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 class PostingListBuilder {
  33 public:
  34         inline void add_docid(uint32_t docid);
  35         inline void add_first_docid(uint32_t docid);
  36         void finish();
  37
  38         vector<unsigned char> encoded;
  39         size_t get_num_docids() const {
  40                 // Updated only when we flush, so check that we're finished.
  41                 assert(pending_deltas.empty());
  42                 return num_docids;
  43         }
  44
  45 private:
  46         void write_header(uint32_t docid);
  47         void append_block();
  48
  49         vector<uint32_t> pending_deltas;
  50
  51         uint32_t num_docids = 0;  // Should be size_t, except the format only supports 2^32 docids per posting list anyway.
  52         uint32_t last_docid = -1;
  53 };
  54
  55 void PostingListBuilder::add_docid(uint32_t docid)
  56 {
  57         // Deduplicate against the last inserted value, if any.
  58         if (docid == last_docid) {
  59                 return;
  60         }
  61
  62         pending_deltas.push_back(docid - last_docid - 1);
  63         last_docid = docid;
  64         if (pending_deltas.size() == 128) {
  65                 append_block();
  66                 pending_deltas.clear();
  67                 num_docids += 128;
  68         }
  69 }
  70
  71 void PostingListBuilder::add_first_docid(uint32_t docid)
  72 {
  73         write_header(docid);
  74         ++num_docids;
  75         last_docid = docid;
  76 }
  77
  78 void PostingListBuilder::finish()
  79 {
  80         if (pending_deltas.empty()) {
  81                 return;
  82         }
  83
  84         assert(!encoded.empty());  // write_header() should already have run.
  85
  86         // No interleaving for partial blocks.
  87         unsigned char buf[P4NENC_BOUND(128)];
  88         unsigned char *end = encode_pfor_single_block<128>(pending_deltas.data(), pending_deltas.size(), /*interleaved=*/false, buf);
  89         encoded.insert(encoded.end(), buf, end);
  90
  91         num_docids += pending_deltas.size();
  92         pending_deltas.clear();
  93 }
  94
  95 void PostingListBuilder::append_block()
  96 {
  97         unsigned char buf[P4NENC_BOUND(128)];
  98         assert(pending_deltas.size() == 128);
  99         unsigned char *end = encode_pfor_single_block<128>(pending_deltas.data(), 128, /*interleaved=*/true, buf);
 100         encoded.insert(encoded.end(), buf, end);
 101 }
 102
 103 void PostingListBuilder::write_header(uint32_t docid)
 104 {
 105         unsigned char buf[P4NENC_BOUND(1)];
 106         unsigned char *end = write_baseval(docid, buf);
 107         encoded.insert(encoded.end(), buf, end);
 108 }
 109
 110 void DictionaryBuilder::add_file(string filename, dir_time)
 111 {
 112         if (keep_current_block) {  // Only bother saving the filenames if we're actually keeping the block.
 113                 if (!current_block.empty()) {
 114                         current_block.push_back('\0');
 115                 }
 116                 current_block += filename;
 117         }
 118         if (++num_files_in_block == block_size) {
 119                 flush_block();
 120         }
 121 }
 122
 123 void DictionaryBuilder::flush_block()
 124 {
 125         if (keep_current_block) {
 126                 if (slot_for_current_block == -1) {
 127                         lengths.push_back(current_block.size());
 128                         sampled_blocks.push_back(move(current_block));
 129                 } else {
 130                         lengths[slot_for_current_block] = current_block.size();
 131                         sampled_blocks[slot_for_current_block] = move(current_block);
 132                 }
 133         }
 134         current_block.clear();
 135         num_files_in_block = 0;
 136         ++block_num;
 137
 138         if (block_num < blocks_to_keep) {
 139                 keep_current_block = true;
 140                 slot_for_current_block = -1;
 141         } else {
 142                 // Keep every block with equal probability (reservoir sampling).
 143                 uint64_t idx = uniform_int_distribution<uint64_t>(0, block_num)(reservoir_rand);
 144                 keep_current_block = (idx < blocks_to_keep);
 145                 slot_for_current_block = idx;
 146         }
 147 }
 148
 149 string DictionaryBuilder::train(size_t buf_size)
 150 {
 151         string dictionary_buf;
 152         sort(sampled_blocks.begin(), sampled_blocks.end());  // Seemingly important for decompression speed.
