3 #include "turbopfor-encode.h"
18 #include <string_view>
25 #define P4NENC_BOUND(n) ((n + 127) / 128 + (n + 32) * sizeof(uint32_t))
27 #define NUM_TRIGRAMS 16777216
30 using namespace std::chrono;
32 string zstd_compress(const string &src, ZSTD_CDict *cdict, string *tempbuf);
34 constexpr unsigned num_overflow_slots = 16;
35 bool use_debug = false;
37 static inline uint32_t read_unigram(const string_view s, size_t idx)
40 return (unsigned char)s[idx];
46 static inline uint32_t read_trigram(const string_view s, size_t start)
48 return read_unigram(s, start) |
49 (read_unigram(s, start + 1) << 8) |
50 (read_unigram(s, start + 2) << 16);
54 DBE_NORMAL = 0, /* A non-directory file */
55 DBE_DIRECTORY = 1, /* A directory */
56 DBE_END = 2 /* End of directory contents; contains no name */
64 uint8_t check_visibility;
75 class PostingListBuilder {
77 inline void add_docid(uint32_t docid);
81 size_t num_docids = 0;
84 void write_header(uint32_t docid);
87 vector<uint32_t> pending_deltas;
89 uint32_t last_block_end, last_docid = -1;
92 void PostingListBuilder::add_docid(uint32_t docid)
94 // Deduplicate against the last inserted value, if any.
95 if (docid == last_docid) {
99 if (num_docids == 0) {
103 last_block_end = last_docid = docid;
107 pending_deltas.push_back(docid - last_docid - 1);
109 if (pending_deltas.size() == 128) {
111 pending_deltas.clear();
112 last_block_end = docid;
117 void PostingListBuilder::finish()
119 if (pending_deltas.empty()) {
123 assert(!encoded.empty()); // write_header() should already have run.
125 // No interleaving for partial blocks.
126 unsigned char buf[P4NENC_BOUND(128)];
127 unsigned char *end = encode_pfor_single_block<128>(pending_deltas.data(), pending_deltas.size(), /*interleaved=*/false, buf);
128 encoded.append(reinterpret_cast<char *>(buf), reinterpret_cast<char *>(end));
131 void PostingListBuilder::append_block()
133 unsigned char buf[P4NENC_BOUND(128)];
134 assert(pending_deltas.size() == 128);
135 unsigned char *end = encode_pfor_single_block<128>(pending_deltas.data(), 128, /*interleaved=*/true, buf);
136 encoded.append(reinterpret_cast<char *>(buf), reinterpret_cast<char *>(end));
139 void PostingListBuilder::write_header(uint32_t docid)
141 unsigned char buf[P4NENC_BOUND(1)];
142 unsigned char *end = write_baseval(docid, buf);
143 encoded.append(reinterpret_cast<char *>(buf), end - buf);
146 class DatabaseReceiver {
148 virtual ~DatabaseReceiver() = default;
149 virtual void add_file(string filename) = 0;
150 virtual void flush_block() = 0;
153 class DictionaryBuilder : public DatabaseReceiver {
155 DictionaryBuilder(size_t blocks_to_keep, size_t block_size)
156 : blocks_to_keep(blocks_to_keep), block_size(block_size) {}
157 void add_file(string filename) override;
158 void flush_block() override;
159 string train(size_t buf_size);
162 const size_t blocks_to_keep, block_size;
163 string current_block;
164 uint64_t block_num = 0;
165 size_t num_files_in_block = 0;
167 std::mt19937 reservoir_rand{ 1234 }; // Fixed seed for reproducibility.
168 bool keep_current_block = true;
169 int64_t slot_for_current_block = -1;
171 vector<string> sampled_blocks;
172 vector<size_t> lengths;
175 void DictionaryBuilder::add_file(string filename)
177 if (keep_current_block) { // Only bother saving the filenames if we're actually keeping the block.
