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 #ifdef HAS_ENDIAN_H
   9 #include <endian.h>
  10 #endif
  11 #include <fcntl.h>
  12 #include <string.h>
  13 #include <string_view>
  14 #include <sys/stat.h>
  15 #include <sys/time.h>
  16 #include <sys/types.h>
  17 #include <unistd.h>
  18 #include <zdict.h>
  19 #include <zstd.h>
  20
  21 #define P4NENC_BOUND(n) ((n + 127) / 128 + (n + 32) * sizeof(uint32_t))
  22
  23 #define NUM_TRIGRAMS 16777216
  24
  25 using namespace std;
  26 using namespace std::chrono;
  27
  28 constexpr unsigned num_overflow_slots = 16;
  29
  30 string zstd_compress(const string &src, ZSTD_CDict *cdict, string *tempbuf);
  31
  32 // NOTE: Will read one byte past the end of the trigram, but it's OK,
  33 // since we always call it from contexts where there's a terminating zero byte.
  34 static inline uint32_t read_trigram(const string_view s, size_t start)
  35 {
  36         uint32_t trgm;
  37         memcpy(&trgm, s.data() + start, sizeof(trgm));
  38         trgm = le32toh(trgm);
  39         return trgm & 0xffffff;
  40 }
  41
  42 class PostingListBuilder {
  43 public:
  44         inline void add_docid(uint32_t docid);
  45         inline void add_first_docid(uint32_t docid);
  46         void finish();
  47
  48         vector<unsigned char> encoded;
  49         size_t num_docids = 0;
  50
  51 private:
  52         void write_header(uint32_t docid);
  53         void append_block();
  54
  55         vector<uint32_t> pending_deltas;
  56
  57         uint32_t last_docid = -1;
  58 };
  59
  60 void PostingListBuilder::add_docid(uint32_t docid)
  61 {
  62         // Deduplicate against the last inserted value, if any.
  63         if (docid == last_docid) {
  64                 return;
  65         }
  66
  67         assert(num_docids != 0);
  68
  69         pending_deltas.push_back(docid - last_docid - 1);
  70         last_docid = docid;
  71         if (pending_deltas.size() == 128) {
  72                 append_block();
  73                 pending_deltas.clear();
  74         }
  75         ++num_docids;
  76 }
  77
  78 void PostingListBuilder::add_first_docid(uint32_t docid)
  79 {
  80         write_header(docid);
  81         ++num_docids;
  82         last_docid = docid;
  83 }
  84
  85 void PostingListBuilder::finish()
  86 {
  87         if (pending_deltas.empty()) {
  88                 return;
  89         }
  90
  91         assert(!encoded.empty());  // write_header() should already have run.
  92
  93         // No interleaving for partial blocks.
  94         unsigned char buf[P4NENC_BOUND(128)];
  95         unsigned char *end = encode_pfor_single_block<128>(pending_deltas.data(), pending_deltas.size(), /*interleaved=*/false, buf);
  96         encoded.insert(encoded.end(), buf, end);
  97 }
  98
  99 void PostingListBuilder::append_block()
 100 {
 101         unsigned char buf[P4NENC_BOUND(128)];
 102         assert(pending_deltas.size() == 128);
 103         unsigned char *end = encode_pfor_single_block<128>(pending_deltas.data(), 128, /*interleaved=*/true, buf);
 104         encoded.insert(encoded.end(), buf, end);
 105 }
 106
 107 void PostingListBuilder::write_header(uint32_t docid)
 108 {
 109         unsigned char buf[P4NENC_BOUND(1)];
 110         unsigned char *end = write_baseval(docid, buf);
 111         encoded.insert(encoded.end(), buf, end);
 112 }
 113
 114 void DictionaryBuilder::add_file(string filename, dir_time)
 115 {
 116         if (keep_current_block) {  // Only bother saving the filenames if we're actually keeping the block.
