git.sesse.net Git - plocate/blob - database-builder.cpp

   1 #include "database-builder.h"
   2
   3 #include "dprintf.h"
   4 #include "turbopfor-encode.h"
   5
   6 #include <algorithm>
   7 #include <assert.h>
   8 #include <fcntl.h>
   9 #include <string.h>
  10 #include <string_view>
  11 #include <sys/stat.h>
  12 #include <sys/time.h>
  13 #include <sys/types.h>
  14 #include <unistd.h>
  15 #include <zdict.h>
  16 #include <zstd.h>
  17
  18 #define P4NENC_BOUND(n) ((n + 127) / 128 + (n + 32) * sizeof(uint32_t))
  19
  20 #define NUM_TRIGRAMS 16777216
  21
  22 using namespace std;
  23 using namespace std::chrono;
  24
  25 constexpr unsigned num_overflow_slots = 16;
  26
  27 string zstd_compress(const string &src, ZSTD_CDict *cdict, string *tempbuf);
  28
  29 static inline uint32_t read_unigram(const string_view s, size_t idx)
  30 {
  31         if (idx < s.size()) {
  32                 return (unsigned char)s[idx];
  33         } else {
  34                 return 0;
  35         }
  36 }
  37
  38 static inline uint32_t read_trigram(const string_view s, size_t start)
  39 {
  40         return read_unigram(s, start) |
  41                 (read_unigram(s, start + 1) << 8) |
  42                 (read_unigram(s, start + 2) << 16);
  43 }
  44
  45 class PostingListBuilder {
  46 public:
  47         inline void add_docid(uint32_t docid);
  48         inline void add_first_docid(uint32_t docid);
  49         void finish();
  50
  51         string encoded;
  52         size_t num_docids = 0;
  53
  54 private:
  55         void write_header(uint32_t docid);
  56         void append_block();
  57
  58         vector<uint32_t> pending_deltas;
  59
  60         uint32_t last_docid = -1;
  61 };
  62
  63 void PostingListBuilder::add_docid(uint32_t docid)
  64 {
  65         // Deduplicate against the last inserted value, if any.
  66         if (docid == last_docid) {
  67                 return;
  68         }
  69
  70         assert(num_docids != 0);
  71
  72         pending_deltas.push_back(docid - last_docid - 1);
  73         last_docid = docid;
  74         if (pending_deltas.size() == 128) {
  75                 append_block();
  76                 pending_deltas.clear();
  77         }
  78         ++num_docids;
  79 }
  80
  81 void PostingListBuilder::add_first_docid(uint32_t docid)
  82 {
  83         write_header(docid);
  84         ++num_docids;
  85         last_docid = docid;
  86 }
  87
  88 void PostingListBuilder::finish()
  89 {
  90         if (pending_deltas.empty()) {
  91                 return;
  92         }
  93
  94         assert(!encoded.empty());  // write_header() should already have run.
  95
  96         // No interleaving for partial blocks.
  97         unsigned char buf[P4NENC_BOUND(128)];
  98         unsigned char *end = encode_pfor_single_block<128>(pending_deltas.data(), pending_deltas.size(), /*interleaved=*/false, buf);
  99         encoded.append(reinterpret_cast<char *>(buf), reinterpret_cast<char *>(end));
 100 }
 101
 102 void PostingListBuilder::append_block()
 103 {
 104         unsigned char buf[P4NENC_BOUND(128)];
 105         assert(pending_deltas.size() == 128);
 106         unsigned char *end = encode_pfor_single_block<128>(pending_deltas.data(), 128, /*interleaved=*/true, buf);
 107         encoded.append(reinterpret_cast<char *>(buf), reinterpret_cast<char *>(end));
 108 }
 109
 110 void PostingListBuilder::write_header(uint32_t docid)
 111 {
 112         unsigned char buf[P4NENC_BOUND(1)];
 113         unsigned char *end = write_baseval(docid, buf);
 114         encoded.append(reinterpret_cast<char *>(buf), end - buf);
 115 }
 116
 117 void DictionaryBuilder::add_file(string filename, dir_time)
 118 {
 119         if (keep_current_block) {  // Only bother saving the filenames if we're actually keeping the block.
