rocksdb/db/perf_context_test.cc

#include <algorithm>
#include <iostream>
#include <vector>

#include "rocksdb/db.h"
#include "rocksdb/perf_context.h"
#include "util/histogram.h"
#include "util/stop_watch.h"
#include "util/testharness.h"

bool FLAGS_random_key = false;
int FLAGS_total_keys = 100;
int FLAGS_write_buffer_size = 1000000000;
int FLAGS_max_write_buffer_number = 8;
int FLAGS_min_write_buffer_number_to_merge = 7;

// Path to the database on file system
const std::string kDbName = leveldb::test::TmpDir() + "/perf_context_test";

namespace leveldb {

std::shared_ptr<DB> OpenDb() {
    DB* db;
    Options options;
    options.create_if_missing = true;
    options.write_buffer_size = FLAGS_write_buffer_size;
    options.max_write_buffer_number = FLAGS_max_write_buffer_number;
    options.min_write_buffer_number_to_merge =
      FLAGS_min_write_buffer_number_to_merge;
    Status s = DB::Open(options, kDbName,  &db);
    ASSERT_OK(s);
    return std::shared_ptr<DB>(db);
}

class PerfContextTest { };

TEST(PerfContextTest, StopWatchNanoOverhead) {
  // profile the timer cost by itself!
  const int kTotalIterations = 1000000;
  std::vector<uint64_t> timings(kTotalIterations);

  StopWatchNano timer(Env::Default(), true);
  for (auto& timing : timings) {
    timing = timer.ElapsedNanos(true /* reset */);
  }

  HistogramImpl histogram;
  for (const auto timing : timings) {
    histogram.Add(timing);
  }

  std::cout << histogram.ToString();
}

TEST(PerfContextTest, StopWatchOverhead) {
  // profile the timer cost by itself!
  const int kTotalIterations = 1000000;
  std::vector<uint64_t> timings(kTotalIterations);

  StopWatch timer(Env::Default());
  for (auto& timing : timings) {
    timing = timer.ElapsedMicros();
  }

  HistogramImpl histogram;
  uint64_t prev_timing = 0;
  for (const auto timing : timings) {
    histogram.Add(timing - prev_timing);
    prev_timing = timing;
  }

  std::cout << histogram.ToString();
}

void ProfileKeyComparison() {
  DestroyDB(kDbName, Options());    // Start this test with a fresh DB

  auto db = OpenDb();

  WriteOptions write_options;
  ReadOptions read_options;

  uint64_t total_user_key_comparison_get = 0;
  uint64_t total_user_key_comparison_put = 0;
  uint64_t max_user_key_comparison_get = 0;

  std::cout << "Inserting " << FLAGS_total_keys << " key/value pairs\n...\n";

  for (int i = 0; i < FLAGS_total_keys; ++i) {
    std::string key = "k" + std::to_string(i);
    std::string value = "v" + std::to_string(i);

    perf_context.Reset();
    db->Put(write_options, key, value);
    total_user_key_comparison_put += perf_context.user_key_comparison_count;

    perf_context.Reset();
    db->Get(read_options, key, &value);
    total_user_key_comparison_get += perf_context.user_key_comparison_count;
    max_user_key_comparison_get =
      std::max(max_user_key_comparison_get,
               perf_context.user_key_comparison_count);
  }

  std::cout << "total user key comparison get: "
            << total_user_key_comparison_get << "\n"
            << "total user key comparison put: "
            << total_user_key_comparison_put << "\n"
            << "max user key comparison get: "
            << max_user_key_comparison_get << "\n"
            << "avg user key comparison get:"
            << total_user_key_comparison_get/FLAGS_total_keys << "\n";

}

TEST(PerfContextTest, KeyComparisonCount) {
  SetPerfLevel(kEnableCount);
  ProfileKeyComparison();

  SetPerfLevel(kDisable);
  ProfileKeyComparison();

  SetPerfLevel(kEnableTime);
  ProfileKeyComparison();
}

// make perf_context_test
// export LEVELDB_TESTS=PerfContextTest.SeekKeyComparison
// For one memtable:
// ./perf_context_test --write_buffer_size=500000 --total_keys=10000
// For two memtables:
// ./perf_context_test --write_buffer_size=250000 --total_keys=10000
// Specify --random_key=1 to shuffle the key before insertion
// Results show that, for sequential insertion, worst-case Seek Key comparison
// is close to the total number of keys (linear), when there is only one
// memtable. When there are two memtables, even the avg Seek Key comparison
// starts to become linear to the input size.

TEST(PerfContextTest, SeekKeyComparison) {
  DestroyDB(kDbName, Options());
  auto db = OpenDb();
  WriteOptions write_options;
  ReadOptions read_options;

  std::cout << "Inserting " << FLAGS_total_keys << " key/value pairs\n...\n";

  std::vector<int> keys;
  for (int i = 0; i < FLAGS_total_keys; ++i) {
    keys.push_back(i);
  }

  if (FLAGS_random_key) {
    std::random_shuffle(keys.begin(), keys.end());
  }

  for (const int i : keys) {
    std::string key = "k" + std::to_string(i);
    std::string value = "v" + std::to_string(i);

    db->Put(write_options, key, value);
  }

  HistogramImpl histogram;
  for (int i = 0; i < FLAGS_total_keys; ++i) {
    std::string key = "k" + std::to_string(i);
    std::string value = "v" + std::to_string(i);

    std::unique_ptr<Iterator> iter(db->NewIterator(read_options));
    perf_context.Reset();
    iter->Seek(key);
    ASSERT_TRUE(iter->Valid());
    ASSERT_EQ(iter->value().ToString(), value);
    histogram.Add(perf_context.user_key_comparison_count);
  }
  std::cout << histogram.ToString();
}

}

int main(int argc, char** argv) {

  for (int i = 1; i < argc; i++) {
    int n;
    char junk;

    if (sscanf(argv[i], "--write_buffer_size=%d%c", &n, &junk) == 1) {
      FLAGS_write_buffer_size = n;
    }

    if (sscanf(argv[i], "--total_keys=%d%c", &n, &junk) == 1) {
      FLAGS_total_keys = n;
    }

    if (sscanf(argv[i], "--random_key=%d%c", &n, &junk) == 1 &&
        (n == 0 || n == 1)) {
      FLAGS_random_key = n;
    }

  }

  std::cout << kDbName << "\n";

  leveldb::test::RunAllTests();
  return 0;
}