 117                 if (!current_block.empty()) {
 118                         current_block.push_back('\0');
 119                 }
 120                 current_block += filename;
 121         }
 122         if (++num_files_in_block == block_size) {
 123                 flush_block();
 124         }
 125 }
 126
 127 void DictionaryBuilder::flush_block()
 128 {
 129         if (keep_current_block) {
 130                 if (slot_for_current_block == -1) {
 131                         lengths.push_back(current_block.size());
 132                         sampled_blocks.push_back(move(current_block));
 133                 } else {
 134                         lengths[slot_for_current_block] = current_block.size();
 135                         sampled_blocks[slot_for_current_block] = move(current_block);
 136                 }
 137         }
 138         current_block.clear();
 139         num_files_in_block = 0;
 140         ++block_num;
 141
 142         if (block_num < blocks_to_keep) {
 143                 keep_current_block = true;
 144                 slot_for_current_block = -1;
 145         } else {
 146                 // Keep every block with equal probability (reservoir sampling).
 147                 uint64_t idx = uniform_int_distribution<uint64_t>(0, block_num)(reservoir_rand);
 148                 keep_current_block = (idx < blocks_to_keep);
 149                 slot_for_current_block = idx;
 150         }
 151 }
 152
 153 string DictionaryBuilder::train(size_t buf_size)
 154 {
 155         string dictionary_buf;
 156         sort(sampled_blocks.begin(), sampled_blocks.end());  // Seemingly important for decompression speed.
 157         for (const string &block : sampled_blocks) {
 158                 dictionary_buf += block;
 159         }
 160
 161         string buf;
 162         buf.resize(buf_size);
 163         size_t ret = ZDICT_trainFromBuffer(&buf[0], buf_size, dictionary_buf.data(), lengths.data(), lengths.size());
 164         if (ZDICT_isError(ret)) {
 165                 return "";
 166         }
 167         dprintf("Sampled %zu bytes in %zu blocks, built a dictionary of size %zu\n", dictionary_buf.size(), lengths.size(), ret);
 168         buf.resize(ret);
 169
 170         sampled_blocks.clear();
 171         lengths.clear();
 172
 173         return buf;
 174 }
 175
 176 class EncodingCorpus : public DatabaseReceiver {
 177 public:
 178         EncodingCorpus(FILE *outfp, size_t block_size, ZSTD_CDict *cdict, bool store_dir_times);
 179         ~EncodingCorpus();
 180
 181         void add_file(std::string filename, dir_time dt) override;
 182         void flush_block() override;
 183         void finish() override;
 184
 185         std::vector<uint64_t> filename_blocks;
 186         size_t num_files = 0, num_files_in_block = 0, num_blocks = 0;
 187         bool seen_trigram(uint32_t trgm)
 188         {
 189                 return invindex[trgm] != nullptr;
 190         }
 191         size_t num_files_seen() const override { return num_files; }
 192         PostingListBuilder &get_pl_builder(uint32_t trgm)
 193         {
 194                 return *invindex[trgm];
 195         }
 196
 197         void add_docid(uint32_t trgm, uint32_t docid)
 198         {
 199                 if (invindex[trgm] == nullptr) {
 200                         invindex[trgm] = new PostingListBuilder;
 201                         invindex[trgm]->add_first_docid(docid);
 202                 } else {
 203                         invindex[trgm]->add_docid(docid);
 204                 }
 205         }
 206
 207         size_t num_trigrams() const;
 208         std::string get_compressed_dir_times();
 209
 210 private:
 211         void compress_dir_times(size_t allowed_slop);
 212
 213         std::unique_ptr<PostingListBuilder *[]> invindex;
 214         FILE *outfp;
 215         std::string current_block;
 216         std::string tempbuf;
 217         const size_t block_size;
 218         const bool store_dir_times;
 219         ZSTD_CDict *cdict;
 220
 221         ZSTD_CStream *dir_time_ctx = nullptr;
 222         std::string dir_times;  // Buffer of still-uncompressed data.
