RocksDB源码分析之db_test LevelReopenWithFIFO

TEST_F(DBTest, LevelReopenWithFIFO) {
  const int kLevelCount = 4;
  const int kKeyCount = 5;
  const int kTotalSstFileCount = kLevelCount * kKeyCount;
  const int kCF = 1;

  Options options = CurrentOptions();
  // Config level0_file_num_compaction_trigger to prevent L0 files being
  // automatically compacted while we are constructing a LSM tree structure
  // to test multi-level FIFO compaction.
  options.level0_file_num_compaction_trigger = kKeyCount + 1;
  CreateAndReopenWithCF({"pikachu"}, options);

  // The expected number of files per level after each file creation.

  // 每次创建后，每个level有多少key/value键值对
  // 如[0][0]="0,0,0,1"  表示Level3有一个键值对
  const std::string expected_files_per_level[kLevelCount][kKeyCount] = {
      {"0,0,0,1", "0,0,0,2", "0,0,0,3", "0,0,0,4", "0,0,0,5"},
      {"0,0,1,5", "0,0,2,5", "0,0,3,5", "0,0,4,5", "0,0,5,5"},
      {"0,1,5,5", "0,2,5,5", "0,3,5,5", "0,4,5,5", "0,5,5,5"},
      {"1,5,5,5", "2,5,5,5", "3,5,5,5", "4,5,5,5", "5,5,5,5"},
  };

// 每个key在选中Level（最下面的level）对应的value
// [3][3]="[ d1, d2, d3 ]"  表示key=d  value在Level1 Level2 Level3 分别对应d1, d2, d3
  const std::string expected_entries[kKeyCount][kLevelCount + 1] = {
      {"[ ]", "[ a3 ]", "[ a2, a3 ]", "[ a1, a2, a3 ]", "[ a0, a1, a2, a3 ]"},
      {"[ ]", "[ b3 ]", "[ b2, b3 ]", "[ b1, b2, b3 ]", "[ b0, b1, b2, b3 ]"},
      {"[ ]", "[ c3 ]", "[ c2, c3 ]", "[ c1, c2, c3 ]", "[ c0, c1, c2, c3 ]"},
      {"[ ]", "[ d3 ]", "[ d2, d3 ]", "[ d1, d2, d3 ]", "[ d0, d1, d2, d3 ]"},
      {"[ ]", "[ e3 ]", "[ e2, e3 ]", "[ e1, e2, e3 ]", "[ e0, e1, e2, e3 ]"},
  };

  // The loop below creates the following LSM tree where each (k, v) pair
  // represents a file that contains that entry.  When a file is created,
  // the db is reopend with FIFO compaction and verified the LSM tree
  // structure is still the same.
  //
  // The resulting LSM tree will contain 5 different keys.  Each key as
  // 4 different versions, located in different level.
  //
  // L0:  (e, e0) (d, d0) (c, c0) (b, b0) (a, a0)
  // L1:  (a, a1) (b, b1) (c, c1) (d, d1) (e, e1)
  // L2:  (a, a2) (b, b2) (c, c2) (d, d2) (e, e2)
  // L3:  (a, a3) (b, b3) (c, c3) (d, d3) (e, e3)

  // 创建过程，put->flush->MoveFilesToLevel
  // 依次创建 a3 b3 c3 d3 e3 并移入Level3 
  for (int l = 0; l < kLevelCount; ++l) {
    int level = kLevelCount - 1 - l;
    for (int p = 0; p < kKeyCount; ++p) {
      std::string put_key = std::string(1, char('a' + p));
      ASSERT_OK(Put(kCF, put_key, put_key + std::to_string(level)));
      ASSERT_OK(Flush(kCF));
      ASSERT_OK(dbfull()->TEST_WaitForFlushMemTable());
      for (int g = 0; g < kKeyCount; ++g) {
        int entry_count = (p >= g) ? l + 1 : l;
        std::string get_key = std::string(1, char('a' + g));
        CheckAllEntriesWithFifoReopen(expected_entries[g][entry_count], get_key,
                                      kCF, {"pikachu"}, options);
      }
      if (level != 0) {
        MoveFilesToLevel(level, kCF);
        // MoveFilesToLevel 该列族数据库下 Level以上元素移到level ； level=3，则移动Level0元素到Level3
        for (int g = 0; g < kKeyCount; ++g) {
          int entry_count = (p >= g) ? l + 1 : l;
          std::string get_key = std::string(1, char('a' + g));
          CheckAllEntriesWithFifoReopen(expected_entries[g][entry_count],
                                        get_key, kCF, {"pikachu"}, options);
        }
      }
      ASSERT_EQ(expected_files_per_level[l][p], FilesPerLevel(kCF));
      // FilesPerLevel该列族数据库下每Level对应元素个数
    }
  }