 153         for (const string &block : sampled_blocks) {
 154                 dictionary_buf += block;
 155         }
 156
 157         string buf;
 158         buf.resize(buf_size);
 159         size_t ret = ZDICT_trainFromBuffer(&buf[0], buf_size, dictionary_buf.data(), lengths.data(), lengths.size());
 160         if (ZDICT_isError(ret)) {
 161                 return "";
 162         }
 163         dprintf("Sampled %zu bytes in %zu blocks, built a dictionary of size %zu\n", dictionary_buf.size(), lengths.size(), ret);
 164         buf.resize(ret);
 165
 166         sampled_blocks.clear();
 167         lengths.clear();
 168
 169         return buf;
 170 }
 171
 172 class EncodingCorpus : public DatabaseReceiver {
 173 public:
 174         EncodingCorpus(FILE *outfp, size_t block_size, ZSTD_CDict *cdict, bool store_dir_times);
 175         ~EncodingCorpus();
 176
 177         void add_file(std::string filename, dir_time dt) override;
 178         void flush_block() override;
 179         void finish() override;
 180
 181         std::vector<uint64_t> filename_blocks;
 182         size_t num_files = 0, num_files_in_block = 0, num_blocks = 0;
 183         bool seen_trigram(uint32_t trgm)
 184         {
 185                 return invindex[trgm] != nullptr;
 186         }
 187         size_t num_files_seen() const override { return num_files; }
 188         PostingListBuilder &get_pl_builder(uint32_t trgm)
 189         {
 190                 return *invindex[trgm];
 191         }
 192
 193         void add_docid(uint32_t trgm, uint32_t docid)
 194         {
 195                 if (invindex[trgm] == nullptr) {
 196                         invindex[trgm] = new PostingListBuilder;
 197                         invindex[trgm]->add_first_docid(docid);
 198                 } else {
 199                         invindex[trgm]->add_docid(docid);
 200                 }
 201         }
 202
 203         size_t num_trigrams() const;
 204         std::string get_compressed_dir_times();
 205
 206 private:
 207         void compress_dir_times(size_t allowed_slop);
 208
 209         std::unique_ptr<PostingListBuilder *[]> invindex;
 210         FILE *outfp;
 211         std::string current_block;
 212         std::string tempbuf;
 213         const size_t block_size;
 214         const bool store_dir_times;
 215         ZSTD_CDict *cdict;
 216
 217         ZSTD_CStream *dir_time_ctx = nullptr;
 218         std::string dir_times;  // Buffer of still-uncompressed data.
 219         std::string dir_times_compressed;
 220 };
 221
 222
 223 EncodingCorpus::EncodingCorpus(FILE *outfp, size_t block_size, ZSTD_CDict *cdict, bool store_dir_times)
 224         : invindex(new PostingListBuilder *[NUM_TRIGRAMS]), outfp(outfp), block_size(block_size), store_dir_times(store_dir_times), cdict(cdict)
 225 {
 226         fill(invindex.get(), invindex.get() + NUM_TRIGRAMS, nullptr);
 227         if (store_dir_times) {
 228                 dir_time_ctx = ZSTD_createCStream();
 229                 ZSTD_initCStream(dir_time_ctx, /*level=*/6);
 230         }
 231 }
 232
 233 EncodingCorpus::~EncodingCorpus()
 234 {
 235         for (unsigned i = 0; i < NUM_TRIGRAMS; ++i) {
 236                 delete invindex[i];
 237         }
 238 }
 239
 240 void EncodingCorpus::add_file(string filename, dir_time dt)
 241 {
 242         ++num_files;
 243         if (!current_block.empty()) {
 244                 current_block.push_back('\0');
 245         }
 246         current_block += filename;
 247         if (++num_files_in_block == block_size) {
 248                 flush_block();
 249         }
 250
 251         if (store_dir_times) {
 252                 if (dt.sec == -1) {
 253                         // Not a directory.