 223         std::string dir_times_compressed;
 224 };
 225
 226
 227 EncodingCorpus::EncodingCorpus(FILE *outfp, size_t block_size, ZSTD_CDict *cdict, bool store_dir_times)
 228         : invindex(new PostingListBuilder *[NUM_TRIGRAMS]), outfp(outfp), block_size(block_size), store_dir_times(store_dir_times), cdict(cdict)
 229 {
 230         fill(invindex.get(), invindex.get() + NUM_TRIGRAMS, nullptr);
 231         if (store_dir_times) {
 232                 dir_time_ctx = ZSTD_createCStream();
 233                 ZSTD_initCStream(dir_time_ctx, /*level=*/6);
 234         }
 235 }
 236
 237 EncodingCorpus::~EncodingCorpus()
 238 {
 239         for (unsigned i = 0; i < NUM_TRIGRAMS; ++i) {
 240                 delete invindex[i];
 241         }
 242 }
 243
 244 void EncodingCorpus::add_file(string filename, dir_time dt)
 245 {
 246         ++num_files;
 247         if (!current_block.empty()) {
 248                 current_block.push_back('\0');
 249         }
 250         current_block += filename;
 251         if (++num_files_in_block == block_size) {
 252                 flush_block();
 253         }
 254
 255         if (store_dir_times) {
 256                 if (dt.sec == -1) {
 257                         // Not a directory.
 258                         dir_times.push_back('\0');
 259                 } else {
 260                         dir_times.push_back('\1');
 261                         dir_times.append(reinterpret_cast<char *>(&dt.sec), sizeof(dt.sec));
 262                         dir_times.append(reinterpret_cast<char *>(&dt.nsec), sizeof(dt.nsec));
 263                 }
 264                 compress_dir_times(/*allowed_slop=*/4096);
 265         }
 266 }
 267
 268 void EncodingCorpus::compress_dir_times(size_t allowed_slop)
 269 {
 270         while (dir_times.size() >= allowed_slop) {
 271                 size_t old_size = dir_times_compressed.size();
 272                 dir_times_compressed.resize(old_size + 4096);
 273
 274                 ZSTD_outBuffer outbuf;
 275                 outbuf.dst = dir_times_compressed.data() + old_size;
 276                 outbuf.size = 4096;
 277                 outbuf.pos = 0;
 278
 279                 ZSTD_inBuffer inbuf;
 280                 inbuf.src = dir_times.data();
 281                 inbuf.size = dir_times.size();
 282                 inbuf.pos = 0;
 283
 284                 int ret = ZSTD_compressStream(dir_time_ctx, &outbuf, &inbuf);
 285                 if (ret < 0) {
 286                         fprintf(stderr, "ZSTD_compressStream() failed\n");
 287                         exit(1);
 288                 }
 289
 290                 dir_times_compressed.resize(old_size + outbuf.pos);
 291                 dir_times.erase(dir_times.begin(), dir_times.begin() + inbuf.pos);
 292
 293                 if (outbuf.pos == 0 && inbuf.pos == 0) {
 294                         // Nothing happened (not enough data?), try again later.
 295                         return;
 296                 }
 297         }
 298 }
 299
 300 void EncodingCorpus::flush_block()
 301 {
 302         if (current_block.empty()) {
 303                 return;
 304         }
 305
 306         uint32_t docid = num_blocks;
 307
 308         // Create trigrams.
 309         const char *ptr = current_block.c_str();
 310         while (ptr < current_block.c_str() + current_block.size()) {
 311                 string_view s(ptr);
 312                 if (s.size() >= 3) {
 313                         for (size_t j = 0; j < s.size() - 2; ++j) {
 314                                 uint32_t trgm = read_trigram(s, j);
 315                                 add_docid(trgm, docid);
 316                         }
 317                 }
 318                 ptr += s.size() + 1;
 319         }
 320
 321         // Compress and add the filename block.
