4 #include <unordered_map>
11 #include <arpa/inet.h>
13 #include <sys/types.h>
19 #define P4NENC_BOUND(n) ((n+127)/128+(n+32)*sizeof(uint32_t))
21 //#define dprintf(...) fprintf(stderr, __VA_ARGS__);
24 using namespace std::chrono;
26 static inline uint32_t read_unigram(const string &s, size_t idx)
29 return (unsigned char)s[idx];
35 static inline uint32_t read_trigram(const string &s, size_t start)
37 return read_unigram(s, start) |
38 (read_unigram(s, start + 1) << 8) |
39 (read_unigram(s, start + 2) << 16);
44 DBE_NORMAL = 0, /* A non-directory file */
45 DBE_DIRECTORY = 1, /* A directory */
46 DBE_END = 2 /* End of directory contents; contains no name */
55 uint8_t check_visibility;
67 const char *handle_directory(const char *ptr, vector<string> *files)
69 ptr += sizeof(db_directory);
71 string dir_path = ptr;
72 ptr += dir_path.size() + 1;
73 if (dir_path == "/") {
78 uint8_t type = *ptr++;
79 if (type == DBE_NORMAL) {
80 string filename = ptr;
81 files->push_back(dir_path + "/" + filename);
82 ptr += filename.size() + 1;
83 } else if (type == DBE_DIRECTORY) {
85 files->push_back(dir_path + "/" + dirname);
86 ptr += dirname.size() + 1;
93 void read_mlocate(const char *filename, vector<string> *files)
95 int fd = open(filename, O_RDONLY);
100 off_t len = lseek(fd, 0, SEEK_END);
105 const char *data = (char *)mmap(nullptr, len, PROT_READ, MAP_SHARED, fd, /*offset=*/0);
106 if (data == MAP_FAILED) {
111 const db_header *hdr = (const db_header *)data;
113 // TODO: Care about the base path.
114 string path = data + sizeof(db_header);
115 uint64_t offset = sizeof(db_header) + path.size() + 1 + ntohl(hdr->conf_size);
117 const char *ptr = data + offset;
118 while (ptr < data + len) {
119 ptr = handle_directory(ptr, files);
122 munmap((void *)data, len);
126 string zstd_compress(const string &src)
128 size_t max_size = ZSTD_compressBound(src.size());
130 dst.resize(max_size);
131 size_t size = ZSTD_compress(&dst[0], max_size, src.data(), src.size(), /*level=*/6);
136 void do_build(const char *infile, const char *outfile, int block_size)
138 //steady_clock::time_point start = steady_clock::now();
140 vector<string> files;
141 read_mlocate(infile, &files);
142 if (false) { // To read a plain text file.
143 FILE *fp = fopen(infile, "r");
146 if (fgets(buf, 1024, fp) == nullptr || feof(fp)) {
150 if (s.back() == '\n') s.pop_back();
151 files.push_back(move(s));
155 dprintf("Read %zu files from %s\n", files.size(), infile);
157 unordered_map<uint32_t, string> pl;
158 size_t trigrams = 0, longest_posting_list = 0;
159 unordered_map<uint32_t, vector<uint32_t>> invindex;
160 for (size_t i = 0; i < files.size(); ++i) {
161 uint32_t docid = i / block_size;
162 const string &s = files[i];
164 for (size_t j = 0; j < s.size() - 2; ++j) {
165 uint32_t trgm = read_trigram(s, j);
166 vector<uint32_t> &docids = invindex[trgm];
167 if (docids.empty() || docids.back() != docid) {
168 docids.push_back(docid);
174 size_t bytes_used = 0;
175 for (auto &[trigram, docids] : invindex) {
176 longest_posting_list = max(longest_posting_list, docids.size());
177 trigrams += docids.size();
179 size_t bytes_needed = P4NENC_BOUND(docids.size());
180 if (buf.size() < bytes_needed) buf.resize(bytes_needed);
181 size_t bytes = p4nd1enc128v32(&docids[0], docids.size(), reinterpret_cast<unsigned char *>(&buf[0]));
182 pl[trigram] = string(buf.data(), bytes);
185 dprintf("%zu files, %zu different trigrams, %zu entries, avg len %.2f, longest %zu\n",
186 files.size(), invindex.size(), trigrams, double(trigrams) / invindex.size(), longest_posting_list);
188 dprintf("%zu bytes used for posting lists (%.2f bits/entry)\n", bytes_used, 8 * bytes_used / double(trigrams));
189 //steady_clock::time_point end = steady_clock::now();
190 dprintf("Building posting lists took %.1f ms.\n\n", 1e3 * duration<float>(end - start).count());
192 vector<uint32_t> all_trigrams;
193 for (auto &[trigram, docids] : invindex) {
194 all_trigrams.push_back(trigram);
196 sort(all_trigrams.begin(), all_trigrams.end());
199 FILE *outfp = fopen(outfile, "wb");
202 uint64_t num_trigrams = invindex.size(); // 64 to get alignment.