 254                         dir_times.push_back('\0');
 255                 } else {
 256                         dir_times.push_back('\1');
 257                         dir_times.append(reinterpret_cast<char *>(&dt.sec), sizeof(dt.sec));
 258                         dir_times.append(reinterpret_cast<char *>(&dt.nsec), sizeof(dt.nsec));
 259                 }
 260                 compress_dir_times(/*allowed_slop=*/4096);
 261         }
 262 }
 263
 264 void EncodingCorpus::compress_dir_times(size_t allowed_slop)
 265 {
 266         while (dir_times.size() >= allowed_slop) {
 267                 size_t old_size = dir_times_compressed.size();
 268                 dir_times_compressed.resize(old_size + 4096);
 269
 270                 ZSTD_outBuffer outbuf;
 271                 outbuf.dst = dir_times_compressed.data() + old_size;
 272                 outbuf.size = 4096;
 273                 outbuf.pos = 0;
 274
 275                 ZSTD_inBuffer inbuf;
 276                 inbuf.src = dir_times.data();
 277                 inbuf.size = dir_times.size();
 278                 inbuf.pos = 0;
 279
 280                 int ret = ZSTD_compressStream(dir_time_ctx, &outbuf, &inbuf);
 281                 if (ret < 0) {
 282                         fprintf(stderr, "ZSTD_compressStream() failed\n");
 283                         exit(1);
 284                 }
 285
 286                 dir_times_compressed.resize(old_size + outbuf.pos);
 287                 dir_times.erase(dir_times.begin(), dir_times.begin() + inbuf.pos);
 288
 289                 if (outbuf.pos == 0 && inbuf.pos == 0) {
 290                         // Nothing happened (not enough data?), try again later.
 291                         return;
 292                 }
 293         }
 294 }
 295
 296 void EncodingCorpus::flush_block()
 297 {
 298         if (current_block.empty()) {
 299                 return;
 300         }
 301
 302         uint32_t docid = num_blocks;
 303
 304         // Create trigrams.
 305         const char *ptr = current_block.c_str();
 306         const char *end = ptr + current_block.size();
 307         while (ptr < end - 3) {  // Must be at least one filename left, that's at least three bytes.
 308                 if (ptr[0] == '\0') {
 309                         // This filename is zero bytes, so skip it (and the zero terminator).
 310                         ++ptr;
 311                         continue;
 312                 } else if (ptr[1] == '\0') {
 313                         // This filename is one byte, so skip it (and the zero terminator).
 314                         ptr += 2;
 315                         continue;
 316                 } else if (ptr[2] == '\0') {
 317                         // This filename is two bytes, so skip it (and the zero terminator).
 318                         ptr += 3;
 319                         continue;
 320                 }
 321                 for ( ;; ) {
 322                         // NOTE: Will read one byte past the end of the trigram, but it's OK,
 323                         // since we always call it from contexts where there's a terminating zero byte.
 324                         uint32_t trgm;
 325                         memcpy(&trgm, ptr, sizeof(trgm));
 326                         ++ptr;
 327                         trgm = le32toh(trgm);
 328                         add_docid(trgm & 0xffffff, docid);
 329                         if (trgm <= 0xffffff) {
 330                                 // Terminating zero byte, so we're done with this filename.
 331                                 // Skip the remaining two bytes, and the zero terminator.
 332                                 ptr += 3;
 333                                 break;
 334                         }
 335                 }
 336         }
 337
 338         // Compress and add the filename block.
