Function test_cache_erase

src/test/cuckoocache_tests.cpp:124–178

 * that the hit rate of "fresher" keys is reasonable*/
template <typename Cache>
static void test_cache_erase(size_t megabytes)
{
    double load = 1;
    SeedInsecureRand(SeedRand::ZEROS);
    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++) = InsecureRand32();
    }
    /** 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)
        BOOST_CHECK(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 as erased but 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)
{