RocksDB counter example

rocksdb_counter_example.cc

// Copyright (c) 2013, Facebook, Inc.  All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
#include <cstdio>
#include <string>

#include "rocksdb/db.h"
#include "rocksdb/slice.h"
#include "rocksdb/options.h"
#include "../utilities/merge_operators.h"

using namespace rocksdb;

std::string kDBPath = "/tmp/rocksdb_counter_example";

inline void EncodeFixed64(char* buf, uint64_t value) {
#if __BYTE_ORDER == __LITTLE_ENDIAN
  memcpy(buf, &value, sizeof(value));
#else
  buf[0] = value & 0xff;
  buf[1] = (value >> 8) & 0xff;
  buf[2] = (value >> 16) & 0xff;
  buf[3] = (value >> 24) & 0xff;
  buf[4] = (value >> 32) & 0xff;
  buf[5] = (value >> 40) & 0xff;
  buf[6] = (value >> 48) & 0xff;
  buf[7] = (value >> 56) & 0xff;
#endif
}

inline uint32_t DecodeFixed32(const char* ptr) {
  #if __BYTE_ORDER == __LITTLE_ENDIAN
    // Load the raw bytes
    uint32_t result;
    memcpy(&result, ptr, sizeof(result));  // gcc optimizes this to a plain load
    return result;
#else
    return ((static_cast<uint32_t>(static_cast<unsigned char>(ptr[0])))
        | (static_cast<uint32_t>(static_cast<unsigned char>(ptr[1])) << 8)
        | (static_cast<uint32_t>(static_cast<unsigned char>(ptr[2])) << 16)
        | (static_cast<uint32_t>(static_cast<unsigned char>(ptr[3])) << 24));
#endif
}

inline uint64_t DecodeFixed64(const char* ptr) {
  #if __BYTE_ORDER == __LITTLE_ENDIAN
    // Load the raw bytes
    uint64_t result;
    memcpy(&result, ptr, sizeof(result));  // gcc optimizes this to a plain load
    return result;
#else
    uint64_t lo = DecodeFixed32(ptr);
    uint64_t hi = DecodeFixed32(ptr + 4);
    return (hi << 32) | lo;
#endif
}

int main() {
  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;
  options.merge_operator = (MergeOperators::CreateUInt64AddOperator());

  // open DB
  Status s = DB::Open(options, kDBPath, &db);
  assert(s.ok());

  uint64_t value = 1;
  for (int i=0; i < 1000000000; i++) {
    char encoded[sizeof(uint64_t)];
    EncodeFixed64(encoded, value);
    Slice slice(encoded, sizeof(uint64_t));
    db->Merge(WriteOptions(), Slice("key"), slice);
  }

  std::string retStr;
  // get value
  s = db->Get(ReadOptions(), "key", &retStr);
  assert(s.ok());
  assert(DecodeFixed64(retStr.c_str()) == 10000);

  delete db;
  return 0;
}