 339         filename_blocks.push_back(ftell(outfp));
 340         string compressed = zstd_compress(current_block, cdict, &tempbuf);
 341         if (fwrite(compressed.data(), compressed.size(), 1, outfp) != 1) {
 342                 perror("fwrite()");
 343                 exit(1);
 344         }
 345
 346         current_block.clear();
 347         num_files_in_block = 0;
 348         ++num_blocks;
 349 }
 350
 351 void EncodingCorpus::finish()
 352 {
 353         flush_block();
 354 }
 355
 356 size_t EncodingCorpus::num_trigrams() const
 357 {
 358         size_t num = 0;
 359         for (unsigned trgm = 0; trgm < NUM_TRIGRAMS; ++trgm) {
 360                 if (invindex[trgm] != nullptr) {
 361                         ++num;
 362                 }
 363         }
 364         return num;
 365 }
 366
 367 string EncodingCorpus::get_compressed_dir_times()
 368 {
 369         if (!store_dir_times) {
 370                 return "";
 371         }
 372         compress_dir_times(/*allowed_slop=*/0);
 373         assert(dir_times.empty());
 374
 375         for (;;) {
 376                 size_t old_size = dir_times_compressed.size();
 377                 dir_times_compressed.resize(old_size + 4096);
 378
 379                 ZSTD_outBuffer outbuf;
 380                 outbuf.dst = dir_times_compressed.data() + old_size;
 381                 outbuf.size = 4096;
 382                 outbuf.pos = 0;
 383
 384                 int ret = ZSTD_endStream(dir_time_ctx, &outbuf);
 385                 if (ret < 0) {
 386                         fprintf(stderr, "ZSTD_compressStream() failed\n");
 387                         exit(1);
 388                 }
 389
 390                 dir_times_compressed.resize(old_size + outbuf.pos);
 391
 392                 if (ret == 0) {
 393                         // All done.
 394                         break;
 395                 }
 396         }
 397
 398         return dir_times_compressed;
 399 }
 400
 401 string zstd_compress(const string &src, ZSTD_CDict *cdict, string *tempbuf)
 402 {
 403         static ZSTD_CCtx *ctx = nullptr;
 404         if (ctx == nullptr) {
 405                 ctx = ZSTD_createCCtx();
 406         }
 407
 408         size_t max_size = ZSTD_compressBound(src.size());
 409         if (tempbuf->size() < max_size) {
 410                 tempbuf->resize(max_size);
 411         }
 412         size_t size;
 413         if (cdict == nullptr) {
 414                 size = ZSTD_compressCCtx(ctx, &(*tempbuf)[0], max_size, src.data(), src.size(), /*level=*/6);
 415         } else {
 416                 size = ZSTD_compress_usingCDict(ctx, &(*tempbuf)[0], max_size, src.data(), src.size(), cdict);
 417         }
 418         return string(tempbuf->data(), size);
 419 }
 420
 421 bool is_prime(uint32_t x)
 422 {
 423         if ((x % 2) == 0 || (x % 3) == 0) {
 424                 return false;
 425         }
 426         uint32_t limit = ceil(sqrt(x));
 427         for (uint32_t factor = 5; factor <= limit; ++factor) {
 428                 if ((x % factor) == 0) {
 429                         return false;
 430                 }
 431         }
 432         return true;
 433 }
 434
 435 uint32_t next_prime(uint32_t x)
 436 {
 437         if ((x % 2) == 0) {
 438                 ++x;
 439         }
 440         while (!is_prime(x)) {
 441                 x += 2;
 442         }
 443         return x;
 444 }
 445
 446 unique_ptr<Trigram[]> create_hashtable(EncodingCorpus &corpus, const vector<uint32_t> &all_trigrams, uint32_t ht_size, uint32_t num_overflow_slots)
 447 {
 448         unique_ptr<Trigram[]> ht(new Trigram[ht_size + num_overflow_slots + 1]);  // 1 for the sentinel element at the end.
 449         for (unsigned i = 0; i < ht_size + num_overflow_slots + 1; ++i) {
 450                 ht[i].trgm = uint32_t(-1);
 451                 ht[i].num_docids = 0;
 452                 ht[i].offset = 0;
 453         }
 454         for (uint32_t trgm : all_trigrams) {
 455                 // We don't know offset yet, so set it to zero.
 456                 Trigram to_insert{ trgm, uint32_t(corpus.get_pl_builder(trgm).get_num_docids()), 0 };
 457
 458                 uint32_t bucket = hash_trigram(trgm, ht_size);
 459                 unsigned distance = 0;
 460                 while (ht[bucket].num_docids != 0) {
 461                         // Robin Hood hashing; reduces the longest distance by a lot.