  // The expected number of sst files in each level after each FIFO compaction
  // that deletes the oldest sst file.
  // 合并后每个Level对应key与value键值对个数
  // [3]="5,5,5,2"  两次合并后 Level3元素有2个
  const std::string expected_files_per_level_after_fifo[] = {
      "5,5,5,4", "5,5,5,3", "5,5,5,2", "5,5,5,1", "5,5,5", "5,5,4", "5,5,3",
      "5,5,2",   "5,5,1",   "5,5",     "5,4",     "5,3",   "5,2",   "5,1",
      "5",       "4",       "3",       "2",       "1",     "",
  };

  // The expected value entries of each key after each FIFO compaction.
  // This verifies whether FIFO removes the file with the smallest key in non-L0
  // files first then the oldest files in L0.
  // 合并后的每个key对应value个数，验证合并是先删除非Level0，然后是Level0的文件；
  const std::string expected_entries_after_fifo[kKeyCount][kLevelCount + 1] = {
      {"[ a0, a1, a2, a3 ]", "[ a0, a1, a2 ]", "[ a0, a1 ]", "[ a0 ]", "[ ]"},
      {"[ b0, b1, b2, b3 ]", "[ b0, b1, b2 ]", "[ b0, b1 ]", "[ b0 ]", "[ ]"},
      {"[ c0, c1, c2, c3 ]", "[ c0, c1, c2 ]", "[ c0, c1 ]", "[ c0 ]", "[ ]"},
      {"[ d0, d1, d2, d3 ]", "[ d0, d1, d2 ]", "[ d0, d1 ]", "[ d0 ]", "[ ]"},
      {"[ e0, e1, e2, e3 ]", "[ e0, e1, e2 ]", "[ e0, e1 ]", "[ e0 ]", "[ ]"},
  };

  // In the 2nd phase, we reopen the DB with FIFO compaction.  In each reopen,
  // we config max_table_files_size so that FIFO will remove exactly one file
  // at a time upon compaction, and we will use it to verify whether the sst
  // files are deleted in the correct order.
  
// 在第二阶段，我们使用FIFO压缩重新打开DB。在每次重新打开时，我们配置了max_table_files_size，这样FIFO将只删除一个文件一次压实后，我们将使用它来验证sst是否文件将按正确的顺序删除。 
  for (int i = 0; i < kTotalSstFileCount; ++i) {
    uint64_t total_sst_files_size = 0;
    ASSERT_TRUE(dbfull()->GetIntProperty(
        handles_[1], "rocksdb.total-sst-files-size", &total_sst_files_size));
    ASSERT_TRUE(total_sst_files_size > 0);

    Options fifo_options(options);
    fifo_options.compaction_style = kCompactionStyleFIFO;
    options.create_if_missing = false;
    fifo_options.max_open_files = -1;
    fifo_options.disable_auto_compactions = false;
    // Config max_table_files_size to be total_sst_files_size - 1 so that
    // FIFO will delete one file.
    fifo_options.compaction_options_fifo.max_table_files_size =
        total_sst_files_size - 1;
    ASSERT_OK(
        TryReopenWithColumnFamilies({"default", "pikachu"}, fifo_options));
    // For FIFO to pick a compaction
    ASSERT_OK(dbfull()->TEST_CompactRange(0, nullptr, nullptr, handles_[1]));
    ASSERT_OK(dbfull()->TEST_WaitForBackgroundWork());
    for (int g = 0; g < kKeyCount; ++g) {
      std::string get_key = std::string(1, char('a' + g));
      int status_index = i / kKeyCount;
      if ((i % kKeyCount) >= g) {
        // If true, then it means the sst file containing the get_key in the
        // current level has already been deleted, so we need to move the
        // status_index for checking the expected value.
        status_index++;
      }
      CheckAllEntriesWithFifoReopen(
          expected_entries_after_fifo[g][status_index], get_key, kCF,
          {"pikachu"}, options);
    }
    ASSERT_EQ(expected_files_per_level_after_fifo[i], FilesPerLevel(kCF));
  }
}