git.sesse.net Git - plocate/blob - plocate-build.cpp

   1 #include "db.h"
   2 #include "vp4.h"
   3
   4 #include <algorithm>
   5 #include <arpa/inet.h>
   6 #include <assert.h>
   7 #include <chrono>
   8 #include <endian.h>
   9 #include <fcntl.h>
  10 #include <math.h>
  11 #include <memory>
  12 #include <stdio.h>
  13 #include <string.h>
  14 #include <string>
  15 #include <sys/stat.h>
  16 #include <sys/types.h>
  17 #include <unistd.h>
  18 #include <unordered_map>
  19 #include <vector>
  20 #include <zstd.h>
  21
  22 #define P4NENC_BOUND(n) ((n + 127) / 128 + (n + 32) * sizeof(uint32_t))
  23 #define dprintf(...)
  24 //#define dprintf(...) fprintf(stderr, __VA_ARGS__);
  25
  26 #define NUM_TRIGRAMS 16777216
  27
  28 using namespace std;
  29 using namespace std::chrono;
  30
  31 string zstd_compress(const string &src, string *tempbuf);
  32
  33 constexpr unsigned num_overflow_slots = 16;
  34
  35 static inline uint32_t read_unigram(const string_view s, size_t idx)
  36 {
  37         if (idx < s.size()) {
  38                 return (unsigned char)s[idx];
  39         } else {
  40                 return 0;
  41         }
  42 }
  43
  44 static inline uint32_t read_trigram(const string_view s, size_t start)
  45 {
  46         return read_unigram(s, start) |
  47                 (read_unigram(s, start + 1) << 8) |
  48                 (read_unigram(s, start + 2) << 16);
  49 }
  50
  51 enum {
  52         DBE_NORMAL = 0, /* A non-directory file */
  53         DBE_DIRECTORY = 1, /* A directory */
  54         DBE_END = 2 /* End of directory contents; contains no name */
  55 };
  56
  57 // From mlocate.
  58 struct db_header {
  59         uint8_t magic[8];
  60         uint32_t conf_size;
  61         uint8_t version;
  62         uint8_t check_visibility;
  63         uint8_t pad[2];
  64 };
  65
  66 // From mlocate.
  67 struct db_directory {
  68         uint64_t time_sec;
  69         uint32_t time_nsec;
  70         uint8_t pad[4];
  71 };
  72
  73 class PostingListBuilder {
  74 public:
  75         inline void add_docid(uint32_t docid);
  76         void finish();
  77
  78         string encoded;
  79         size_t num_docids = 0;
  80
  81 private:
  82         void write_header(uint32_t docid);
  83         void append_block();
  84
  85         vector<uint32_t> pending_docids;
  86
  87         uint32_t last_block_end, last_docid = -1;
  88 };
  89
  90 void PostingListBuilder::add_docid(uint32_t docid)
  91 {
  92         // Deduplicate against the last inserted value, if any.
  93         if (docid == last_docid) {
  94                 return;
  95         }
  96
  97         if (num_docids == 0) {
  98                 // Very first docid.
  99                 write_header(docid);
 100                 ++num_docids;
 101                 last_block_end = last_docid = docid;
 102                 return;
 103         }
 104
 105         last_docid = docid;
 106         pending_docids.push_back(docid);
 107         if (pending_docids.size() == 128) {
 108                 append_block();
 109                 pending_docids.clear();
 110                 last_block_end = docid;
 111         }
 112         ++num_docids;
 113 }
 114
 115 void PostingListBuilder::finish()
 116 {
 117         if (pending_docids.empty()) {
 118                 return;
 119         }
 120
 121         assert(!encoded.empty());  // write_header() should already have run.
 122
 123         // No interleaving for partial blocks.
