetDbIdentity(std::string& identity) const {
   std::string idfilename = IdentityFileName(dbname_);
   unique_ptr<SequentialFile> idfile;
   const EnvOptions soptions;

db/db_impl.h

@@ -197,7 +197,7 @@ class DBImpl : public DB {
   // match to our in-memory records
   virtual Status CheckConsistency();
 
-  virtual Status GetDbIdentity(std::string& identity) override;
+  virtual Status GetDbIdentity(std::string& identity) const override;
 
   Status RunManualCompaction(ColumnFamilyData* cfd, int input_level,
                              int output_level, uint32_t output_path_id,

db/db_test.cc

@@ -8797,7 +8797,7 @@ class ModelDB: public DB {
 
   virtual Status DeleteFile(std::string name) override { return Status::OK(); }
 
-  virtual Status GetDbIdentity(std::string& identity) override {
+  virtual Status GetDbIdentity(std::string& identity) const override {
     return Status::OK();
   }
 

include/rocksdb/db.h

@@ -590,7 +590,7 @@ class DB {
   // Sets the globally unique ID created at database creation time by invoking
   // Env::GenerateUniqueId(), in identity. Returns Status::OK if identity could
   // be set properly
-  virtual Status GetDbIdentity(std::string& identity) = 0;
+  virtual Status GetDbIdentity(std::string& identity) const = 0;
 
   // Returns default column family handle
   virtual ColumnFamilyHandle* DefaultColumnFamily() const = 0;

include/rocksdb/utilities/stackable_db.h

@@ -226,7 +226,7 @@ class StackableDB : public DB {
     return db_->DeleteFile(name);
   }
 
-  virtual Status GetDbIdentity(std::string& identity) override {
+  virtual Status GetDbIdentity(std::string& identity) const override {
     return db_->GetDbIdentity(identity);
   }