 322         filename_blocks.push_back(ftell(outfp));
 323         string compressed = zstd_compress(current_block, cdict, &tempbuf);
 324         if (fwrite(compressed.data(), compressed.size(), 1, outfp) != 1) {
 325                 perror("fwrite()");
 326                 exit(1);
 327         }
 328
 329         current_block.clear();
 330         num_files_in_block = 0;
 331         ++num_blocks;
 332 }
 333
 334 void EncodingCorpus::finish()
 335 {
 336         flush_block();
 337 }
 338
 339 size_t EncodingCorpus::num_trigrams() const
 340 {
 341         size_t num = 0;
 342         for (unsigned trgm = 0; trgm < NUM_TRIGRAMS; ++trgm) {
 343                 if (invindex[trgm] != nullptr) {
 344                         ++num;
 345                 }
 346         }
 347         return num;
 348 }
 349
 350 string EncodingCorpus::get_compressed_dir_times()
 351 {
 352         if (!store_dir_times) {
 353                 return "";
 354         }
 355         compress_dir_times(/*allowed_slop=*/0);
 356         assert(dir_times.empty());
 357
 358         for (;;) {
 359                 size_t old_size = dir_times_compressed.size();
 360                 dir_times_compressed.resize(old_size + 4096);
 361
 362                 ZSTD_outBuffer outbuf;
 363                 outbuf.dst = dir_times_compressed.data() + old_size;
 364                 outbuf.size = 4096;
 365                 outbuf.pos = 0;
 366
 367                 int ret = ZSTD_endStream(dir_time_ctx, &outbuf);
 368                 if (ret < 0) {
 369                         fprintf(stderr, "ZSTD_compressStream() failed\n");
 370                         exit(1);
 371                 }
 372
 373                 dir_times_compressed.resize(old_size + outbuf.pos);
 374
 375                 if (ret == 0) {
 376                         // All done.
 377                         break;
 378                 }
 379         }
 380
 381         return dir_times_compressed;
 382 }
 383
 384 string zstd_compress(const string &src, ZSTD_CDict *cdict, string *tempbuf)
 385 {
 386         static ZSTD_CCtx *ctx = nullptr;
 387         if (ctx == nullptr) {
 388                 ctx = ZSTD_createCCtx();
 389         }
 390
 391         size_t max_size = ZSTD_compressBound(src.size());
 392         if (tempbuf->size() < max_size) {
 393                 tempbuf->resize(max_size);
 394         }
 395         size_t size;
 396         if (cdict == nullptr) {
 397                 size = ZSTD_compressCCtx(ctx, &(*tempbuf)[0], max_size, src.data(), src.size(), /*level=*/6);
 398         } else {
 399                 size = ZSTD_compress_usingCDict(ctx, &(*tempbuf)[0], max_size, src.data(), src.size(), cdict);
 400         }
 401         return string(tempbuf->data(), size);
 402 }
 403
 404 bool is_prime(uint32_t x)
 405 {
 406         if ((x % 2) == 0 || (x % 3) == 0) {
 407                 return false;
 408         }
 409         uint32_t limit = ceil(sqrt(x));
 410         for (uint32_t factor = 5; factor <= limit; ++factor) {
 411                 if ((x % factor) == 0) {
 412                         return false;
 413                 }
 414         }
 415         return true;
 416 }
 417
 418 uint32_t next_prime(uint32_t x)
 419 {
 420         if ((x % 2) == 0) {
 421                 ++x;
 422         }
 423         while (!is_prime(x)) {
 424                 x += 2;
 425         }
 426         return x;
 427 }
 428
 429 unique_ptr<Trigram[]> create_hashtable(EncodingCorpus &corpus, const vector<uint32_t> &all_trigrams, uint32_t ht_size, uint32_t num_overflow_slots)
 430 {
 431         unique_ptr<Trigram[]> ht(new Trigram[ht_size + num_overflow_slots + 1]);  // 1 for the sentinel element at the end.
 432         for (unsigned i = 0; i < ht_size + num_overflow_slots + 1; ++i) {
 433                 ht[i].trgm = uint32_t(-1);
 434                 ht[i].num_docids = 0;
 435                 ht[i].offset = 0;
 436         }
 437         for (uint32_t trgm : all_trigrams) {
 438                 // We don't know offset yet, so set it to zero.
 439                 Trigram to_insert{ trgm, uint32_t(corpus.get_pl_builder(trgm).num_docids), 0 };
 440
 441                 uint32_t bucket = hash_trigram(trgm, ht_size);
 442                 unsigned distance = 0;
 443                 while (ht[bucket].num_docids != 0) {
 444                         // Robin Hood hashing; reduces the longest distance by a lot.