 120                 if (!current_block.empty()) {
 121                         current_block.push_back('\0');
 122                 }
 123                 current_block += filename;
 124         }
 125         if (++num_files_in_block == block_size) {
 126                 flush_block();
 127         }
 128 }
 129
 130 void DictionaryBuilder::flush_block()
 131 {
 132         if (keep_current_block) {
 133                 if (slot_for_current_block == -1) {
 134                         lengths.push_back(current_block.size());
 135                         sampled_blocks.push_back(move(current_block));
 136                 } else {
 137                         lengths[slot_for_current_block] = current_block.size();
 138                         sampled_blocks[slot_for_current_block] = move(current_block);
 139                 }
 140         }
 141         current_block.clear();
 142         num_files_in_block = 0;
 143         ++block_num;
 144
 145         if (block_num < blocks_to_keep) {
 146                 keep_current_block = true;
 147                 slot_for_current_block = -1;
 148         } else {
 149                 // Keep every block with equal probability (reservoir sampling).
 150                 uint64_t idx = uniform_int_distribution<uint64_t>(0, block_num)(reservoir_rand);
 151                 keep_current_block = (idx < blocks_to_keep);
 152                 slot_for_current_block = idx;
 153         }
 154 }
 155
 156 string DictionaryBuilder::train(size_t buf_size)
 157 {
 158         string dictionary_buf;
 159         sort(sampled_blocks.begin(), sampled_blocks.end());  // Seemingly important for decompression speed.
 160         for (const string &block : sampled_blocks) {
 161                 dictionary_buf += block;
 162         }
 163
 164         string buf;
 165         buf.resize(buf_size);
 166         size_t ret = ZDICT_trainFromBuffer(&buf[0], buf_size, dictionary_buf.data(), lengths.data(), lengths.size());
 167         if (ZDICT_isError(ret)) {
 168                 return "";
 169         }
 170         dprintf("Sampled %zu bytes in %zu blocks, built a dictionary of size %zu\n", dictionary_buf.size(), lengths.size(), ret);
 171         buf.resize(ret);
 172
 173         sampled_blocks.clear();
 174         lengths.clear();
 175
 176         return buf;
 177 }
 178
 179 class EncodingCorpus : public DatabaseReceiver {
 180 public:
 181         EncodingCorpus(FILE *outfp, size_t block_size, ZSTD_CDict *cdict, bool store_dir_times);
 182         ~EncodingCorpus();
 183
 184         void add_file(std::string filename, dir_time dt) override;
 185         void flush_block() override;
 186         void finish() override;
 187
 188         std::vector<uint64_t> filename_blocks;
 189         size_t num_files = 0, num_files_in_block = 0, num_blocks = 0;
 190         bool seen_trigram(uint32_t trgm)
 191         {
 192                 return invindex[trgm] != nullptr;
 193         }
 194         size_t num_files_seen() const override { return num_files; }
 195         PostingListBuilder &get_pl_builder(uint32_t trgm)
 196         {
 197                 return *invindex[trgm];
 198         }
 199
 200         void add_docid(uint32_t trgm, uint32_t docid)
 201         {
 202                 if (invindex[trgm] == nullptr) {
 203                         invindex[trgm] = new PostingListBuilder;
 204                         invindex[trgm]->add_first_docid(docid);
 205                 } else {
 206                         invindex[trgm]->add_docid(docid);
 207                 }
 208         }
 209
 210         size_t num_trigrams() const;
 211         std::string get_compressed_dir_times();
 212
 213 private:
 214         void compress_dir_times(size_t allowed_slop);
 215
 216         std::unique_ptr<PostingListBuilder *[]> invindex;
 217         FILE *outfp;
 218         std::string current_block;
 219         std::string tempbuf;
 220         const size_t block_size;
 221         const bool store_dir_times;
 222         ZSTD_CDict *cdict;
 223
 224         ZSTD_CStream *dir_time_ctx = nullptr;
 225         std::string dir_times;  // Buffer of still-uncompressed data.
