cuckoocache_tests.cpp

// Copyright (c) 2016-2018 The Bitcoin Core developers
// Copyright (c) 2017 The Raven Core developers
// Copyright (c) 2018 The Rito Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#include <boost/test/unit_test.hpp>
#include "cuckoocache.h"
#include "script/sigcache.h"
#include "test/test_rito.h"
#include "random.h"
#include <thread>

/** Test Suite for CuckooCache
 *
 *  1) All tests should have a deterministic result (using insecure rand
 *  with deterministic seeds)
 *  2) Some test methods are templated to allow for easier testing
 *  against new versions / comparing
 *  3) Results should be treated as a regression test, i.e., did the behavior
 *  change significantly from what was expected. This can be OK, depending on
 *  the nature of the change, but requires updating the tests to reflect the new
 *  expected behavior. For example improving the hit rate may cause some tests
 *  using BOOST_CHECK_CLOSE to fail.
 *
 */
FastRandomContext local_rand_ctx(true);

BOOST_AUTO_TEST_SUITE(cuckoocache_tests);


/** insecure_GetRandHash fills in a uint256 from local_rand_ctx
 */
    void insecure_GetRandHash(uint256 &t)
    {
        uint32_t *ptr = (uint32_t *) t.begin();
        for (uint8_t j = 0; j < 8; ++j)
            *(ptr++) = local_rand_ctx.rand32();
    }



/* Test that no values not inserted into the cache are read out of it.
 *
 * There are no repeats in the first 200000 insecure_GetRandHash calls
 */
    BOOST_AUTO_TEST_CASE(test_cuckoocache_no_fakes_test)
    {
        BOOST_TEST_MESSAGE("Running CuckooCache No Fakes Test");

        local_rand_ctx = FastRandomContext(true);
        CuckooCache::cache<uint256, SignatureCacheHasher> cc{};
        size_t megabytes = 4;
        cc.setup_bytes(megabytes << 20);
        uint256 v;
        for (int x = 0; x < 100000; ++x)
        {
            insecure_GetRandHash(v);
            cc.insert(v);
        }
        for (int x = 0; x < 100000; ++x)
        {
            insecure_GetRandHash(v);
            BOOST_CHECK(!cc.contains(v, false));
        }
    };

/** This helper returns the hit rate when megabytes*load worth of entries are
 * inserted into a megabytes sized cache
 */
    template<typename Cache>
    double test_cache(size_t megabytes, double load)
    {
        local_rand_ctx = FastRandomContext(true);
        std::vector<uint256> hashes;
        Cache set{};
        size_t bytes = megabytes * (1 << 20);
        set.setup_bytes(bytes);
        uint32_t n_insert = static_cast<uint32_t>(load * (bytes / sizeof(uint256)));
        hashes.resize(n_insert);
        for (uint32_t i = 0; i < n_insert; ++i)
        {
            uint32_t *ptr = (uint32_t *) hashes[i].begin();
            for (uint8_t j = 0; j < 8; ++j)
                *(ptr++) = local_rand_ctx.rand32();
        }
        /** We make a copy of the hashes because future optimizations of the
         * cuckoocache may overwrite the inserted element, so the test is
         * "future proofed".
         */
        std::vector<uint256> hashes_insert_copy = hashes;
        /** Do the insert */
        for (uint256 &h : hashes_insert_copy)
            set.insert(h);
        /** Count the hits */
        uint32_t count = 0;
        for (uint256 &h : hashes)
            count += set.contains(h, false);
        double hit_rate = ((double) count) / ((double) n_insert);
        return hit_rate;
    }

/** The normalized hit rate for a given load.
 *
 * The semantics are a little confusing, so please see the below
 * explanation.
 *
 * Examples:
 *
 * 1) at load 0.5, we expect a perfect hit rate, so we multiply by
 * 1.0
 * 2) at load 2.0, we expect to see half the entries, so a perfect hit rate
 * would be 0.5. Therefore, if we see a hit rate of 0.4, 0.4*2.0 = 0.8 is the
 * normalized hit rate.
 *
 * This is basically the right semantics, but has a bit of a glitch depending on
 * how you measure around load 1.0 as after load 1.0 your normalized hit rate
 * becomes effectively perfect, ignoring freshness.
 */
    double normalize_hit_rate(double hits, double load)
    {
        return hits * std::max(load, 1.0);
    }