 462                         unsigned other_distance = bucket - hash_trigram(ht[bucket].trgm, ht_size);
 463                         if (distance > other_distance) {
 464                                 swap(to_insert, ht[bucket]);
 465                                 distance = other_distance;
 466                         }
 467
 468                         ++bucket, ++distance;
 469                         if (distance > num_overflow_slots) {
 470                                 return nullptr;
 471                         }
 472                 }
 473                 ht[bucket] = to_insert;
 474         }
 475         return ht;
 476 }
 477
 478 DatabaseBuilder::DatabaseBuilder(const char *outfile, gid_t owner, int block_size, string dictionary, bool check_visibility)
 479         : outfile(outfile), block_size(block_size)
 480 {
 481         umask(0027);
 482
 483         string path = outfile;
 484         path.resize(path.find_last_of('/') + 1);
 485         if (path.empty()) {
 486                 path = ".";
 487         }
 488         int fd = -1;
 489 #ifdef O_TMPFILE
 490         fd = open(path.c_str(), O_WRONLY | O_TMPFILE, 0640);
 491         if (fd == -1 && errno != EOPNOTSUPP) {
 492                 perror(path.c_str());
 493                 exit(1);
 494         }
 495 #endif
 496         if (fd == -1) {
 497                 temp_filename = string(outfile) + ".XXXXXX";
 498                 fd = mkstemp(&temp_filename[0]);
 499                 if (fd == -1) {
 500                         perror(temp_filename.c_str());
 501                         exit(1);
 502                 }
 503                 if (fchmod(fd, 0640) == -1) {
 504                         perror("fchmod");
 505                         exit(1);
 506                 }
 507         }
 508
 509         if (owner != (gid_t)-1) {
 510                 if (fchown(fd, (uid_t)-1, owner) == -1) {
 511                         perror("fchown");
 512                         exit(1);
 513                 }
 514         }
 515
 516         outfp = fdopen(fd, "wb");
 517         if (outfp == nullptr) {
 518                 perror(outfile);
 519                 exit(1);
 520         }
 521
 522         // Write the header.
 523         memcpy(hdr.magic, "\0plocate", 8);
 524         hdr.version = -1;  // Mark as broken.
 525         hdr.hashtable_size = 0;  // Not known yet.
 526         hdr.extra_ht_slots = num_overflow_slots;
 527         hdr.num_docids = 0;
 528         hdr.hash_table_offset_bytes = -1;  // We don't know these offsets yet.
 529         hdr.max_version = 2;
 530         hdr.filename_index_offset_bytes = -1;
 531         hdr.zstd_dictionary_length_bytes = -1;
 532         hdr.check_visibility = check_visibility;
 533         fwrite(&hdr, sizeof(hdr), 1, outfp);
 534
 535         if (dictionary.empty()) {
 536                 hdr.zstd_dictionary_offset_bytes = 0;
 537                 hdr.zstd_dictionary_length_bytes = 0;
 538         } else {
 539                 hdr.zstd_dictionary_offset_bytes = ftell(outfp);
 540                 fwrite(dictionary.data(), dictionary.size(), 1, outfp);
 541                 hdr.zstd_dictionary_length_bytes = dictionary.size();
 542                 cdict = ZSTD_createCDict(dictionary.data(), dictionary.size(), /*level=*/6);
 543         }
 544
 545         hdr.directory_data_length_bytes = 0;
 546         hdr.directory_data_offset_bytes = 0;
 547         hdr.next_zstd_dictionary_length_bytes = 0;
 548         hdr.next_zstd_dictionary_offset_bytes = 0;
 549         hdr.conf_block_length_bytes = 0;
 550         hdr.conf_block_offset_bytes = 0;
 551 }
 552
 553 DatabaseReceiver *DatabaseBuilder::start_corpus(bool store_dir_times)
 554 {
 555         corpus_start = steady_clock::now();
 556         corpus = new EncodingCorpus(outfp, block_size, cdict, store_dir_times);
 557         return corpus;
 558 }
 559
 560 void DatabaseBuilder::set_next_dictionary(std::string next_dictionary)
 561 {
 562         this->next_dictionary = move(next_dictionary);
 563 }
 564
 565 void DatabaseBuilder::set_conf_block(std::string conf_block)
 566 {
 567         this->conf_block = move(conf_block);
 568 }
 569
 570 void DatabaseBuilder::finish_corpus()
 571 {
 572         corpus->finish();
 573         hdr.num_docids = corpus->filename_blocks.size();
 574
 575         // Stick an empty block at the end as sentinel.
