xref: /recipes/topk/word_freq_shards_basic.cc

/* sort word by frequency, sharding version.

  1. read input file, shard to N files:
       word
  2. assume each shard file fits in memory, read each shard file, count words and sort by count, then write to N count files:
       count \t word
  3. merge N count files using heap.

Limits: each shard must fit in memory.
*/

#include <assert.h>

#include <algorithm>
#include <fstream>
#include <iostream>
#include <memory>
#include <string>
#include <unordered_map>
#include <vector>

#include <fcntl.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/time.h>
#include <unistd.h>

using std::string;
using std::string_view;
using std::vector;
using std::unique_ptr;

int kShards = 10;

inline double now()
{
  struct timeval tv = { 0, 0 };
  gettimeofday(&tv, nullptr);
  return tv.tv_sec + tv.tv_usec / 1000000.0;
}

class OutputFile // : boost::noncopyable
{
 public:
  explicit OutputFile(const string& filename)
    : file_(::fopen(filename.c_str(), "w+"))
  {
    assert(file_);
    ::setbuffer(file_, buffer_, sizeof buffer_);
  }

  ~OutputFile()
  {
    close();
  }

  void append(string_view s)
  {
    assert(s.size() < 255);
    uint8_t len = s.size();
    ::fwrite(&len, 1, sizeof len, file_);
    ::fwrite(s.data(), 1, len, file_);
    ++items_;
  }

  /*
  void append(uint64_t x)
  {
    // FIXME: htobe64(x);
    ::fwrite(&x, 1, sizeof x, file_);
  }
  */

  void flush()
  {
    ::fflush(file_);
  }

  void close()
  {
    if (file_)
      ::fclose(file_);
    file_ = nullptr;
  }

  int64_t tell()
  {
    return ::ftell(file_);
  }

  int fd()
  {
    return ::fileno(file_);
  }

  size_t items()
  {
    return items_;
  }

 private:
  FILE* file_;
  char buffer_[64 * 1024];
  size_t items_ = 0;

  OutputFile(const OutputFile&) = delete;
  void operator=(const OutputFile&) = delete;
};

class Sharder // : boost::noncopyable
{
 public:
  Sharder()
    : files_(kShards)
  {
    for (int i = 0; i < kShards; ++i)
    {
      char name[256];
      snprintf(name, sizeof name, "shard-%05d-of-%05d", i, kShards);
      files_[i].reset(new OutputFile(name));
    }
    assert(files_.size() == static_cast<size_t>(kShards));
  }

  void output(string_view word)
  {
    size_t shard = hash(word) % files_.size();
    files_[shard]->append(word);
  }

  void finish()
  {
    for (int i = 0; i < files_.size(); ++i)
    {
      printf("shard %d: %ld bytes, %ld items\n", i, files_[i]->tell(), files_[i]->items());
    }
  }

 private:
  std::hash<string_view> hash;
  vector<unique_ptr<OutputFile>> files_;
};

void shard(int argc, char* argv[])
{
  Sharder sharder;
  double t = now();
  for (int i = 1; i < argc; ++i)
  {
    std::cout << "  processing input file " << argv[i] << std::endl;
    double t = now();
    char line[1024];
    FILE* fp = fopen(argv[i], "r");
    char buffer[65536];
    ::setbuffer(fp, buffer, sizeof buffer);
    while (fgets(line, sizeof line, fp))
    {
      size_t len = strlen(line);
      if (len > 0 && line[len-1] == '\n')
        line[len-1] = '\0';
      sharder.output(line);
    }
    size_t total = ftell(fp);
    fclose(fp);
    double sec = now() - t;
    printf("%.3f sec %.2f MB/s\n", sec, total / sec / 1000 / 1000);
  }
  sharder.finish();
  std::cout << "shuffling done " << now() - t << " sec" << std::endl;
}

