#include <iosfwd>
#include <math.h>
#include <memory>
+#include <random>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <utility>
#include <vector>
+#include <zdict.h>
#include <zstd.h>
#define P4NENC_BOUND(n) ((n + 127) / 128 + (n + 32) * sizeof(uint32_t))
using namespace std;
using namespace std::chrono;
-string zstd_compress(const string &src, string *tempbuf);
+string zstd_compress(const string &src, ZSTD_CDict *cdict, string *tempbuf);
constexpr unsigned num_overflow_slots = 16;
encoded.append(reinterpret_cast<char *>(buf), end - buf);
}
-class Corpus {
+class DatabaseReceiver {
public:
- Corpus(FILE *outfp, size_t block_size)
- : invindex(new PostingListBuilder *[NUM_TRIGRAMS]), outfp(outfp), block_size(block_size)
+ virtual ~DatabaseReceiver() = default;
+ virtual void add_file(string filename) = 0;
+ virtual void flush_block() = 0;
+};
+
+class DictionaryBuilder : public DatabaseReceiver {
+public:
+ DictionaryBuilder(size_t blocks_to_keep, size_t block_size)
+ : blocks_to_keep(blocks_to_keep), block_size(block_size) {}
+ void add_file(string filename) override;
+ void flush_block() override;
+ string train(size_t buf_size);
+
+private:
+ const size_t blocks_to_keep, block_size;
+ string current_block;
+ uint64_t block_num = 0;
+ size_t num_files_in_block = 0;
+
+ std::mt19937 reservoir_rand{ 1234 }; // Fixed seed for reproducibility.
+ bool keep_current_block = true;
+ int64_t slot_for_current_block = -1;
+
+ vector<string> sampled_blocks;
+ vector<size_t> lengths;
+};
+
+void DictionaryBuilder::add_file(string filename)
+{
+ if (keep_current_block) { // Only bother saving the filenames if we're actually keeping the block.
+ if (!current_block.empty()) {
+ current_block.push_back('\0');
+ }
+ current_block += filename;
+ }
+ if (++num_files_in_block == block_size) {
+ flush_block();
+ }
+}
+
+void DictionaryBuilder::flush_block()
+{
+ if (keep_current_block) {
+ if (slot_for_current_block == -1) {
+ lengths.push_back(current_block.size());
+ sampled_blocks.push_back(move(current_block));
+ } else {
+ lengths[slot_for_current_block] = current_block.size();
+ sampled_blocks[slot_for_current_block] = move(current_block);
+ }
+ }
+ current_block.clear();
+ num_files_in_block = 0;
+ ++block_num;
+
+ if (block_num < blocks_to_keep) {
+ keep_current_block = true;
+ slot_for_current_block = -1;
+ } else {
+ // Keep every block with equal probability (reservoir sampling).
+ uint64_t idx = uniform_int_distribution<uint64_t>(0, block_num)(reservoir_rand);
+ keep_current_block = (idx < blocks_to_keep);
+ slot_for_current_block = idx;
+ }
+}
+
+string DictionaryBuilder::train(size_t buf_size)
+{
+ string dictionary_buf;
+ sort(sampled_blocks.begin(), sampled_blocks.end()); // Seemingly important for decompression speed.
+ for (const string &block : sampled_blocks) {
+ dictionary_buf += block;
+ }
+
+ string buf;
+ buf.resize(buf_size);
+ size_t ret = ZDICT_trainFromBuffer(&buf[0], buf_size, dictionary_buf.data(), lengths.data(), lengths.size());
+ dprintf(stderr, "Sampled %zu bytes in %zu blocks, built a dictionary of size %zu\n", dictionary_buf.size(), lengths.size(), ret);
+ buf.resize(ret);
+
+ sampled_blocks.clear();
+ lengths.clear();
+
+ return buf;
+}
+
+class Corpus : public DatabaseReceiver {
+public:
+ Corpus(FILE *outfp, size_t block_size, ZSTD_CDict *cdict)
+ : invindex(new PostingListBuilder *[NUM_TRIGRAMS]), outfp(outfp), block_size(block_size), cdict(cdict)
{
fill(invindex.get(), invindex.get() + NUM_TRIGRAMS, nullptr);
}
- ~Corpus()
+ ~Corpus() override
{
for (unsigned i = 0; i < NUM_TRIGRAMS; ++i) {
delete invindex[i];
}
}
- void add_file(string filename);
- void flush_block();
+ void add_file(string filename) override;
+ void flush_block() override;
vector<uint64_t> filename_blocks;
size_t num_files = 0, num_files_in_block = 0, num_blocks = 0;
string current_block;
string tempbuf;
const size_t block_size;
+ ZSTD_CDict *cdict;
};
void Corpus::add_file(string filename)
// Compress and add the filename block.