178 if (!current_block.empty()) {
179 current_block.push_back('\0');
181 current_block += filename;
183 if (++num_files_in_block == block_size) {
188 void DictionaryBuilder::flush_block()
190 if (keep_current_block) {
191 if (slot_for_current_block == -1) {
192 lengths.push_back(current_block.size());
193 sampled_blocks.push_back(move(current_block));
195 lengths[slot_for_current_block] = current_block.size();
196 sampled_blocks[slot_for_current_block] = move(current_block);
199 current_block.clear();
200 num_files_in_block = 0;
203 if (block_num < blocks_to_keep) {
204 keep_current_block = true;
205 slot_for_current_block = -1;
207 // Keep every block with equal probability (reservoir sampling).
208 uint64_t idx = uniform_int_distribution<uint64_t>(0, block_num)(reservoir_rand);
209 keep_current_block = (idx < blocks_to_keep);
210 slot_for_current_block = idx;
214 string DictionaryBuilder::train(size_t buf_size)
216 string dictionary_buf;
217 sort(sampled_blocks.begin(), sampled_blocks.end()); // Seemingly important for decompression speed.
218 for (const string &block : sampled_blocks) {
219 dictionary_buf += block;
223 buf.resize(buf_size);
224 size_t ret = ZDICT_trainFromBuffer(&buf[0], buf_size, dictionary_buf.data(), lengths.data(), lengths.size());
225 dprintf("Sampled %zu bytes in %zu blocks, built a dictionary of size %zu\n", dictionary_buf.size(), lengths.size(), ret);
228 sampled_blocks.clear();
234 class Corpus : public DatabaseReceiver {
236 Corpus(FILE *outfp, size_t block_size, ZSTD_CDict *cdict)
237 : invindex(new PostingListBuilder *[NUM_TRIGRAMS]), outfp(outfp), block_size(block_size), cdict(cdict)
239 fill(invindex.get(), invindex.get() + NUM_TRIGRAMS, nullptr);
243 for (unsigned i = 0; i < NUM_TRIGRAMS; ++i) {
248 void add_file(string filename) override;
249 void flush_block() override;
251 vector<uint64_t> filename_blocks;
252 size_t num_files = 0, num_files_in_block = 0, num_blocks = 0;
253 bool seen_trigram(uint32_t trgm)
255 return invindex[trgm] != nullptr;
257 PostingListBuilder &get_pl_builder(uint32_t trgm)
259 if (invindex[trgm] == nullptr) {
260 invindex[trgm] = new PostingListBuilder;
262 return *invindex[trgm];
264 size_t num_trigrams() const;
267 unique_ptr<PostingListBuilder *[]> invindex;
269 string current_block;
271 const size_t block_size;
275 void Corpus::add_file(string filename)
278 if (!current_block.empty()) {
279 current_block.push_back('\0');
281 current_block += filename;
282 if (++num_files_in_block == block_size) {
287 void Corpus::flush_block()
289 if (current_block.empty()) {
293 uint32_t docid = num_blocks;
296 const char *ptr = current_block.c_str();
297 while (ptr < current_block.c_str() + current_block.size()) {
300 for (size_t j = 0; j < s.size() - 2; ++j) {
301 uint32_t trgm = read_trigram(s, j);
302 get_pl_builder(trgm).add_docid(docid);
308 // Compress and add the filename block.
309 filename_blocks.push_back(ftell(outfp));
310 string compressed = zstd_compress(current_block, cdict, &tempbuf);
311 if (fwrite(compressed.data(), compressed.size(), 1, outfp) != 1) {
316 current_block.clear();
317 num_files_in_block = 0;
321 size_t Corpus::num_trigrams() const
324 for (unsigned trgm = 0; trgm < NUM_TRIGRAMS; ++trgm) {
325 if (invindex[trgm] != nullptr) {
332 string read_cstr(FILE *fp)
348 void handle_directory(FILE *fp, DatabaseReceiver *receiver)
351 if (fread(&dummy, sizeof(dummy), 1, fp) != 1) {
359 string dir_path = read_cstr(fp);
360 if (dir_path == "/") {
366 if (type == DBE_NORMAL) {
367 string filename = read_cstr(fp);
368 receiver->add_file(dir_path + "/" + filename);
369 } else if (type == DBE_DIRECTORY) {
370 string dirname = read_cstr(fp);
371 receiver->add_file(dir_path + "/" + dirname);
373 return; // Probably end.
