Expose the table properties to application

Summary: Provide a public API for users to access the table properties for each SSTable.

Test Plan: Added a unit tests to test the function correctness under differnet conditions.

Reviewers: haobo, dhruba, sdong

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16083

db/db_impl.cc

@@ -3488,6 +3488,23 @@ Status DBImpl::MakeRoomForWrite(bool force,
   return s;
 }
 
+Status DBImpl::GetPropertiesOfAllTables(TablePropertiesCollection* props) {
+  // Increment the ref count
+  mutex_.Lock();
+  auto version = versions_->current();
+  version->Ref();
+  mutex_.Unlock();
+
+  auto s = version->GetPropertiesOfAllTables(props);
+
+  // Decrement the ref count
+  mutex_.Lock();
+  version->Unref();
+  mutex_.Unlock();
+
+  return s;
+}
+
 const std::string& DBImpl::GetName() const {
   return dbname_;
 }