203 fwrite(&num_trigrams, sizeof(num_trigrams), 1, outfp);
205 // Find out where the posting lists will end.
206 uint64_t offset = sizeof(uint64_t) * 2 + 16 * all_trigrams.size();
207 uint64_t filename_index_offset = offset;
208 for (uint32_t trgm : all_trigrams) {
209 filename_index_offset += pl[trgm].size();
211 fwrite(&filename_index_offset, sizeof(filename_index_offset), 1, outfp);
213 size_t bytes_for_trigrams = 0, bytes_for_posting_lists = 0, bytes_for_filename_index = 0, bytes_for_filenames = 0;
215 for (uint32_t trgm : all_trigrams) {
216 // 16 bytes: trgm (4), number of docids (4), byte offset (8)
217 fwrite(&trgm, sizeof(trgm), 1, outfp); // One byte wasted, but OK.
218 uint32_t num_docids = invindex[trgm].size();
219 fwrite(&num_docids, sizeof(num_docids), 1, outfp);
220 fwrite(&offset, sizeof(offset), 1, outfp);
221 offset += pl[trgm].size();
222 bytes_for_trigrams += 16;
225 // Write the actual posting lists.
226 for (uint32_t trgm : all_trigrams) {
227 fwrite(pl[trgm].data(), pl[trgm].size(), 1, outfp);
228 bytes_for_posting_lists += pl[trgm].size();
231 // Compress the filenames into blocks.
232 vector<string> filename_blocks;
233 string uncompressed_filenames;
234 int num_files_this_block = 0;
238 for (string &filename : files) {
239 uncompressed_filenames += filename;
241 if (++num_files_this_block == block_size) {
242 filename_blocks.push_back(zstd_compress(uncompressed_filenames));
243 uncompressed_filenames.clear();
244 num_files_this_block = 0;
246 uncompressed_filenames.push_back('\0');
249 if (num_files_this_block > 0) {
250 filename_blocks.push_back(zstd_compress(uncompressed_filenames));
254 // Stick an empty block at the end as sentinel.
255 filename_blocks.push_back("");
257 // Write the offsets to the filenames.
258 offset = filename_index_offset + filename_blocks.size() * sizeof(offset);
259 for (const string &filename : filename_blocks) {
260 fwrite(&offset, sizeof(offset), 1, outfp);
261 offset += filename.size();
262 bytes_for_filename_index += sizeof(offset);
263 bytes_for_filenames += filename.size();
266 // Write the actual filenames.
267 for (const string &filename : filename_blocks) {
268 fwrite(filename.data(), filename.size(), 1, outfp);
273 //size_t total_bytes = (bytes_for_trigrams + bytes_for_posting_lists + bytes_for_filename_index + bytes_for_filenames);
275 dprintf("Block size: %7d files\n", block_size);
276 dprintf("Trigrams: %'7.1f MB\n", bytes_for_trigrams / 1048576.0);
277 dprintf("Posting lists: %'7.1f MB\n", bytes_for_posting_lists / 1048576.0);
278 dprintf("Filename index: %'7.1f MB\n", bytes_for_filename_index / 1048576.0);
279 dprintf("Filenames: %'7.1f MB\n", bytes_for_filenames / 1048576.0);
280 dprintf("Total: %'7.1f MB\n", total_bytes / 1048576.0);
284 int main(int argc, char **argv)
286 do_build(argv[1], argv[2], 32);