378 void read_mlocate(const char *filename, DatabaseReceiver *receiver)
380 FILE *fp = fopen(filename, "rb");
387 if (fread(&hdr, sizeof(hdr), 1, fp) != 1) {
388 perror("short read");
392 // TODO: Care about the base path.
393 string path = read_cstr(fp);
395 handle_directory(fp, receiver);
400 string zstd_compress(const string &src, ZSTD_CDict *cdict, string *tempbuf)
402 static ZSTD_CCtx *ctx = nullptr;
403 if (ctx == nullptr) {
404 ctx = ZSTD_createCCtx();
407 size_t max_size = ZSTD_compressBound(src.size());
408 if (tempbuf->size() < max_size) {
409 tempbuf->resize(max_size);
412 if (cdict == nullptr) {
413 size = ZSTD_compressCCtx(ctx, &(*tempbuf)[0], max_size, src.data(), src.size(), /*level=*/6);
415 size = ZSTD_compress_usingCDict(ctx, &(*tempbuf)[0], max_size, src.data(), src.size(), cdict);
417 return string(tempbuf->data(), size);
420 bool is_prime(uint32_t x)
422 if ((x % 2) == 0 || (x % 3) == 0) {
425 uint32_t limit = ceil(sqrt(x));
426 for (uint32_t factor = 5; factor <= limit; ++factor) {
427 if ((x % factor) == 0) {
434 uint32_t next_prime(uint32_t x)
439 while (!is_prime(x)) {
445 unique_ptr<Trigram[]> create_hashtable(Corpus &corpus, const vector<uint32_t> &all_trigrams, uint32_t ht_size, uint32_t num_overflow_slots)
447 unique_ptr<Trigram[]> ht(new Trigram[ht_size + num_overflow_slots + 1]); // 1 for the sentinel element at the end.
448 for (unsigned i = 0; i < ht_size + num_overflow_slots + 1; ++i) {
449 ht[i].trgm = uint32_t(-1);
450 ht[i].num_docids = 0;
453 for (uint32_t trgm : all_trigrams) {
454 // We don't know offset yet, so set it to zero.
455 Trigram to_insert{ trgm, uint32_t(corpus.get_pl_builder(trgm).num_docids), 0 };
457 uint32_t bucket = hash_trigram(trgm, ht_size);
458 unsigned distance = 0;
459 while (ht[bucket].num_docids != 0) {
460 // Robin Hood hashing; reduces the longest distance by a lot.
461 unsigned other_distance = bucket - hash_trigram(ht[bucket].trgm, ht_size);
462 if (distance > other_distance) {
463 swap(to_insert, ht[bucket]);
464 distance = other_distance;
467 ++bucket, ++distance;
468 if (distance > num_overflow_slots) {
472 ht[bucket] = to_insert;
477 void do_build(const char *infile, const char *outfile, int block_size)
479 steady_clock::time_point start __attribute__((unused)) = steady_clock::now();
482 FILE *outfp = fopen(outfile, "wb");
486 memcpy(hdr.magic, "\0plocate", 8);
487 hdr.version = -1; // Mark as broken.
488 hdr.hashtable_size = 0; // Not known yet.
489 hdr.extra_ht_slots = num_overflow_slots;
491 hdr.hash_table_offset_bytes = -1; // We don't know these offsets yet.