 124         unsigned char buf[P4NENC_BOUND(128)];
 125         unsigned char *end = p4d1enc32(pending_docids.data(), pending_docids.size(), buf, last_block_end);
 126         encoded.append(reinterpret_cast<char *>(buf), reinterpret_cast<char *>(end));
 127 }
 128
 129 void PostingListBuilder::append_block()
 130 {
 131         unsigned char buf[P4NENC_BOUND(128)];
 132         assert(pending_docids.size() == 128);
 133         unsigned char *end = p4d1enc32(pending_docids.data(), 128, buf, last_block_end);
 134         encoded.append(reinterpret_cast<char *>(buf), reinterpret_cast<char *>(end));
 135 }
 136
 137 void PostingListBuilder::write_header(uint32_t docid)
 138 {
 139         unsigned char buf[P4NENC_BOUND(1)];
 140         size_t bytes = p4nd1enc32(&docid, 1, buf);
 141         encoded.append(reinterpret_cast<char *>(buf), bytes);
 142 }
 143
 144 class Corpus {
 145 public:
 146         Corpus(FILE *outfp, size_t block_size)
 147                 : invindex(new PostingListBuilder*[NUM_TRIGRAMS]), outfp(outfp), block_size(block_size) {}
 148         void add_file(string filename);
 149         void flush_block();
 150
 151         vector<uint64_t> filename_blocks;
 152         size_t num_files = 0, num_files_in_block = 0, num_blocks = 0;
 153         bool seen_trigram(uint32_t trgm) {
 154                 return invindex[trgm] != nullptr;
 155         }
 156         PostingListBuilder& get_pl_builder(uint32_t trgm) {
 157                 if (invindex[trgm] == nullptr) {
 158                         invindex[trgm] = new PostingListBuilder;
 159                 }
 160                 return *invindex[trgm];
 161         }
 162
 163 private:
 164         unique_ptr<PostingListBuilder*[]> invindex;
 165         FILE *outfp;
 166         string current_block;
 167         string tempbuf;
 168         const size_t block_size;
 169 };
 170
 171 void Corpus::add_file(string filename)
 172 {
 173         ++num_files;
 174         if (!current_block.empty()) {
 175                 current_block.push_back('\0');
 176         }
 177         current_block += filename;
 178         if (++num_files_in_block == block_size) {
 179                 flush_block();
 180         }
 181 }
 182
 183 void Corpus::flush_block()
 184 {
 185         if (current_block.empty()) {
 186                 return;
 187         }
 188
 189         uint32_t docid = num_blocks;
 190
 191         // Create trigrams.
 192         const char *ptr = current_block.c_str();
 193         while (ptr < current_block.c_str() + current_block.size()) {
 194                 string_view s(ptr);
 195                 if (s.size() >= 3) {
 196                         for (size_t j = 0; j < s.size() - 2; ++j) {
 197                                 uint32_t trgm = read_trigram(s, j);
 198                                 get_pl_builder(trgm).add_docid(docid);
 199                         }
 200                 }
 201                 ptr += s.size() + 1;
 202         }
 203
 204         // Compress and add the filename block.
 205         filename_blocks.push_back(ftell(outfp));
 206         string compressed = zstd_compress(current_block, &tempbuf);
 207         if (fwrite(compressed.data(), compressed.size(), 1, outfp) != 1) {
 208                 perror("fwrite()");
 209                 exit(1);
 210         }
 211
 212         current_block.clear();
 213         num_files_in_block = 0;
 214         ++num_blocks;
 215 }
 216
 217 string read_cstr(FILE *fp)
 218 {
 219         string ret;
 220         for ( ;; ) {
 221                 int ch = getc(fp);
 222                 if (ch == -1) {
 223                         perror("getc");
 224                         exit(1);
 225                 }
 226                 if (ch == 0) {
 227                         return ret;
 228                 }
 229                 ret.push_back(ch);
 230         }
 231 }
 232
 233 void handle_directory(FILE *fp, Corpus *corpus)
 234 {
 235         db_directory dummy;
 236         if (fread(&dummy, sizeof(dummy), 1, fp) != 1) {
 237                 if (feof(fp)) {
 238                         return;
 239                 } else {
 240                         perror("fread");
 241                 }
 242         }
 243
 244         string dir_path = read_cstr(fp);
 245         if (dir_path == "/") {
 246                 dir_path = "";
 247         }
 248
 249         for (;;) {
 250                 int type = getc(fp);
 251                 if (type == DBE_NORMAL) {
 252                         string filename = read_cstr(fp);
 253                         corpus->add_file(dir_path + "/" + filename);
 254                 } else if (type == DBE_DIRECTORY) {
 255                         string dirname = read_cstr(fp);
 256                         corpus->add_file(dir_path + "/" + dirname);
 257                 } else {
 258                         return;  // Probably end.
 259                 }
 260         }
 261 }
 262
 263 void read_mlocate(const char *filename, Corpus *corpus)
 264 {
 265         FILE *fp = fopen(filename, "rb");
 266         if (fp == nullptr) {
 267                 perror(filename);
 268                 exit(1);
 269         }
 270
 271         db_header hdr;
 272         if (fread(&hdr, sizeof(hdr), 1, fp) != 1) {
 273                 perror("short read");
 274                 exit(1);
 275         }
 276
 277         // TODO: Care about the base path.