/** Check the hit rate on loads ranging from 0.1 to 2.0 */
    BOOST_AUTO_TEST_CASE(cuckoocache_hit_rate_ok_test)
    {
        BOOST_TEST_MESSAGE("Running CuckooCache Hit Rate OK Test");

        /** Arbitrarily selected Hit Rate threshold that happens to work for this test
         * as a lower bound on performance.
         */
        double HitRateThresh = 0.98;
        size_t megabytes = 4;
        for (double load = 0.1; load < 2; load *= 2)
        {
            double hits = test_cache<CuckooCache::cache<uint256, SignatureCacheHasher>>(megabytes, load);
            BOOST_CHECK(normalize_hit_rate(hits, load) > HitRateThresh);
        }
    }


/** This helper checks that erased elements are preferentially inserted onto and
 * that the hit rate of "fresher" keys is reasonable*/
    template<typename Cache>
    void test_cache_erase(size_t megabytes)
    {
        double load = 1;
        local_rand_ctx = FastRandomContext(true);
        std::vector<uint256> hashes;
        Cache set{};
        size_t bytes = megabytes * (1 << 20);
        set.setup_bytes(bytes);
        uint32_t n_insert = static_cast<uint32_t>(load * (bytes / sizeof(uint256)));
        hashes.resize(n_insert);
        for (uint32_t i = 0; i < n_insert; ++i)
        {
            uint32_t *ptr = (uint32_t *) hashes[i].begin();
            for (uint8_t j = 0; j < 8; ++j)
                *(ptr++) = local_rand_ctx.rand32();
        }
        /** We make a copy of the hashes because future optimizations of the
         * cuckoocache may overwrite the inserted element, so the test is
         * "future proofed".
         */
        std::vector<uint256> hashes_insert_copy = hashes;

        /** Insert the first half */
        for (uint32_t i = 0; i < (n_insert / 2); ++i)
            set.insert(hashes_insert_copy[i]);
        /** Erase the first quarter */
        for (uint32_t i = 0; i < (n_insert / 4); ++i)
            set.contains(hashes[i], true);
        /** Insert the second half */
        for (uint32_t i = (n_insert / 2); i < n_insert; ++i)
            set.insert(hashes_insert_copy[i]);

        /** elements that we marked erased but that are still there */
        size_t count_erased_but_contained = 0;
        /** elements that we did not erase but are older */
        size_t count_stale = 0;
        /** elements that were most recently inserted */
        size_t count_fresh = 0;

        for (uint32_t i = 0; i < (n_insert / 4); ++i)
            count_erased_but_contained += set.contains(hashes[i], false);
        for (uint32_t i = (n_insert / 4); i < (n_insert / 2); ++i)
            count_stale += set.contains(hashes[i], false);
        for (uint32_t i = (n_insert / 2); i < n_insert; ++i)
            count_fresh += set.contains(hashes[i], false);

        double hit_rate_erased_but_contained = double(count_erased_but_contained) / (double(n_insert) / 4.0);
        double hit_rate_stale = double(count_stale) / (double(n_insert) / 4.0);
        double hit_rate_fresh = double(count_fresh) / (double(n_insert) / 2.0);

        // Check that our hit_rate_fresh is perfect
        BOOST_CHECK_EQUAL(hit_rate_fresh, 1.0);
        // Check that we have a more than 2x better hit rate on stale elements than
        // erased elements.
        BOOST_CHECK(hit_rate_stale > 2 * hit_rate_erased_but_contained);
    }

