32-bit checksum is not enough to prevent ABA problem when multiple threads Get and Set same key

[ZiyanShi]

Bug Report

KVDK version

50fdd22

System configuration

2 * Intel(R) Xeon(R) Platinum 8269C CPU @ 2.50GHz
CPU: 2 * Intel(R) Xeon(R) Platinum 8269C CPU @ 2.50GHz
DDR: 12 * DDR4 16384 MB 2666 MT/s
PMEM: 4 * 129408 MB 2666 MT/s

Reproduce steps

Modify kv_engine.hpp

  inline uint64_t get_timestamp() {
    auto res = get_cpu_tsc() - ts_on_startup_ + newest_version_on_startup_;
    return res;
  }

to

  inline uint64_t get_timestamp() {
    return 0;
  }

Add test case to stress_test.cpp

TEST(HotspotTest, StringABATest)
{
    const std::string path_db{"/mnt/pmem0/kvdk_test_hotspot"};
    std::string cmd = "rm -rf " + path_db + "\n";
    int _sink = system(cmd.data());

    kvdk::Configs configs;
    configs.pmem_file_size = 1ULL << 30;
    configs.max_write_threads = 4;
    kvdk::Engine* engine = nullptr;
    kvdk::Engine::Open(path_db.data(), &engine, configs, stderr);  

    size_t n_skip = 636031;
    size_t v_size = (1ULL << 12);
    ProgressBar bar{std::cout, "", n_skip};
    for (size_t i = 0; i < n_skip; i++)
    {
        GetRandomString(v_size);
        bar.Update(i + 1);
    }    

    std::string key{"some_key"}; 
    key.resize(40);
    std::string zero_filled(v_size, 0);
    std::string value{GetRandomString(v_size)};
    for (size_t i = 3456; i < value.size(); i++)
      value[i] = 0;

    engine->Set(key, zero_filled);
    auto SetOrGet = [&](size_t tid)
    {
      size_t n_iteration = (1ULL << 20);
      if (tid % 2 == 0)
      {
        ProgressBar bar2{std::cout, "", n_iteration, (tid == 0)};
        for (size_t i = 0; i < n_iteration; i++)
        {
          EXPECT_EQ(engine->Set(key, zero_filled), kvdk::Status::Ok);
          EXPECT_EQ(engine->Set(key, value), kvdk::Status::Ok);
          if ((i + 1) % (1ULL << 10) == 0 && (tid == 0))
            bar2.Update(i + 1);         
        }
      }
      else
      {
        std::string value_got;
        for (size_t i = 0; i < n_iteration; i++)
        {
          EXPECT_EQ(engine->Get(key, &value_got), kvdk::Status::Ok);
          ASSERT_TRUE(value_got == zero_filled || value_got == value) 
            << "Got invalid value: \n"
            << value_got << "\n"
            << "Expected: \n"
            << value << std::endl;
        }
      }
    };
    LaunchNThreads(4, SetOrGet);

    _sink = system(cmd.data());
}

Build as Release and run

./build/dbstress_test --gtest_filter="*ABA*" --gtest_break_on_failure --gtest_catch_exceptions=1 --gtest_repeat=-1

Expect behavior

Test case success

Current behavior

Test case fail

Note

This test case is found by birthday attack.
get_timestamp() is fixed to return 0 to help reproduce the issue.

[Jiayu Wu]

resolved with mvcc #163