493 hdr.filename_index_offset_bytes = -1;
494 hdr.zstd_dictionary_length_bytes = -1;
495 fwrite(&hdr, sizeof(hdr), 1, outfp);
497 // Train the dictionary by sampling real blocks.
498 // The documentation for ZDICT_trainFromBuffer() claims that a reasonable
499 // dictionary size is ~100 kB, but 1 kB seems to actually compress better for us,
500 // and decompress just as fast.
501 DictionaryBuilder builder(/*blocks_to_keep=*/1000, block_size);
502 read_mlocate(infile, &builder);
503 string dictionary = builder.train(1024);
504 ZSTD_CDict *cdict = ZSTD_createCDict(dictionary.data(), dictionary.size(), /*level=*/6);
506 hdr.zstd_dictionary_offset_bytes = ftell(outfp);
507 fwrite(dictionary.data(), dictionary.size(), 1, outfp);
508 hdr.zstd_dictionary_length_bytes = dictionary.size();
510 Corpus corpus(outfp, block_size, cdict);
511 read_mlocate(infile, &corpus);
512 if (false) { // To read a plain text file.
513 FILE *fp = fopen(infile, "r");
516 if (fgets(buf, 1024, fp) == nullptr || feof(fp)) {
520 if (s.back() == '\n')
522 corpus.add_file(move(s));
526 corpus.flush_block();
527 dprintf("Read %zu files from %s\n", corpus.num_files, infile);
528 hdr.num_docids = corpus.filename_blocks.size();
530 // Stick an empty block at the end as sentinel.
531 corpus.filename_blocks.push_back(ftell(outfp));
532 const size_t bytes_for_filenames = corpus.filename_blocks.back() - corpus.filename_blocks.front();
534 // Write the offsets to the filenames.
535 hdr.filename_index_offset_bytes = ftell(outfp);
536 const size_t bytes_for_filename_index = corpus.filename_blocks.size() * sizeof(uint64_t);
537 fwrite(corpus.filename_blocks.data(), corpus.filename_blocks.size(), sizeof(uint64_t), outfp);
538 corpus.filename_blocks.clear();
539 corpus.filename_blocks.shrink_to_fit();
541 // Finish up encoding the posting lists.
542 size_t trigrams = 0, longest_posting_list = 0;
543 size_t bytes_for_posting_lists = 0;
544 for (unsigned trgm = 0; trgm < NUM_TRIGRAMS; ++trgm) {
545 if (!corpus.seen_trigram(trgm))
547 PostingListBuilder &pl_builder = corpus.get_pl_builder(trgm);
549 longest_posting_list = max(longest_posting_list, pl_builder.num_docids);
550 trigrams += pl_builder.num_docids;
551 bytes_for_posting_lists += pl_builder.encoded.size();
553 size_t num_trigrams = corpus.num_trigrams();
554 dprintf("%zu files, %zu different trigrams, %zu entries, avg len %.2f, longest %zu\n",
555 corpus.num_files, num_trigrams, trigrams, double(trigrams) / num_trigrams, longest_posting_list);
556 dprintf("%zu bytes used for posting lists (%.2f bits/entry)\n", bytes_for_posting_lists, 8 * bytes_for_posting_lists / double(trigrams));
558 dprintf("Building posting lists took %.1f ms.\n\n", 1e3 * duration<float>(steady_clock::now() - start).count());
560 // Find the used trigrams.
561 vector<uint32_t> all_trigrams;
562 for (unsigned trgm = 0; trgm < NUM_TRIGRAMS; ++trgm) {
563 if (corpus.seen_trigram(trgm)) {
564 all_trigrams.push_back(trgm);
568 // Create the hash table.