    BOOST_AUTO_TEST_CASE(cuckoocache_erase_ok_test)
    {
        BOOST_TEST_MESSAGE("Running CuckooCache Erase OK Test");

        size_t megabytes = 4;
        test_cache_erase<CuckooCache::cache<uint256, SignatureCacheHasher>>(megabytes);
    }

    template<typename Cache>
    void test_cache_erase_parallel(size_t megabytes)
    {
        double load = 1;
        local_rand_ctx = FastRandomContext(true);
        std::vector<uint256> hashes;
        Cache set{};
        size_t bytes = megabytes * (1 << 20);
        set.setup_bytes(bytes);
        uint32_t n_insert = static_cast<uint32_t>(load * (bytes / sizeof(uint256)));
        hashes.resize(n_insert);
        for (uint32_t i = 0; i < n_insert; ++i)
        {
            uint32_t *ptr = (uint32_t *) hashes[i].begin();
            for (uint8_t j = 0; j < 8; ++j)
                *(ptr++) = local_rand_ctx.rand32();
        }
        /** We make a copy of the hashes because future optimizations of the
         * cuckoocache may overwrite the inserted element, so the test is
         * "future proofed".
         */
        std::vector<uint256> hashes_insert_copy = hashes;
        boost::shared_mutex mtx;

        {
            /** Grab lock to make sure we release inserts */
            boost::unique_lock<boost::shared_mutex> l(mtx);
            /** Insert the first half */
            for (uint32_t i = 0; i < (n_insert / 2); ++i)
                set.insert(hashes_insert_copy[i]);
        }

        /** Spin up 3 threads to run contains with erase.
         */
        std::vector<std::thread> threads;
        /** Erase the first quarter */
        for (uint32_t x = 0; x < 3; ++x)
            /** Each thread is emplaced with x copy-by-value
            */
            threads.emplace_back([&, x]
                                 {
                                     boost::shared_lock<boost::shared_mutex> l(mtx);
                                     size_t ntodo = (n_insert / 4) / 3;
                                     size_t start = ntodo * x;
                                     size_t end = ntodo * (x + 1);
                                     for (uint32_t i = start; i < end; ++i)
                                         set.contains(hashes[i], true);
                                 });

        /** Wait for all threads to finish
         */
        for (std::thread &t : threads)
            t.join();
        /** Grab lock to make sure we observe erases */
        boost::unique_lock<boost::shared_mutex> l(mtx);
        /** Insert the second half */
        for (uint32_t i = (n_insert / 2); i < n_insert; ++i)
            set.insert(hashes_insert_copy[i]);

        /** elements that we marked erased but that are still there */
        size_t count_erased_but_contained = 0;
        /** elements that we did not erase but are older */
        size_t count_stale = 0;
        /** elements that were most recently inserted */
        size_t count_fresh = 0;

        for (uint32_t i = 0; i < (n_insert / 4); ++i)
            count_erased_but_contained += set.contains(hashes[i], false);
        for (uint32_t i = (n_insert / 4); i < (n_insert / 2); ++i)
            count_stale += set.contains(hashes[i], false);
        for (uint32_t i = (n_insert / 2); i < n_insert; ++i)
            count_fresh += set.contains(hashes[i], false);

        double hit_rate_erased_but_contained = double(count_erased_but_contained) / (double(n_insert) / 4.0);
        double hit_rate_stale = double(count_stale) / (double(n_insert) / 4.0);
        double hit_rate_fresh = double(count_fresh) / (double(n_insert) / 2.0);

        // Check that our hit_rate_fresh is perfect
        BOOST_CHECK_EQUAL(hit_rate_fresh, 1.0);
        // Check that we have a more than 2x better hit rate on stale elements than
        // erased elements.
        BOOST_CHECK(hit_rate_stale > 2 * hit_rate_erased_but_contained);
    }

    BOOST_AUTO_TEST_CASE(cuckoocache_erase_parallel_ok_test)
    {
        BOOST_TEST_MESSAGE("Running CuckooCache Erase Parallel OK Test");

        size_t megabytes = 4;
        test_cache_erase_parallel<CuckooCache::cache<uint256, SignatureCacheHasher>>(megabytes);
    }


    template<typename Cache>
    void test_cache_generations()
    {
        // This test checks that for a simulation of network activity, the fresh hit
        // rate is never below 99%, and the number of times that it is worse than
        // 99.9% are less than 1% of the time.
        double min_hit_rate = 0.99;
        double tight_hit_rate = 0.999;
        double max_rate_less_than_tight_hit_rate = 0.01;
        // A cache that meets this specification is therefore shown to have a hit
        // rate of at least tight_hit_rate * (1 - max_rate_less_than_tight_hit_rate) +
        // min_hit_rate*max_rate_less_than_tight_hit_rate = 0.999*99%+0.99*1% == 99.89%
        // hit rate with low variance.