// ======= count_shards =======

void count_shard(int shard, int fd)
{
  const int64_t len = lseek(fd, 0, SEEK_END);
  lseek(fd, 0, SEEK_SET);
  double t = now();
  printf("shard %d: file size %ld\n", shard, len);
  void* mapped = mmap(NULL, len, PROT_READ, MAP_PRIVATE, fd, 0);
  assert(mapped != MAP_FAILED);
  const uint8_t* const start = static_cast<const uint8_t*>(mapped);
  const uint8_t* const end = start + len;

  std::unordered_map<string_view, uint64_t> items;
  for (const uint8_t* p = start; p < end;)
  {
    string_view s((const char*)p+1, *p);
    items[s]++;
    p += 1 + *p;
  }
  printf("  count %.3f sec %ld items\n", now() - t, items.size());

  t = now();
  vector<std::pair<size_t, string_view>> counts;
  for (const auto& it : items)
  {
    if (it.second > 1)
      counts.push_back(make_pair(it.second, it.first));
  }
  printf("  select %.3f sec %ld\n", now() - t, counts.size());

  t = now();
  std::sort(counts.begin(), counts.end());
  printf("  sort %.3f sec\n", now() - t);

  t = now();
  char buf[256];
  snprintf(buf, sizeof buf, "count-%05d-of-%05d", shard, kShards);
  std::ofstream out(buf);
  for (auto it = counts.rbegin(); it != counts.rend(); ++it)
  {
    out << it->first << '\t' << it->second << '\n';
  }
  for (const auto& it : items)
  {
    if (it.second == 1)
    {
      out << "1\t" << it.first << '\n';
    }
  }
  printf("  output %.3f sec\n", now() - t);

  if (munmap(mapped, len))
    perror("munmap");
}

void count_shards()
{
  double t = now();
  for (int shard = 0; shard < kShards; ++shard)
  {
    char buf[256];
    snprintf(buf, sizeof buf, "shard-%05d-of-%05d", shard, kShards);
    int fd = open(buf, O_RDONLY);
    count_shard(shard, fd);
    ::close(fd);
    ::unlink(buf);
  }
  std::cout << "count done " << now() - t << " sec\n";
}

// ======= merge =======

class Source  // copyable
{
 public:
  explicit Source(std::istream* in)
    : in_(in),
      count_(0),
      word_()
  {
  }

  bool next()
  {
    string line;
    if (getline(*in_, line))
    {
      size_t tab = line.find('\t');
      if (tab != string::npos)
      {
        count_ = strtol(line.c_str(), NULL, 10);
        if (count_ > 0)
        {
          word_ = line.substr(tab+1);
          return true;
        }
      }
    }
    return false;
  }

  bool operator<(const Source& rhs) const
  {
    return count_ < rhs.count_;
  }

  void outputTo(std::ostream& out) const
  {
    out << count_ << '\t' << word_ << '\n';
  }

 private:
  std::istream* in_;
  int64_t count_;
  string word_;
};

void merge()
{
  vector<unique_ptr<std::ifstream>> inputs;
  vector<Source> keys;

  double t = now();
  for (int i = 0; i < kShards; ++i)
  {
    char buf[256];
    snprintf(buf, sizeof buf, "count-%05d-of-%05d", i, kShards);
    inputs.emplace_back(new std::ifstream(buf));
    Source rec(inputs.back().get());
    if (rec.next())
    {
      keys.push_back(rec);
    }
    ::unlink(buf);
  }

  std::ofstream out("output");
  std::make_heap(keys.begin(), keys.end());
  while (!keys.empty())
  {
    std::pop_heap(keys.begin(), keys.end());
    keys.back().outputTo(out);

    if (keys.back().next())
    {
      std::push_heap(keys.begin(), keys.end());
    }
    else
    {
      keys.pop_back();
    }
  }
  std::cout << "merging done " << now() - t << " sec\n";
}

int main(int argc, char* argv[])
{
  /*
  kShards = 9;
  int fd = open("shard-00000-of-00010", O_RDONLY);
  double t = now();
  sort_shard(0, fd, 1074462684, 100030936);
  printf("sort_shard %.3f sec\n", now() - t);
  t = now();
  count_shard(1, fd);
  printf("count_shard %.3f sec\n", now() - t);
  /*/

  shard(argc, argv);
  count_shards();
  merge();
  //*/
}