569 unique_ptr<Trigram[]> hashtable;
570 uint32_t ht_size = next_prime(all_trigrams.size());
572 hashtable = create_hashtable(corpus, all_trigrams, ht_size, num_overflow_slots);
573 if (hashtable == nullptr) {
574 dprintf("Failed creating hash table of size %u, increasing by 5%% and trying again.\n", ht_size);
575 ht_size = next_prime(ht_size * 1.05);
577 dprintf("Created hash table of size %u.\n\n", ht_size);
582 // Find the offsets for each posting list.
583 size_t bytes_for_hashtable = (ht_size + num_overflow_slots + 1) * sizeof(Trigram);
584 uint64_t offset = ftell(outfp) + bytes_for_hashtable;
585 for (unsigned i = 0; i < ht_size + num_overflow_slots + 1; ++i) {
586 hashtable[i].offset = offset; // Needs to be there even for empty slots.
587 if (hashtable[i].num_docids == 0) {
591 const string &encoded = corpus.get_pl_builder(hashtable[i].trgm).encoded;
592 offset += encoded.size();
595 // Write the hash table.
596 hdr.hash_table_offset_bytes = ftell(outfp);
597 hdr.hashtable_size = ht_size;
598 fwrite(hashtable.get(), ht_size + num_overflow_slots + 1, sizeof(Trigram), outfp);
600 // Write the actual posting lists.
601 for (unsigned i = 0; i < ht_size + num_overflow_slots + 1; ++i) {
602 if (hashtable[i].num_docids == 0) {
605 const string &encoded = corpus.get_pl_builder(hashtable[i].trgm).encoded;
606 fwrite(encoded.data(), encoded.size(), 1, outfp);
609 // Rewind, and write the updated header.
611 fseek(outfp, 0, SEEK_SET);
612 fwrite(&hdr, sizeof(hdr), 1, outfp);
615 size_t total_bytes __attribute__((unused)) = (bytes_for_hashtable + bytes_for_posting_lists + bytes_for_filename_index + bytes_for_filenames);
617 dprintf("Block size: %7d files\n", block_size);
618 dprintf("Dictionary: %'7.1f MB\n", dictionary.size() / 1048576.0);
619 dprintf("Hash table: %'7.1f MB\n", bytes_for_hashtable / 1048576.0);
620 dprintf("Posting lists: %'7.1f MB\n", bytes_for_posting_lists / 1048576.0);
621 dprintf("Filename index: %'7.1f MB\n", bytes_for_filename_index / 1048576.0);
622 dprintf("Filenames: %'7.1f MB\n", bytes_for_filenames / 1048576.0);
623 dprintf("Total: %'7.1f MB\n", total_bytes / 1048576.0);
630 "Usage: plocate-build MLOCATE_DB PLOCATE_DB\n"
632 "Generate plocate index from mlocate.db, typically /var/lib/mlocate/mlocate.db.\n"
633 "Normally, the destination should be /var/lib/mlocate/plocate.db.\n"
635 " -b, --block-size SIZE number of filenames to store in each block (default 32)\n"
636 " --help print this help\n"
637 " --version print version information\n");
642 printf("plocate-build %s\n", PLOCATE_VERSION);
643 printf("Copyright 2020 Steinar H. Gunderson\n");
644 printf("License GPLv2+: GNU GPL version 2 or later <https://gnu.org/licenses/gpl.html>.\n");
645 printf("This is free software: you are free to change and redistribute it.\n");
646 printf("There is NO WARRANTY, to the extent permitted by law.\n");
649 int main(int argc, char **argv)
651 static const struct option long_options[] = {
652 { "block-size", required_argument, 0, 'b' },
653 { "help", no_argument, 0, 'h' },
654 { "version", no_argument, 0, 'V' },
655 { "debug", no_argument, 0, 'D' }, // Not documented.
661 setlocale(LC_ALL, "");
663 int option_index = 0;
664 int c = getopt_long(argc, argv, "b:hVD", long_options, &option_index);
670 block_size = atoi(optarg);
686 if (argc - optind != 2) {
691 do_build(argv[optind], argv[optind + 1], block_size);