filename_blocks.push_back(ftell(outfp));
- string compressed = zstd_compress(current_block, &tempbuf);
+ string compressed = zstd_compress(current_block, cdict, &tempbuf);
if (fwrite(compressed.data(), compressed.size(), 1, outfp) != 1) {
perror("fwrite()");
exit(1);
}
}
-void handle_directory(FILE *fp, Corpus *corpus)
+void handle_directory(FILE *fp, DatabaseReceiver *receiver)
{
db_directory dummy;
if (fread(&dummy, sizeof(dummy), 1, fp) != 1) {
int type = getc(fp);
if (type == DBE_NORMAL) {
string filename = read_cstr(fp);
- corpus->add_file(dir_path + "/" + filename);
+ receiver->add_file(dir_path + "/" + filename);
} else if (type == DBE_DIRECTORY) {
string dirname = read_cstr(fp);
- corpus->add_file(dir_path + "/" + dirname);
+ receiver->add_file(dir_path + "/" + dirname);
} else {
return; // Probably end.
}
}
}
-void read_mlocate(const char *filename, Corpus *corpus)
+void read_mlocate(const char *filename, DatabaseReceiver *receiver)
{
FILE *fp = fopen(filename, "rb");
if (fp == nullptr) {
// TODO: Care about the base path.
string path = read_cstr(fp);
while (!feof(fp)) {
- handle_directory(fp, corpus);
+ handle_directory(fp, receiver);
}
fclose(fp);
}
-string zstd_compress(const string &src, string *tempbuf)
+string zstd_compress(const string &src, ZSTD_CDict *cdict, string *tempbuf)
{
+ static ZSTD_CCtx *ctx = nullptr;
+ if (ctx == nullptr) {
+ ctx = ZSTD_createCCtx();
+ }
+
size_t max_size = ZSTD_compressBound(src.size());
if (tempbuf->size() < max_size) {
tempbuf->resize(max_size);
}
- static ZSTD_CCtx *ctx = ZSTD_createCCtx(); // Reused across calls.
- size_t size = ZSTD_compressCCtx(ctx, &(*tempbuf)[0], max_size, src.data(), src.size(), /*level=*/6);
+ size_t size;
+ if (cdict == nullptr) {
+ size = ZSTD_compressCCtx(ctx, &(*tempbuf)[0], max_size, src.data(), src.size(), /*level=*/6);
+ } else {
+ size = ZSTD_compress_usingCDict(ctx, &(*tempbuf)[0], max_size, src.data(), src.size(), cdict);
+ }
return string(tempbuf->data(), size);
}
hdr.extra_ht_slots = num_overflow_slots;
hdr.num_docids = 0;
hdr.hash_table_offset_bytes = -1; // We don't know these offsets yet.
+ hdr.max_version = 1;
hdr.filename_index_offset_bytes = -1;
+ hdr.zstd_dictionary_length_bytes = -1;
fwrite(&hdr, sizeof(hdr), 1, outfp);
- Corpus corpus(outfp, block_size);
+ // Train the dictionary by sampling real blocks.
+ // The documentation for ZDICT_trainFromBuffer() claims that a reasonable
+ // dictionary size is ~100 kB, but 1 kB seems to actually compress better for us,
+ // and decompress just as fast.
+ DictionaryBuilder builder(/*blocks_to_keep=*/1000, block_size);
+ read_mlocate(infile, &builder);
+ string dictionary = builder.train(1024);
+ ZSTD_CDict *cdict = ZSTD_createCDict(dictionary.data(), dictionary.size(), /*level=*/6);
+
+ hdr.zstd_dictionary_offset_bytes = ftell(outfp);
+ fwrite(dictionary.data(), dictionary.size(), 1, outfp);
+ hdr.zstd_dictionary_length_bytes = dictionary.size();
+ Corpus corpus(outfp, block_size, cdict);
read_mlocate(infile, &corpus);
if (false) { // To read a plain text file.
FILE *fp = fopen(infile, "r");
}
// Rewind, and write the updated header.
- hdr.version = 0;
+ hdr.version = 1;
fseek(outfp, 0, SEEK_SET);
fwrite(&hdr, sizeof(hdr), 1, outfp);
fclose(outfp);
size_t total_bytes __attribute__((unused)) = (bytes_for_hashtable + bytes_for_posting_lists + bytes_for_filename_index + bytes_for_filenames);
dprintf("Block size: %7d files\n", block_size);
+ dprintf("Dictionary: %'7.1f MB\n", dictionary.size() / 1048576.0);
dprintf("Hash table: %'7.1f MB\n", bytes_for_hashtable / 1048576.0);
dprintf("Posting lists: %'7.1f MB\n", bytes_for_posting_lists / 1048576.0);
dprintf("Filename index: %'7.1f MB\n", bytes_for_filename_index / 1048576.0);
projects / plocate / blobdiff