+#include <assert.h>
#include <stdio.h>
#include <string.h>
#include <algorithm>
#include <sys/stat.h>
#include <zstd.h>
+#define VINT_IN
+#include "vint.h"
#include "vp4.h"
#define P4NENC_BOUND(n) ((n+127)/128+(n+32)*sizeof(uint32_t))
uint8_t pad[4];
};
+class PostingListBuilder {
+public:
+ void add_docid(uint32_t docid);
+ void finish();
+
+ string encoded;
+ size_t num_docids = 0;
+
+private:
+ void write_header(uint32_t docid);
+ void append_block();
+
+ uint32_t pending_docids[128];
+ unsigned num_pending_docids = 0;
+
+ uint32_t last_block_end;
+};
+
+void PostingListBuilder::add_docid(uint32_t docid)
+{
+ // Deduplicate against the last inserted value, if any.
+ if (num_pending_docids == 0) {
+ if (encoded.empty()) {
+ // Very first docid.
+ write_header(docid);
+ ++num_docids;
+ last_block_end = docid;
+ return;
+ } else if (docid == last_block_end) {
+ return;
+ }
+ } else {
+ if (docid == pending_docids[num_pending_docids - 1]) {
+ return;
+ }
+ }
+
+ pending_docids[num_pending_docids++] = docid;
+ if (num_pending_docids == 128) {
+ append_block();
+ num_pending_docids = 0;
+ last_block_end = docid;
+ }
+ ++num_docids;
+}
+
+void PostingListBuilder::finish()
+{
+ if (num_pending_docids == 0) {
+ return;
+ }
+
+ assert(!encoded.empty()); // write_header() should already have run.
+
+ // No interleaving for partial blocks.
+ unsigned char buf[P4NENC_BOUND(128)];
+ unsigned char *end = p4d1enc32(pending_docids, num_pending_docids, buf, last_block_end);
+ encoded.append(reinterpret_cast<char *>(buf), reinterpret_cast<char *>(end));
+}
+
+void PostingListBuilder::append_block()
+{
+ unsigned char buf[P4NENC_BOUND(128)];
+ assert(num_pending_docids == 128);
+ unsigned char *end = p4d1enc128v32(pending_docids, 128, buf, last_block_end);
+ encoded.append(reinterpret_cast<char *>(buf), reinterpret_cast<char *>(end));
+}
+
+void PostingListBuilder::write_header(uint32_t docid)
+{
+ unsigned char buf[P4NENC_BOUND(1)];
+ size_t bytes = p4nd1enc128v32(&docid, 1, buf);
+ encoded.append(reinterpret_cast<char *>(buf), bytes);
+}
+
class Corpus {
public:
Corpus(size_t block_size) : block_size(block_size) {}
void flush_block();
vector<string> filename_blocks;
- unordered_map<uint32_t, vector<uint32_t>> invindex;
+ unordered_map<uint32_t, PostingListBuilder> invindex;
size_t num_files = 0, num_files_in_block = 0, num_blocks = 0;
private:
if (s.size() >= 3) {
for (size_t j = 0; j < s.size() - 2; ++j) {
uint32_t trgm = read_trigram(s, j);
- vector<uint32_t> &docids = invindex[trgm];
- if (docids.empty() || docids.back() != docid) {
- docids.push_back(docid);
- }
+ invindex[trgm].add_docid(docid);
}
}
ptr += s.size() + 1;
corpus.flush_block();
dprintf("Read %zu files from %s\n", corpus.num_files, infile);
- // Compress posting lists.
- string buf;
size_t trigrams = 0, longest_posting_list = 0;
size_t bytes_used = 0;
- unordered_map<uint32_t, string> pl;
- for (auto &[trigram, docids] : corpus.invindex) {
- longest_posting_list = max(longest_posting_list, docids.size());
- trigrams += docids.size();
-
- size_t bytes_needed = P4NENC_BOUND(docids.size());
- if (buf.size() < bytes_needed) buf.resize(bytes_needed);
- size_t bytes = p4nd1enc128v32(&docids[0], docids.size(), reinterpret_cast<unsigned char *>(&buf[0]));
- pl[trigram] = string(buf.data(), bytes);
- bytes_used += bytes;
+ for (auto &[trigram, pl_builder] : corpus.invindex) {
+ pl_builder.finish();
+ longest_posting_list = max(longest_posting_list, pl_builder.num_docids);
+ trigrams += pl_builder.num_docids;
+ bytes_used += pl_builder.encoded.size();
}
dprintf("%zu files, %zu different trigrams, %zu entries, avg len %.2f, longest %zu\n",
corpus.num_files, corpus.invindex.size(), trigrams, double(trigrams) / corpus.invindex.size(), longest_posting_list);
-
dprintf("%zu bytes used for posting lists (%.2f bits/entry)\n", bytes_used, 8 * bytes_used / double(trigrams));
+
//steady_clock::time_point end = steady_clock::now();
dprintf("Building posting lists took %.1f ms.\n\n", 1e3 * duration<float>(end - start).count());
vector<uint32_t> all_trigrams;
- for (auto &[trigram, docids] : corpus.invindex) {
+ for (auto &[trigram, pl_builder] : corpus.invindex) {
all_trigrams.push_back(trigram);
}
sort(all_trigrams.begin(), all_trigrams.end());
// Find out where the posting lists will end.
uint64_t offset = sizeof(uint64_t) * 2 + 16 * all_trigrams.size();
uint64_t filename_index_offset = offset;
- for (uint32_t trgm : all_trigrams) {
- filename_index_offset += pl[trgm].size();
+ for (auto &[trigram, pl_builder] : corpus.invindex) {
+ filename_index_offset += pl_builder.encoded.size();
}
fwrite(&filename_index_offset, sizeof(filename_index_offset), 1, outfp);
size_t bytes_for_trigrams = 0, bytes_for_posting_lists = 0, bytes_for_filename_index = 0, bytes_for_filenames = 0;
-
for (uint32_t trgm : all_trigrams) {
// 16 bytes: trgm (4), number of docids (4), byte offset (8)
fwrite(&trgm, sizeof(trgm), 1, outfp); // One byte wasted, but OK.
- uint32_t num_docids = corpus.invindex[trgm].size();
+ const PostingListBuilder &pl_builder = corpus.invindex[trgm];
+ uint32_t num_docids = pl_builder.num_docids;
fwrite(&num_docids, sizeof(num_docids), 1, outfp);
fwrite(&offset, sizeof(offset), 1, outfp);
- offset += pl[trgm].size();
+ offset += pl_builder.encoded.size();
bytes_for_trigrams += 16;
}
// Write the actual posting lists.
for (uint32_t trgm : all_trigrams) {
- fwrite(pl[trgm].data(), pl[trgm].size(), 1, outfp);
- bytes_for_posting_lists += pl[trgm].size();
+ const string &encoded = corpus.invindex[trgm].encoded;
+ fwrite(encoded.data(), encoded.size(), 1, outfp);
+ bytes_for_posting_lists += encoded.size();
}
// Stick an empty block at the end as sentinel.