Add some benchmark calculations to bench.cpp.

diff --git a/bench.cpp b/bench.cpp
index 03b3967ac4ab4eddb8752e5028795ebc4f93191b..6ab0494dcacd2159b08c0c16936fc0874272378a 100644 (file)
--- a/bench.cpp
+++ b/bench.cpp
@@ -29,6 +29,7 @@ int main(void)
        unique_ptr<Trigram[]> ht(new Trigram[hdr.hashtable_size + hdr.extra_ht_slots + 1]);
        complete_pread(fd, ht.get(), (hdr.hashtable_size + hdr.extra_ht_slots + 1) * sizeof(Trigram), hdr.hash_table_offset_bytes);
 
+       size_t posting_list_bytes = 0, total_elements = 0;
        uint32_t longest_pl = 0;
        vector<pair<string, unsigned>> posting_lists;
        for (unsigned i = 0; i < hdr.hashtable_size + hdr.extra_ht_slots; ++i) {
@@ -41,6 +42,8 @@ int main(void)
                complete_pread(fd, &str[0], len, ht[i].offset);
                posting_lists.emplace_back(move(str), ht[i].num_docids);
                longest_pl = std::max(ht[i].num_docids, longest_pl);
+               posting_list_bytes += len;
+               total_elements += ht[i].num_docids;
        }
        ht.reset();
        fprintf(stderr, "Read %zu posting lists.\n", posting_lists.size());
@@ -86,4 +89,15 @@ int main(void)
        end = steady_clock::now();
        double own_sec = duration<double>(end - start).count();
        fprintf(stderr, "Decoding with own implementation: %.3f ms (%.2f%% speed)\n", 1e3 * own_sec, 100.0 * reference_sec / own_sec);
+
+       // Three numbers giving rules of thumb for judging our own implementation:
+       //
+       // - Compressed speed is easy to compare to disk I/O, to see the relative importance
+       // - Uncompressed speed is easy to compare to intersection speeds and memory bandwidth
+       //   (also very roughly comparable to the benchmark numbers in the TurboPFor README)
+       // - ns/element gives an absolute measure for plocate (e.g. if we can decompress at
+       //   1 ns/element, a 10k-element posting list goes by in 0.01 ms, which is way beyond
+       //   instantaneous in practice).
+       fprintf(stderr, "%.1f MB/sec (compressed), %.1f MB/sec (uncompressed), %.1f ns/element\n", posting_list_bytes / own_sec / 1048576.0,
+               (total_elements * sizeof(uint32_t)) / own_sec / 1048576.0, 1e9 * own_sec / total_elements);
 }