 226         std::string dir_times_compressed;
 227 };
 228
 229
 230 EncodingCorpus::EncodingCorpus(FILE *outfp, size_t block_size, ZSTD_CDict *cdict, bool store_dir_times)
 231         : invindex(new PostingListBuilder *[NUM_TRIGRAMS]), outfp(outfp), block_size(block_size), store_dir_times(store_dir_times), cdict(cdict)
 232 {
 233         fill(invindex.get(), invindex.get() + NUM_TRIGRAMS, nullptr);
 234         if (store_dir_times) {
 235                 dir_time_ctx = ZSTD_createCStream();
 236                 ZSTD_initCStream(dir_time_ctx, /*level=*/6);
 237         }
 238 }
 239
 240 EncodingCorpus::~EncodingCorpus()
 241 {
 242         for (unsigned i = 0; i < NUM_TRIGRAMS; ++i) {
 243                 delete invindex[i];
 244         }
 245 }
 246
 247 void EncodingCorpus::add_file(string filename, dir_time dt)
 248 {
 249         ++num_files;
 250         if (!current_block.empty()) {
 251                 current_block.push_back('\0');
 252         }
 253         current_block += filename;
 254         if (++num_files_in_block == block_size) {
 255                 flush_block();
 256         }
 257
 258         if (store_dir_times) {
 259                 if (dt.sec == -1) {
 260                         // Not a directory.
 261                         dir_times.push_back('\0');
 262                 } else {
 263                         dir_times.push_back('\1');
 264                         dir_times.append(reinterpret_cast<char *>(&dt.sec), sizeof(dt.sec));
 265                         dir_times.append(reinterpret_cast<char *>(&dt.nsec), sizeof(dt.nsec));
 266                 }
 267                 compress_dir_times(/*allowed_slop=*/4096);
 268         }
 269 }
 270
 271 void EncodingCorpus::compress_dir_times(size_t allowed_slop)
 272 {
 273         while (dir_times.size() >= allowed_slop) {
 274                 size_t old_size = dir_times_compressed.size();
 275                 dir_times_compressed.resize(old_size + 4096);
 276
 277                 ZSTD_outBuffer outbuf;
 278                 outbuf.dst = dir_times_compressed.data() + old_size;
 279                 outbuf.size = 4096;
 280                 outbuf.pos = 0;
 281
 282                 ZSTD_inBuffer inbuf;
 283                 inbuf.src = dir_times.data();
 284                 inbuf.size = dir_times.size();
 285                 inbuf.pos = 0;
 286
 287                 int ret = ZSTD_compressStream(dir_time_ctx, &outbuf, &inbuf);
 288                 if (ret < 0) {
 289                         fprintf(stderr, "ZSTD_compressStream() failed\n");
 290                         exit(1);
 291                 }
 292
 293                 dir_times_compressed.resize(old_size + outbuf.pos);
 294                 dir_times.erase(dir_times.begin(), dir_times.begin() + inbuf.pos);
 295
 296                 if (outbuf.pos == 0 && inbuf.pos == 0) {
 297                         // Nothing happened (not enough data?), try again later.
 298                         return;
 299                 }
 300         }
 301 }
 302
 303 void EncodingCorpus::flush_block()
 304 {
 305         if (current_block.empty()) {
 306                 return;
 307         }
 308
 309         uint32_t docid = num_blocks;
 310
 311         // Create trigrams.
 312         const char *ptr = current_block.c_str();
 313         while (ptr < current_block.c_str() + current_block.size()) {
 314                 string_view s(ptr);
 315                 if (s.size() >= 3) {
 316                         for (size_t j = 0; j < s.size() - 2; ++j) {
 317                                 uint32_t trgm = read_trigram(s, j);
 318                                 add_docid(trgm, docid);
 319                         }
 320                 }
 321                 ptr += s.size() + 1;
 322         }
 323
 324         // Compress and add the filename block.