 278         string path = read_cstr(fp);
 279         while (!feof(fp)) {
 280                 handle_directory(fp, corpus);
 281         }
 282         fclose(fp);
 283 }
 284
 285 string zstd_compress(const string &src, string *tempbuf)
 286 {
 287         size_t max_size = ZSTD_compressBound(src.size());
 288         if (tempbuf->size() < max_size) {
 289                 tempbuf->resize(max_size);
 290         }
 291         size_t size = ZSTD_compress(&(*tempbuf)[0], max_size, src.data(), src.size(), /*level=*/6);
 292         return string(tempbuf->data(), size);
 293 }
 294
 295 bool is_prime(uint32_t x)
 296 {
 297         if ((x % 2) == 0 || (x % 3) == 0) {
 298                 return false;
 299         }
 300         uint32_t limit = ceil(sqrt(x));
 301         for (uint32_t factor = 5; factor <= limit; ++factor) {
 302                 if ((x % factor) == 0) {
 303                         return false;
 304                 }
 305         }
 306         return true;
 307 }
 308
 309 uint32_t next_prime(uint32_t x)
 310 {
 311         if ((x % 2) == 0) {
 312                 ++x;
 313         }
 314         while (!is_prime(x)) {
 315                 x += 2;
 316         }
 317         return x;
 318 }
 319
 320 unique_ptr<Trigram[]> create_hashtable(Corpus &corpus, const vector<uint32_t> &all_trigrams, uint32_t ht_size, uint32_t num_overflow_slots)
 321 {
 322         unique_ptr<Trigram[]> ht(new Trigram[ht_size + num_overflow_slots + 1]);  // 1 for the sentinel element at the end.
 323         for (unsigned i = 0; i < ht_size + num_overflow_slots + 1; ++i) {
 324                 ht[i].trgm = uint32_t(-1);
 325                 ht[i].num_docids = 0;
 326                 ht[i].offset = 0;
 327         }
 328         for (uint32_t trgm : all_trigrams) {
 329                 // We don't know offset yet, so set it to zero.
 330                 Trigram to_insert{ trgm, uint32_t(corpus.get_pl_builder(trgm).num_docids), 0 };
 331
 332                 uint32_t bucket = hash_trigram(trgm, ht_size);
 333                 unsigned distance = 0;
 334                 while (ht[bucket].num_docids != 0) {
 335                         // Robin Hood hashing; reduces the longest distance by a lot.
 336                         unsigned other_distance = bucket - hash_trigram(ht[bucket].trgm, ht_size);
 337                         if (distance > other_distance) {
 338                                 swap(to_insert, ht[bucket]);
 339                                 distance = other_distance;
 340                         }
 341
 342                         ++bucket, ++distance;
 343                         if (distance > num_overflow_slots) {
 344                                 return nullptr;
 345                         }
 346                 }
 347                 ht[bucket] = to_insert;
 348         }
 349         return ht;
 350 }
 351
 352 void do_build(const char *infile, const char *outfile, int block_size)
 353 {
 354         steady_clock::time_point start __attribute__((unused)) = steady_clock::now();
 355
 356         umask(0027);
 357         FILE *outfp = fopen(outfile, "wb");
 358
 359         // Write the header.
 360         Header hdr;
 361         memcpy(hdr.magic, "\0plocate", 8);
 362         hdr.version = -1;  // Mark as broken.
 363         hdr.hashtable_size = 0;  // Not known yet.
 364         hdr.extra_ht_slots = num_overflow_slots;
 365         hdr.hash_table_offset_bytes = -1;  // We don't know these offsets yet.
 366         hdr.filename_index_offset_bytes = -1;
 367         fwrite(&hdr, sizeof(hdr), 1, outfp);
 368
 369         Corpus corpus(outfp, block_size);
 370
 371         read_mlocate(infile, &corpus);
 372         if (false) {  // To read a plain text file.
 373                 FILE *fp = fopen(infile, "r");
 374                 while (!feof(fp)) {
 375                         char buf[1024];
 376                         if (fgets(buf, 1024, fp) == nullptr || feof(fp)) {
 377                                 break;
 378                         }
 379                         string s(buf);
 380                         if (s.back() == '\n')
 381                                 s.pop_back();
 382                         corpus.add_file(move(s));
 383                 }
 384                 fclose(fp);
 385         }
 386         corpus.flush_block();
 387         dprintf("Read %zu files from %s\n", corpus.num_files, infile);
 388         hdr.num_docids = corpus.filename_blocks.size();
 389
 390         // Stick an empty block at the end as sentinel.
 391         corpus.filename_blocks.push_back(ftell(outfp));
 392         const size_t bytes_for_filenames = corpus.filename_blocks.back() - corpus.filename_blocks.front();
 393
 394         // Write the offsets to the filenames.
 395         hdr.filename_index_offset_bytes = ftell(outfp);
 396         const size_t bytes_for_filename_index = corpus.filename_blocks.size() * sizeof(uint64_t);
 397         fwrite(corpus.filename_blocks.data(), corpus.filename_blocks.size(), sizeof(uint64_t), outfp);
 398         corpus.filename_blocks.clear();
 399         corpus.filename_blocks.shrink_to_fit();
 400
 401         // Finish up encoding the posting lists.