 576         corpus->filename_blocks.push_back(ftell(outfp));
 577         const size_t bytes_for_filenames = corpus->filename_blocks.back() - corpus->filename_blocks.front();
 578
 579         // Write the offsets to the filenames.
 580         hdr.filename_index_offset_bytes = ftell(outfp);
 581         const size_t bytes_for_filename_index = corpus->filename_blocks.size() * sizeof(uint64_t);
 582         fwrite(corpus->filename_blocks.data(), corpus->filename_blocks.size(), sizeof(uint64_t), outfp);
 583         corpus->filename_blocks.clear();
 584         corpus->filename_blocks.shrink_to_fit();
 585
 586         // Finish up encoding the posting lists.
 587         size_t trigrams = 0, longest_posting_list = 0;
 588         size_t bytes_for_posting_lists = 0;
 589         for (unsigned trgm = 0; trgm < NUM_TRIGRAMS; ++trgm) {
 590                 if (!corpus->seen_trigram(trgm))
 591                         continue;
 592                 PostingListBuilder &pl_builder = corpus->get_pl_builder(trgm);
 593                 pl_builder.finish();
 594                 longest_posting_list = max(longest_posting_list, pl_builder.get_num_docids());
 595                 trigrams += pl_builder.get_num_docids();
 596                 bytes_for_posting_lists += pl_builder.encoded.size();
 597         }
 598         size_t num_trigrams = corpus->num_trigrams();
 599         dprintf("%zu files, %zu different trigrams, %zu entries, avg len %.2f, longest %zu\n",
 600                 corpus->num_files, num_trigrams, trigrams, double(trigrams) / num_trigrams, longest_posting_list);
 601         dprintf("%zu bytes used for posting lists (%.2f bits/entry)\n", bytes_for_posting_lists, 8 * bytes_for_posting_lists / double(trigrams));
 602
 603         dprintf("Building posting lists took %.1f ms.\n\n", 1e3 * duration<float>(steady_clock::now() - corpus_start).count());
 604
 605         // Find the used trigrams.
 606         vector<uint32_t> all_trigrams;
 607         for (unsigned trgm = 0; trgm < NUM_TRIGRAMS; ++trgm) {
 608                 if (corpus->seen_trigram(trgm)) {
 609                         all_trigrams.push_back(trgm);
 610                 }
 611         }
 612
 613         // Create the hash table.
 614         unique_ptr<Trigram[]> hashtable;
 615         uint32_t ht_size = next_prime(all_trigrams.size());
 616         for (;;) {
 617                 hashtable = create_hashtable(*corpus, all_trigrams, ht_size, num_overflow_slots);
 618                 if (hashtable == nullptr) {
 619                         dprintf("Failed creating hash table of size %u, increasing by 5%% and trying again.\n", ht_size);
 620                         ht_size = next_prime(ht_size * 1.05);
 621                 } else {
 622                         dprintf("Created hash table of size %u.\n\n", ht_size);
 623                         break;
 624                 }
 625         }
 626
 627         // Find the offsets for each posting list.
 628         size_t bytes_for_hashtable = (ht_size + num_overflow_slots + 1) * sizeof(Trigram);
 629         uint64_t offset = ftell(outfp) + bytes_for_hashtable;
 630         for (unsigned i = 0; i < ht_size + num_overflow_slots + 1; ++i) {
 631                 hashtable[i].offset = offset;  // Needs to be there even for empty slots.
 632                 if (hashtable[i].num_docids == 0) {
 633                         continue;
 634                 }
 635
 636                 const vector<unsigned char> &encoded = corpus->get_pl_builder(hashtable[i].trgm).encoded;
 637                 offset += encoded.size();
 638         }
 639
 640         // Write the hash table.
 641         hdr.hash_table_offset_bytes = ftell(outfp);
 642         hdr.hashtable_size = ht_size;
 643         fwrite(hashtable.get(), ht_size + num_overflow_slots + 1, sizeof(Trigram), outfp);
 644
 645         // Write the actual posting lists.
