Add rocksDB merging code

tools/rocksDB_merger/rocksDB_merger.cc

+/*
+ *	Author : Ashwin <ashwin2007ray@gmail.com>
+ *
+ *	compile : g++ rocks_merge.cc <path_to_rocksDB_installation>/librocksdb.so.4.1 --std=c++11 -lstdc++fs
+ *	usage : ./<executable> <folder_having_rocksDB_directories_to_be_merged> <destinatnion_folder>
+ *
+ */
+
+#include <fstream>
+#include <cstdio>
+#include <iostream>
+#include <string>
+
+#include "rocksdb/db.h"
+#include "rocksdb/slice.h"
+#include "rocksdb/options.h"
+
+#include <experimental/filesystem>
+
+using namespace rocksdb;
+namespace fs = std::experimental::filesystem;
+
+int main(int argc, char* argv[]) {
+	if(argc != 3) {
+		std::cerr << "Wrong number of arguments\nusage : ./<executable> <folder_having_rocksDB_directories_to_be_merged> <destinatnion_folder>\n";
+		return 1;
+	}
+	std::string kDBPath = argv[2];
+	DB* db;
+  	Options options;
+    	// Optimize RocksDB. This is the easiest way to get RocksDB to perform well
+    	options.IncreaseParallelism();
+    	options.OptimizeLevelStyleCompaction();
+    	// create the DB if it's not already present
+	options.create_if_missing = true;
+             
+    	// open DB
+ 	Status s = DB::Open(options, kDBPath, &db);
+  	assert(s.ok());
+
+	for (auto& dirEntry : fs::directory_iterator(argv[1])) {
+		std::cout << dirEntry << "\n" ;
+	
+   	   	DB* cur_db;
+		Options options;
+    		options.IncreaseParallelism();
+    		options.OptimizeLevelStyleCompaction();
+    		// Don't create the DB if it's not already present
+		options.create_if_missing = false;
+             
+    		// open DB
+ 		Status s1 = DB::Open(options, dirEntry.path().c_str(), &cur_db);
+  		assert(s1.ok());
+	
+		rocksdb::Iterator* it = cur_db->NewIterator(rocksdb::ReadOptions());
+	    	for (it->SeekToFirst(); it->Valid(); it->Next()) {
+			std::cout << it->key().ToString() << ": " << it->value().ToString() << std::endl;
+			s = db->Put(WriteOptions(), it->key().ToString(), it->value().ToString());
+			assert(s.ok());
+		}
+	    	assert(it->status().ok()); // Check for any errors found during the scan
+	  	delete it;
+		delete cur_db;
+	}
+/*
+	rocksdb::Iterator* it = db->NewIterator(rocksdb::ReadOptions());	
+	for (it->SeekToFirst(); it->Valid(); it->Next()) {
+	         std::cout << it->key().ToString() << ": " << it->value().ToString() << std::endl;
+	}
+	assert(it->status().ok()); // Check for any errors found during the scan
+	delete it;
+*/
+	delete db;	
+	return 0;
+}