 402         size_t trigrams = 0, longest_posting_list = 0;
 403         size_t bytes_for_posting_lists = 0;
 404         for (unsigned trgm = 0; trgm < NUM_TRIGRAMS; ++trgm) {
 405                 if (!corpus.seen_trigram(trgm)) continue;
 406                 PostingListBuilder &pl_builder = corpus.get_pl_builder(trgm);
 407                 pl_builder.finish();
 408                 longest_posting_list = max(longest_posting_list, pl_builder.num_docids);
 409                 trigrams += pl_builder.num_docids;
 410                 bytes_for_posting_lists += pl_builder.encoded.size();
 411         }
 412         dprintf("%zu files, %zu different trigrams, %zu entries, avg len %.2f, longest %zu\n",
 413                 corpus.num_files, corpus.invindex.size(), trigrams, double(trigrams) / corpus.invindex.size(), longest_posting_list);
 414         dprintf("%zu bytes used for posting lists (%.2f bits/entry)\n", bytes_for_posting_lists, 8 * bytes_for_posting_lists / double(trigrams));
 415
 416         dprintf("Building posting lists took %.1f ms.\n\n", 1e3 * duration<float>(steady_clock::now() - start).count());
 417
 418         // Find the used trigrams.
 419         vector<uint32_t> all_trigrams;
 420         for (unsigned trgm = 0; trgm < NUM_TRIGRAMS; ++trgm) {
 421                 if (corpus.seen_trigram(trgm)) {
 422                         all_trigrams.push_back(trgm);
 423                 }
 424         }
 425
 426         // Create the hash table.
 427         unique_ptr<Trigram[]> hashtable;
 428         uint32_t ht_size = next_prime(all_trigrams.size());
 429         for (;;) {
 430                 hashtable = create_hashtable(corpus, all_trigrams, ht_size, num_overflow_slots);
 431                 if (hashtable == nullptr) {
 432                         dprintf("Failed creating hash table of size %u, increasing by 5%% and trying again.\n", ht_size);
 433                         ht_size = next_prime(ht_size * 1.05);
 434                 } else {
 435                         dprintf("Created hash table of size %u.\n\n", ht_size);
 436                         break;
 437                 }
 438         }
 439
 440         // Find the offsets for each posting list.
 441         size_t bytes_for_hashtable = (ht_size + num_overflow_slots + 1) * sizeof(Trigram);
 442         uint64_t offset = ftell(outfp) + bytes_for_hashtable;
 443         for (unsigned i = 0; i < ht_size + num_overflow_slots + 1; ++i) {
 444                 hashtable[i].offset = offset;  // Needs to be there even for empty slots.
 445                 if (hashtable[i].num_docids == 0) {
 446                         continue;
 447                 }
 448
 449                 const string &encoded = corpus.get_pl_builder(hashtable[i].trgm).encoded;
 450                 offset += encoded.size();
 451         }
 452
 453         // Write the hash table.
 454         hdr.hash_table_offset_bytes = ftell(outfp);
 455         hdr.hashtable_size = ht_size;
 456         fwrite(hashtable.get(), ht_size + num_overflow_slots + 1, sizeof(Trigram), outfp);
 457
 458         // Write the actual posting lists.
 459         for (unsigned i = 0; i < ht_size + num_overflow_slots + 1; ++i) {
 460                 if (hashtable[i].num_docids == 0) {
 461                         continue;
 462                 }
 463                 const string &encoded = corpus.get_pl_builder(hashtable[i].trgm).encoded;
 464                 fwrite(encoded.data(), encoded.size(), 1, outfp);
 465         }
 466
 467         // Rewind, and write the updated header.
 468         hdr.version = 0;
 469         fseek(outfp, 0, SEEK_SET);
 470         fwrite(&hdr, sizeof(hdr), 1, outfp);
 471         fclose(outfp);
 472
 473         size_t total_bytes __attribute__((unused)) = (bytes_for_hashtable + bytes_for_posting_lists + bytes_for_filename_index + bytes_for_filenames);
 474
 475         dprintf("Block size:     %7d files\n", block_size);
 476         dprintf("Hash table:     %'7.1f MB\n", bytes_for_hashtable / 1048576.0);
 477         dprintf("Posting lists:  %'7.1f MB\n", bytes_for_posting_lists / 1048576.0);
 478         dprintf("Filename index: %'7.1f MB\n", bytes_for_filename_index / 1048576.0);
 479         dprintf("Filenames:      %'7.1f MB\n", bytes_for_filenames / 1048576.0);
 480         dprintf("Total:          %'7.1f MB\n", total_bytes / 1048576.0);
 481         dprintf("\n");
 482 }
 483
 484 int main(int argc, char **argv)
 485 {
 486         do_build(argv[1], argv[2], 32);
 487         exit(EXIT_SUCCESS);
 488 }