 325         filename_blocks.push_back(ftell(outfp));
 326         string compressed = zstd_compress(current_block, cdict, &tempbuf);
 327         if (fwrite(compressed.data(), compressed.size(), 1, outfp) != 1) {
 328                 perror("fwrite()");
 329                 exit(1);
 330         }
 331
 332         current_block.clear();
 333         num_files_in_block = 0;
 334         ++num_blocks;
 335 }
 336
 337 void EncodingCorpus::finish()
 338 {
 339         flush_block();
 340 }
 341
 342 size_t EncodingCorpus::num_trigrams() const
 343 {
 344         size_t num = 0;
 345         for (unsigned trgm = 0; trgm < NUM_TRIGRAMS; ++trgm) {
 346                 if (invindex[trgm] != nullptr) {
 347                         ++num;
 348                 }
 349         }
 350         return num;
 351 }
 352
 353 string EncodingCorpus::get_compressed_dir_times()
 354 {
 355         if (!store_dir_times) {
 356                 return "";
 357         }
 358         compress_dir_times(/*allowed_slop=*/0);
 359         assert(dir_times.empty());
 360
 361         for (;;) {
 362                 size_t old_size = dir_times_compressed.size();
 363                 dir_times_compressed.resize(old_size + 4096);
 364
 365                 ZSTD_outBuffer outbuf;
 366                 outbuf.dst = dir_times_compressed.data() + old_size;
 367                 outbuf.size = 4096;
 368                 outbuf.pos = 0;
 369
 370                 int ret = ZSTD_endStream(dir_time_ctx, &outbuf);
 371                 if (ret < 0) {
 372                         fprintf(stderr, "ZSTD_compressStream() failed\n");
 373                         exit(1);
 374                 }
 375
 376                 dir_times_compressed.resize(old_size + outbuf.pos);
 377
 378                 if (ret == 0) {
 379                         // All done.
 380                         break;
 381                 }
 382         }
 383
 384         return dir_times_compressed;
 385 }
 386
 387 string zstd_compress(const string &src, ZSTD_CDict *cdict, string *tempbuf)
 388 {
 389         static ZSTD_CCtx *ctx = nullptr;
 390         if (ctx == nullptr) {
 391                 ctx = ZSTD_createCCtx();
 392         }
 393
 394         size_t max_size = ZSTD_compressBound(src.size());
 395         if (tempbuf->size() < max_size) {
 396                 tempbuf->resize(max_size);
 397         }
 398         size_t size;
 399         if (cdict == nullptr) {
 400                 size = ZSTD_compressCCtx(ctx, &(*tempbuf)[0], max_size, src.data(), src.size(), /*level=*/6);
 401         } else {
 402                 size = ZSTD_compress_usingCDict(ctx, &(*tempbuf)[0], max_size, src.data(), src.size(), cdict);
 403         }
 404         return string(tempbuf->data(), size);
 405 }
 406
 407 bool is_prime(uint32_t x)
 408 {
 409         if ((x % 2) == 0 || (x % 3) == 0) {
 410                 return false;
 411         }
 412         uint32_t limit = ceil(sqrt(x));
 413         for (uint32_t factor = 5; factor <= limit; ++factor) {
 414                 if ((x % factor) == 0) {
 415                         return false;
 416                 }
 417         }
 418         return true;
 419 }
 420
 421 uint32_t next_prime(uint32_t x)
 422 {
 423         if ((x % 2) == 0) {
 424                 ++x;
 425         }
 426         while (!is_prime(x)) {
 427                 x += 2;
 428         }
 429         return x;
 430 }
 431
 432 unique_ptr<Trigram[]> create_hashtable(EncodingCorpus &corpus, const vector<uint32_t> &all_trigrams, uint32_t ht_size, uint32_t num_overflow_slots)
 433 {
 434         unique_ptr<Trigram[]> ht(new Trigram[ht_size + num_overflow_slots + 1]);  // 1 for the sentinel element at the end.
 435         for (unsigned i = 0; i < ht_size + num_overflow_slots + 1; ++i) {
 436                 ht[i].trgm = uint32_t(-1);
 437                 ht[i].num_docids = 0;
 438                 ht[i].offset = 0;
 439         }
 440         for (uint32_t trgm : all_trigrams) {
 441                 // We don't know offset yet, so set it to zero.
 442                 Trigram to_insert{ trgm, uint32_t(corpus.get_pl_builder(trgm).num_docids), 0 };
 443
 444                 uint32_t bucket = hash_trigram(trgm, ht_size);
 445                 unsigned distance = 0;
 446                 while (ht[bucket].num_docids != 0) {
 447                         // Robin Hood hashing; reduces the longest distance by a lot.