 445                         unsigned other_distance = bucket - hash_trigram(ht[bucket].trgm, ht_size);
 446                         if (distance > other_distance) {
 447                                 swap(to_insert, ht[bucket]);
 448                                 distance = other_distance;
 449                         }
 450
 451                         ++bucket, ++distance;
 452                         if (distance > num_overflow_slots) {
 453                                 return nullptr;
 454                         }
 455                 }
 456                 ht[bucket] = to_insert;
 457         }
 458         return ht;
 459 }
 460
 461 DatabaseBuilder::DatabaseBuilder(const char *outfile, gid_t owner, int block_size, string dictionary, bool check_visibility)
 462         : outfile(outfile), block_size(block_size)
 463 {
 464         umask(0027);
 465
 466         string path = outfile;
 467         path.resize(path.find_last_of('/') + 1);
 468         if (path.empty()) {
 469                 path = ".";
 470         }
 471 #ifdef O_TMPFILE
 472         int fd = open(path.c_str(), O_WRONLY | O_TMPFILE, 0640);
 473         if (fd == -1) {
 474                 perror(path.c_str());
 475                 exit(1);
 476         }
 477 #else
 478         temp_filename = string(outfile) + ".XXXXXX";
 479         int fd = mkstemp(&temp_filename[0]);
 480         if (fd == -1) {
 481                 perror(temp_filename.c_str());
 482                 exit(1);
 483         }
 484         if (fchmod(fd, 0640) == -1) {
 485                 perror("fchmod");
 486                 exit(1);
 487         }
 488 #endif
 489
 490         if (owner != (gid_t)-1) {
 491                 if (fchown(fd, (uid_t)-1, owner) == -1) {
 492                         perror("fchown");
 493                         exit(1);
 494                 }
 495         }
 496
 497         outfp = fdopen(fd, "wb");
 498         if (outfp == nullptr) {
 499                 perror(outfile);
 500                 exit(1);
 501         }
 502
 503         // Write the header.
 504         memcpy(hdr.magic, "\0plocate", 8);
 505         hdr.version = -1;  // Mark as broken.
 506         hdr.hashtable_size = 0;  // Not known yet.
 507         hdr.extra_ht_slots = num_overflow_slots;
 508         hdr.num_docids = 0;
 509         hdr.hash_table_offset_bytes = -1;  // We don't know these offsets yet.
 510         hdr.max_version = 2;
 511         hdr.filename_index_offset_bytes = -1;
 512         hdr.zstd_dictionary_length_bytes = -1;
 513         hdr.check_visibility = check_visibility;
 514         fwrite(&hdr, sizeof(hdr), 1, outfp);
 515
 516         if (dictionary.empty()) {
 517                 hdr.zstd_dictionary_offset_bytes = 0;
 518                 hdr.zstd_dictionary_length_bytes = 0;
 519         } else {
 520                 hdr.zstd_dictionary_offset_bytes = ftell(outfp);
 521                 fwrite(dictionary.data(), dictionary.size(), 1, outfp);
 522                 hdr.zstd_dictionary_length_bytes = dictionary.size();
 523                 cdict = ZSTD_createCDict(dictionary.data(), dictionary.size(), /*level=*/6);
 524         }
 525
 526         hdr.directory_data_length_bytes = 0;
 527         hdr.directory_data_offset_bytes = 0;
 528         hdr.next_zstd_dictionary_length_bytes = 0;
 529         hdr.next_zstd_dictionary_offset_bytes = 0;
 530         hdr.conf_block_length_bytes = 0;
 531         hdr.conf_block_offset_bytes = 0;
 532 }
 533
 534 DatabaseReceiver *DatabaseBuilder::start_corpus(bool store_dir_times)
 535 {
 536         corpus_start = steady_clock::now();
 537         corpus = new EncodingCorpus(outfp, block_size, cdict, store_dir_times);
 538         return corpus;
 539 }
 540
 541 void DatabaseBuilder::set_next_dictionary(std::string next_dictionary)
 542 {
 543         this->next_dictionary = move(next_dictionary);
 544 }
 545
 546 void DatabaseBuilder::set_conf_block(std::string conf_block)
 547 {
 548         this->conf_block = move(conf_block);
 549 }
 550
 551 void DatabaseBuilder::finish_corpus()
 552 {
 553         corpus->finish();
 554         hdr.num_docids = corpus->filename_blocks.size();
 555
 556         // Stick an empty block at the end as sentinel.