        // We use deterministic values, but this test has also passed on many
        // iterations with non-deterministic values, so it isn't "overfit" to the
        // specific entropy in FastRandomContext(true) and implementation of the
        // cache.
        local_rand_ctx = FastRandomContext(true);

        // block_activity models a chunk of network activity. n_insert elements are
        // adde to the cache. The first and last n/4 are stored for removal later
        // and the middle n/2 are not stored. This models a network which uses half
        // the signatures of recently (since the last block) added transactions
        // immediately and never uses the other half.
        struct block_activity
        {
            std::vector<uint256> reads;

            block_activity(uint32_t n_insert, Cache &c) : reads()
            {
                std::vector<uint256> inserts;
                inserts.resize(n_insert);
                reads.reserve(n_insert / 2);
                for (uint32_t i = 0; i < n_insert; ++i)
                {
                    uint32_t *ptr = (uint32_t *) inserts[i].begin();
                    for (uint8_t j = 0; j < 8; ++j)
                        *(ptr++) = local_rand_ctx.rand32();
                }
                for (uint32_t i = 0; i < n_insert / 4; ++i)
                    reads.push_back(inserts[i]);
                for (uint32_t i = n_insert - (n_insert / 4); i < n_insert; ++i)
                    reads.push_back(inserts[i]);
                for (auto h : inserts)
                    c.insert(h);
            }
        };

        const uint32_t BLOCK_SIZE = 1000;
        // We expect window size 60 to perform reasonably given that each epoch
        // stores 45% of the cache size (~472k).
        const uint32_t WINDOW_SIZE = 60;
        const uint32_t POP_AMOUNT = (BLOCK_SIZE / WINDOW_SIZE) / 2;
        const double load = 10;
        const size_t megabytes = 4;
        const size_t bytes = megabytes * (1 << 20);
        const uint32_t n_insert = static_cast<uint32_t>(load * (bytes / sizeof(uint256)));

        std::vector<block_activity> hashes;
        Cache set{};
        set.setup_bytes(bytes);
        hashes.reserve(n_insert / BLOCK_SIZE);
        std::deque<block_activity> last_few;
        uint32_t out_of_tight_tolerance = 0;
        uint32_t total = n_insert / BLOCK_SIZE;
        // we use the deque last_few to model a sliding window of blocks. at each
        // step, each of the last WINDOW_SIZE block_activities checks the cache for
        // POP_AMOUNT of the hashes that they inserted, and marks these erased.
        for (uint32_t i = 0; i < total; ++i)
        {
            if (last_few.size() == WINDOW_SIZE)
                last_few.pop_front();
            last_few.emplace_back(BLOCK_SIZE, set);
            uint32_t count = 0;
            for (auto &act : last_few)
                for (uint32_t k = 0; k < POP_AMOUNT; ++k)
                {
                    count += set.contains(act.reads.back(), true);
                    act.reads.pop_back();
                }
            // We use last_few.size() rather than WINDOW_SIZE for the correct
            // behavior on the first WINDOW_SIZE iterations where the deque is not
            // full yet.
            double hit = (double(count)) / (last_few.size() * POP_AMOUNT);
            // Loose Check that hit rate is above min_hit_rate
            BOOST_CHECK(hit > min_hit_rate);
            // Tighter check, count number of times we are less than tight_hit_rate
            // (and implicitly, greater than min_hit_rate)
            out_of_tight_tolerance += hit < tight_hit_rate;
        }
        // Check that being out of tolerance happens less than
        // max_rate_less_than_tight_hit_rate of the time
        BOOST_CHECK(double(out_of_tight_tolerance) / double(total) < max_rate_less_than_tight_hit_rate);
    }

    BOOST_AUTO_TEST_CASE(cuckoocache_generations_test)
    {
        BOOST_TEST_MESSAGE("Running CuckooCache Generations Test");

        test_cache_generations<CuckooCache::cache<uint256, SignatureCacheHasher>>();
    }

BOOST_AUTO_TEST_SUITE_END();