 448                         unsigned other_distance = bucket - hash_trigram(ht[bucket].trgm, ht_size);
 449                         if (distance > other_distance) {
 450                                 swap(to_insert, ht[bucket]);
 451                                 distance = other_distance;
 452                         }
 453
 454                         ++bucket, ++distance;
 455                         if (distance > num_overflow_slots) {
 456                                 return nullptr;
 457                         }
 458                 }
 459                 ht[bucket] = to_insert;
 460         }
 461         return ht;
 462 }
 463
 464 DatabaseBuilder::DatabaseBuilder(const char *outfile, gid_t owner, int block_size, string dictionary, bool check_visibility)
 465         : outfile(outfile), block_size(block_size)
 466 {
 467         umask(0027);
 468
 469         string path = outfile;
 470         path.resize(path.find_last_of('/') + 1);
 471         if (path.empty()) {
 472                 path = ".";
 473         }
 474 #ifdef O_TMPFILE
 475         int fd = open(path.c_str(), O_WRONLY | O_TMPFILE, 0640);
 476         if (fd == -1) {
 477                 perror(path.c_str());
 478                 exit(1);
 479         }
 480 #else
 481         temp_filename = string(outfile) + ".XXXXXX";
 482         int fd = mkstemp(&temp_filename[0]);
 483         if (fd == -1) {
 484                 perror(temp_filename.c_str());
 485                 exit(1);
 486         }
 487         if (fchmod(fd, 0640) == -1) {
 488                 perror("fchmod");
 489                 exit(1);
 490         }
 491 #endif
 492
 493         if (owner != (gid_t)-1) {
 494                 if (fchown(fd, (uid_t)-1, owner) == -1) {
 495                         perror("fchown");
 496                         exit(1);
 497                 }
 498         }
 499
 500         outfp = fdopen(fd, "wb");
 501         if (outfp == nullptr) {
 502                 perror(outfile);
 503                 exit(1);
 504         }
 505
 506         // Write the header.
 507         memcpy(hdr.magic, "\0plocate", 8);
 508         hdr.version = -1;  // Mark as broken.
 509         hdr.hashtable_size = 0;  // Not known yet.
 510         hdr.extra_ht_slots = num_overflow_slots;
 511         hdr.num_docids = 0;
 512         hdr.hash_table_offset_bytes = -1;  // We don't know these offsets yet.
 513         hdr.max_version = 2;
 514         hdr.filename_index_offset_bytes = -1;
 515         hdr.zstd_dictionary_length_bytes = -1;
 516         hdr.check_visibility = check_visibility;
 517         fwrite(&hdr, sizeof(hdr), 1, outfp);
 518
 519         if (dictionary.empty()) {
 520                 hdr.zstd_dictionary_offset_bytes = 0;
 521                 hdr.zstd_dictionary_length_bytes = 0;
 522         } else {
 523                 hdr.zstd_dictionary_offset_bytes = ftell(outfp);
 524                 fwrite(dictionary.data(), dictionary.size(), 1, outfp);
 525                 hdr.zstd_dictionary_length_bytes = dictionary.size();
 526                 cdict = ZSTD_createCDict(dictionary.data(), dictionary.size(), /*level=*/6);
 527         }
 528
 529         hdr.directory_data_length_bytes = 0;
 530         hdr.directory_data_offset_bytes = 0;
 531         hdr.next_zstd_dictionary_length_bytes = 0;
 532         hdr.next_zstd_dictionary_offset_bytes = 0;
 533         hdr.conf_block_length_bytes = 0;
 534         hdr.conf_block_offset_bytes = 0;
 535 }
 536
 537 DatabaseReceiver *DatabaseBuilder::start_corpus(bool store_dir_times)
 538 {
 539         corpus_start = steady_clock::now();
 540         corpus = new EncodingCorpus(outfp, block_size, cdict, store_dir_times);
 541         return corpus;
 542 }
 543
 544 void DatabaseBuilder::set_next_dictionary(std::string next_dictionary)
 545 {
 546         this->next_dictionary = move(next_dictionary);
 547 }
 548
 549 void DatabaseBuilder::set_conf_block(std::string conf_block)
 550 {
 551         this->conf_block = move(conf_block);
 552 }
 553
 554 void DatabaseBuilder::finish_corpus()
 555 {
 556         corpus->finish();
 557         hdr.num_docids = corpus->filename_blocks.size();
 558
 559         // Stick an empty block at the end as sentinel.