 557         corpus->filename_blocks.push_back(ftell(outfp));
 558         const size_t bytes_for_filenames = corpus->filename_blocks.back() - corpus->filename_blocks.front();
 559
 560         // Write the offsets to the filenames.
 561         hdr.filename_index_offset_bytes = ftell(outfp);
 562         const size_t bytes_for_filename_index = corpus->filename_blocks.size() * sizeof(uint64_t);
 563         fwrite(corpus->filename_blocks.data(), corpus->filename_blocks.size(), sizeof(uint64_t), outfp);
 564         corpus->filename_blocks.clear();
 565         corpus->filename_blocks.shrink_to_fit();
 566
 567         // Finish up encoding the posting lists.
 568         size_t trigrams = 0, longest_posting_list = 0;
 569         size_t bytes_for_posting_lists = 0;
 570         for (unsigned trgm = 0; trgm < NUM_TRIGRAMS; ++trgm) {
 571                 if (!corpus->seen_trigram(trgm))
 572                         continue;
 573                 PostingListBuilder &pl_builder = corpus->get_pl_builder(trgm);
 574                 pl_builder.finish();
 575                 longest_posting_list = max(longest_posting_list, pl_builder.num_docids);
 576                 trigrams += pl_builder.num_docids;
 577                 bytes_for_posting_lists += pl_builder.encoded.size();
 578         }
 579         size_t num_trigrams = corpus->num_trigrams();
 580         dprintf("%zu files, %zu different trigrams, %zu entries, avg len %.2f, longest %zu\n",
 581                 corpus->num_files, num_trigrams, trigrams, double(trigrams) / num_trigrams, longest_posting_list);
 582         dprintf("%zu bytes used for posting lists (%.2f bits/entry)\n", bytes_for_posting_lists, 8 * bytes_for_posting_lists / double(trigrams));
 583
 584         dprintf("Building posting lists took %.1f ms.\n\n", 1e3 * duration<float>(steady_clock::now() - corpus_start).count());
 585
 586         // Find the used trigrams.
 587         vector<uint32_t> all_trigrams;
 588         for (unsigned trgm = 0; trgm < NUM_TRIGRAMS; ++trgm) {
 589                 if (corpus->seen_trigram(trgm)) {
 590                         all_trigrams.push_back(trgm);
 591                 }
 592         }
 593
 594         // Create the hash table.
 595         unique_ptr<Trigram[]> hashtable;
 596         uint32_t ht_size = next_prime(all_trigrams.size());
 597         for (;;) {
 598                 hashtable = create_hashtable(*corpus, all_trigrams, ht_size, num_overflow_slots);
 599                 if (hashtable == nullptr) {
 600                         dprintf("Failed creating hash table of size %u, increasing by 5%% and trying again.\n", ht_size);
 601                         ht_size = next_prime(ht_size * 1.05);
 602                 } else {
 603                         dprintf("Created hash table of size %u.\n\n", ht_size);
 604                         break;
 605                 }
 606         }
 607
 608         // Find the offsets for each posting list.
 609         size_t bytes_for_hashtable = (ht_size + num_overflow_slots + 1) * sizeof(Trigram);
 610         uint64_t offset = ftell(outfp) + bytes_for_hashtable;
 611         for (unsigned i = 0; i < ht_size + num_overflow_slots + 1; ++i) {
 612                 hashtable[i].offset = offset;  // Needs to be there even for empty slots.
 613                 if (hashtable[i].num_docids == 0) {
 614                         continue;
 615                 }
 616
 617                 const vector<unsigned char> &encoded = corpus->get_pl_builder(hashtable[i].trgm).encoded;
 618                 offset += encoded.size();
 619         }
 620
 621         // Write the hash table.