 646         for (unsigned i = 0; i < ht_size + num_overflow_slots + 1; ++i) {
 647                 if (hashtable[i].num_docids == 0) {
 648                         continue;
 649                 }
 650                 const vector<unsigned char> &encoded = corpus->get_pl_builder(hashtable[i].trgm).encoded;
 651                 fwrite(encoded.data(), encoded.size(), 1, outfp);
 652         }
 653
 654         // Finally, write the directory times (for updatedb).
 655         string compressed_dir_times = corpus->get_compressed_dir_times();
 656         size_t bytes_for_compressed_dir_times = 0;
 657         if (!compressed_dir_times.empty()) {
 658                 hdr.directory_data_offset_bytes = ftell(outfp);
 659                 hdr.directory_data_length_bytes = compressed_dir_times.size();
 660                 fwrite(compressed_dir_times.data(), compressed_dir_times.size(), 1, outfp);
 661                 bytes_for_compressed_dir_times = compressed_dir_times.size();
 662                 compressed_dir_times.clear();
 663         }
 664
 665         // Write the recommended dictionary for next update.
 666         if (!next_dictionary.empty()) {
 667                 hdr.next_zstd_dictionary_offset_bytes = ftell(outfp);
 668                 hdr.next_zstd_dictionary_length_bytes = next_dictionary.size();
 669                 fwrite(next_dictionary.data(), next_dictionary.size(), 1, outfp);
 670         }
 671
 672         // And the configuration block.
 673         if (!conf_block.empty()) {
 674                 hdr.conf_block_offset_bytes = ftell(outfp);
 675                 hdr.conf_block_length_bytes = conf_block.size();
 676                 fwrite(conf_block.data(), conf_block.size(), 1, outfp);
 677         }
 678
 679         // Rewind, and write the updated header.
 680         hdr.version = 1;
 681         fseek(outfp, 0, SEEK_SET);
 682         fwrite(&hdr, sizeof(hdr), 1, outfp);
 683
 684         if (!temp_filename.empty()) {
 685                 if (rename(temp_filename.c_str(), outfile.c_str()) == -1) {
 686                         perror("rename");
 687                         exit(1);
 688                 }
 689         } else {
 690 #ifdef O_TMPFILE
 691                 // Give the file a proper name, making it visible in the file system.
 692                 // TODO: It would be nice to be able to do this atomically, like with rename.
 693                 unlink(outfile.c_str());
 694                 char procpath[256];
 695                 snprintf(procpath, sizeof(procpath), "/proc/self/fd/%d", fileno(outfp));
 696                 if (linkat(AT_FDCWD, procpath, AT_FDCWD, outfile.c_str(), AT_SYMLINK_FOLLOW) == -1) {
 697                         perror("linkat");
 698                         exit(1);
 699                 }
 700 #endif
 701         }
 702
 703         fclose(outfp);
 704
 705         size_t total_bytes = (bytes_for_hashtable + bytes_for_posting_lists + bytes_for_filename_index + bytes_for_filenames + bytes_for_compressed_dir_times);
 706
 707         dprintf("Block size:     %7d files\n", block_size);
 708         dprintf("Dictionary:     %'7.1f MB\n", hdr.zstd_dictionary_length_bytes / 1048576.0);
 709         dprintf("Hash table:     %'7.1f MB\n", bytes_for_hashtable / 1048576.0);
 710         dprintf("Posting lists:  %'7.1f MB\n", bytes_for_posting_lists / 1048576.0);
 711         dprintf("Filename index: %'7.1f MB\n", bytes_for_filename_index / 1048576.0);
 712         dprintf("Filenames:      %'7.1f MB\n", bytes_for_filenames / 1048576.0);
 713         if (bytes_for_compressed_dir_times != 0) {
 714                 dprintf("Modify times:   %'7.1f MB\n", bytes_for_compressed_dir_times / 1048576.0);
 715         }
 716         dprintf("Total:          %'7.1f MB\n", total_bytes / 1048576.0);
 717         dprintf("\n");
 718 }