 560         corpus->filename_blocks.push_back(ftell(outfp));
 561         const size_t bytes_for_filenames = corpus->filename_blocks.back() - corpus->filename_blocks.front();
 562
 563         // Write the offsets to the filenames.
 564         hdr.filename_index_offset_bytes = ftell(outfp);
 565         const size_t bytes_for_filename_index = corpus->filename_blocks.size() * sizeof(uint64_t);
 566         fwrite(corpus->filename_blocks.data(), corpus->filename_blocks.size(), sizeof(uint64_t), outfp);
 567         corpus->filename_blocks.clear();
 568         corpus->filename_blocks.shrink_to_fit();
 569
 570         // Finish up encoding the posting lists.
 571         size_t trigrams = 0, longest_posting_list = 0;
 572         size_t bytes_for_posting_lists = 0;
 573         for (unsigned trgm = 0; trgm < NUM_TRIGRAMS; ++trgm) {
 574                 if (!corpus->seen_trigram(trgm))
 575                         continue;
 576                 PostingListBuilder &pl_builder = corpus->get_pl_builder(trgm);
 577                 pl_builder.finish();
 578                 longest_posting_list = max(longest_posting_list, pl_builder.num_docids);
 579                 trigrams += pl_builder.num_docids;
 580                 bytes_for_posting_lists += pl_builder.encoded.size();
 581         }
 582         size_t num_trigrams = corpus->num_trigrams();
 583         dprintf("%zu files, %zu different trigrams, %zu entries, avg len %.2f, longest %zu\n",
 584                 corpus->num_files, num_trigrams, trigrams, double(trigrams) / num_trigrams, longest_posting_list);
 585         dprintf("%zu bytes used for posting lists (%.2f bits/entry)\n", bytes_for_posting_lists, 8 * bytes_for_posting_lists / double(trigrams));
 586
 587         dprintf("Building posting lists took %.1f ms.\n\n", 1e3 * duration<float>(steady_clock::now() - corpus_start).count());
 588
 589         // Find the used trigrams.
 590         vector<uint32_t> all_trigrams;
 591         for (unsigned trgm = 0; trgm < NUM_TRIGRAMS; ++trgm) {
 592                 if (corpus->seen_trigram(trgm)) {
 593                         all_trigrams.push_back(trgm);
 594                 }
 595         }
 596
 597         // Create the hash table.
 598         unique_ptr<Trigram[]> hashtable;
 599         uint32_t ht_size = next_prime(all_trigrams.size());
 600         for (;;) {
 601                 hashtable = create_hashtable(*corpus, all_trigrams, ht_size, num_overflow_slots);
 602                 if (hashtable == nullptr) {
 603                         dprintf("Failed creating hash table of size %u, increasing by 5%% and trying again.\n", ht_size);
 604                         ht_size = next_prime(ht_size * 1.05);
 605                 } else {
 606                         dprintf("Created hash table of size %u.\n\n", ht_size);
 607                         break;
 608                 }
 609         }
 610
 611         // Find the offsets for each posting list.
 612         size_t bytes_for_hashtable = (ht_size + num_overflow_slots + 1) * sizeof(Trigram);
 613         uint64_t offset = ftell(outfp) + bytes_for_hashtable;
 614         for (unsigned i = 0; i < ht_size + num_overflow_slots + 1; ++i) {
 615                 hashtable[i].offset = offset;  // Needs to be there even for empty slots.
 616                 if (hashtable[i].num_docids == 0) {
 617                         continue;
 618                 }
 619
 620                 const string &encoded = corpus->get_pl_builder(hashtable[i].trgm).encoded;
 621                 offset += encoded.size();
 622         }
 623
 624         // Write the hash table.