 622         hdr.hash_table_offset_bytes = ftell(outfp);
 623         hdr.hashtable_size = ht_size;
 624         fwrite(hashtable.get(), ht_size + num_overflow_slots + 1, sizeof(Trigram), outfp);
 625
 626         // Write the actual posting lists.
 627         for (unsigned i = 0; i < ht_size + num_overflow_slots + 1; ++i) {
 628                 if (hashtable[i].num_docids == 0) {
 629                         continue;
 630                 }
 631                 const vector<unsigned char> &encoded = corpus->get_pl_builder(hashtable[i].trgm).encoded;
 632                 fwrite(encoded.data(), encoded.size(), 1, outfp);
 633         }
 634
 635         // Finally, write the directory times (for updatedb).
 636         string compressed_dir_times = corpus->get_compressed_dir_times();
 637         size_t bytes_for_compressed_dir_times = 0;
 638         if (!compressed_dir_times.empty()) {
 639                 hdr.directory_data_offset_bytes = ftell(outfp);
 640                 hdr.directory_data_length_bytes = compressed_dir_times.size();
 641                 fwrite(compressed_dir_times.data(), compressed_dir_times.size(), 1, outfp);
 642                 bytes_for_compressed_dir_times = compressed_dir_times.size();
 643                 compressed_dir_times.clear();
 644         }
 645
 646         // Write the recommended dictionary for next update.
 647         if (!next_dictionary.empty()) {
 648                 hdr.next_zstd_dictionary_offset_bytes = ftell(outfp);
 649                 hdr.next_zstd_dictionary_length_bytes = next_dictionary.size();
 650                 fwrite(next_dictionary.data(), next_dictionary.size(), 1, outfp);
 651         }
 652
 653         // And the configuration block.
 654         if (!conf_block.empty()) {
 655                 hdr.conf_block_offset_bytes = ftell(outfp);
 656                 hdr.conf_block_length_bytes = conf_block.size();
 657                 fwrite(conf_block.data(), conf_block.size(), 1, outfp);
 658         }
 659
 660         // Rewind, and write the updated header.
 661         hdr.version = 1;
 662         fseek(outfp, 0, SEEK_SET);
 663         fwrite(&hdr, sizeof(hdr), 1, outfp);
 664
 665 #ifdef O_TMPFILE
 666         // Give the file a proper name, making it visible in the file system.
 667         // TODO: It would be nice to be able to do this atomically, like with rename.
 668         unlink(outfile.c_str());
 669         char procpath[256];
 670         snprintf(procpath, sizeof(procpath), "/proc/self/fd/%d", fileno(outfp));
 671         if (linkat(AT_FDCWD, procpath, AT_FDCWD, outfile.c_str(), AT_SYMLINK_FOLLOW) == -1) {
 672                 perror("linkat");
 673                 exit(1);
 674         }
 675 #else
 676         if (rename(temp_filename.c_str(), outfile.c_str()) == -1) {
 677                 perror("rename");
 678                 exit(1);
 679         }
 680 #endif
 681
 682         fclose(outfp);
 683
 684         size_t total_bytes = (bytes_for_hashtable + bytes_for_posting_lists + bytes_for_filename_index + bytes_for_filenames + bytes_for_compressed_dir_times);
 685
 686         dprintf("Block size:     %7d files\n", block_size);
 687         dprintf("Dictionary:     %'7.1f MB\n", hdr.zstd_dictionary_length_bytes / 1048576.0);
 688         dprintf("Hash table:     %'7.1f MB\n", bytes_for_hashtable / 1048576.0);
 689         dprintf("Posting lists:  %'7.1f MB\n", bytes_for_posting_lists / 1048576.0);
 690         dprintf("Filename index: %'7.1f MB\n", bytes_for_filename_index / 1048576.0);
 691         dprintf("Filenames:      %'7.1f MB\n", bytes_for_filenames / 1048576.0);
 692         if (bytes_for_compressed_dir_times != 0) {
 693                 dprintf("Modify times:   %'7.1f MB\n", bytes_for_compressed_dir_times / 1048576.0);
 694         }
 695         dprintf("Total:          %'7.1f MB\n", total_bytes / 1048576.0);
 696         dprintf("\n");
 697 }