 625         hdr.hash_table_offset_bytes = ftell(outfp);
 626         hdr.hashtable_size = ht_size;
 627         fwrite(hashtable.get(), ht_size + num_overflow_slots + 1, sizeof(Trigram), outfp);
 628
 629         // Write the actual posting lists.
 630         for (unsigned i = 0; i < ht_size + num_overflow_slots + 1; ++i) {
 631                 if (hashtable[i].num_docids == 0) {
 632                         continue;
 633                 }
 634                 const string &encoded = corpus->get_pl_builder(hashtable[i].trgm).encoded;
 635                 fwrite(encoded.data(), encoded.size(), 1, outfp);
 636         }
 637
 638         // Finally, write the directory times (for updatedb).
 639         string compressed_dir_times = corpus->get_compressed_dir_times();
 640         size_t bytes_for_compressed_dir_times = 0;
 641         if (!compressed_dir_times.empty()) {
 642                 hdr.directory_data_offset_bytes = ftell(outfp);
 643                 hdr.directory_data_length_bytes = compressed_dir_times.size();
 644                 fwrite(compressed_dir_times.data(), compressed_dir_times.size(), 1, outfp);
 645                 bytes_for_compressed_dir_times = compressed_dir_times.size();
 646                 compressed_dir_times.clear();
 647         }
 648
 649         // Write the recommended dictionary for next update.
 650         if (!next_dictionary.empty()) {
 651                 hdr.next_zstd_dictionary_offset_bytes = ftell(outfp);
 652                 hdr.next_zstd_dictionary_length_bytes = next_dictionary.size();
 653                 fwrite(next_dictionary.data(), next_dictionary.size(), 1, outfp);
 654         }
 655
 656         // And the configuration block.
 657         if (!conf_block.empty()) {
 658                 hdr.conf_block_offset_bytes = ftell(outfp);
 659                 hdr.conf_block_length_bytes = conf_block.size();
 660                 fwrite(conf_block.data(), conf_block.size(), 1, outfp);
 661         }
 662
 663         // Rewind, and write the updated header.
 664         hdr.version = 1;
 665         fseek(outfp, 0, SEEK_SET);
 666         fwrite(&hdr, sizeof(hdr), 1, outfp);
 667
 668 #ifdef O_TMPFILE
 669         // Give the file a proper name, making it visible in the file system.
 670         // TODO: It would be nice to be able to do this atomically, like with rename.
 671         unlink(outfile.c_str());
 672         char procpath[256];
 673         snprintf(procpath, sizeof(procpath), "/proc/self/fd/%d", fileno(outfp));
 674         if (linkat(AT_FDCWD, procpath, AT_FDCWD, outfile.c_str(), AT_SYMLINK_FOLLOW) == -1) {
 675                 perror("linkat");
 676                 exit(1);
 677         }
 678 #else
 679         if (rename(temp_filename.c_str(), outfile.c_str()) == -1) {
 680                 perror("rename");
 681                 exit(1);
 682         }
 683 #endif
 684
 685         fclose(outfp);
 686
 687         size_t total_bytes = (bytes_for_hashtable + bytes_for_posting_lists + bytes_for_filename_index + bytes_for_filenames + bytes_for_compressed_dir_times);
 688
 689         dprintf("Block size:     %7d files\n", block_size);
 690         dprintf("Dictionary:     %'7.1f MB\n", hdr.zstd_dictionary_length_bytes / 1048576.0);
 691         dprintf("Hash table:     %'7.1f MB\n", bytes_for_hashtable / 1048576.0);
 692         dprintf("Posting lists:  %'7.1f MB\n", bytes_for_posting_lists / 1048576.0);
 693         dprintf("Filename index: %'7.1f MB\n", bytes_for_filename_index / 1048576.0);
 694         dprintf("Filenames:      %'7.1f MB\n", bytes_for_filenames / 1048576.0);
 695         if (bytes_for_compressed_dir_times != 0) {
 696                 dprintf("Modify times:   %'7.1f MB\n", bytes_for_compressed_dir_times / 1048576.0);
 697         }
 698         dprintf("Total:          %'7.1f MB\n", total_bytes / 1048576.0);
 699         dprintf("\n");
 700 }