[test] DisconnectedBlockTransactions::DynamicMemoryUsage

src/Makefile.test.include

@@ -92,6 +92,7 @@ BITCOIN_TESTS =\
   test/dbwrapper_tests.cpp \
   test/denialofservice_tests.cpp \
   test/descriptor_tests.cpp \
+  test/disconnected_transactions.cpp \
   test/flatfile_tests.cpp \
   test/fs_tests.cpp \
   test/getarg_tests.cpp \

src/test/disconnected_transactions.cpp

@@ -0,0 +1,95 @@
+// Copyright (c) 2023 The Bitcoin 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 <core_memusage.h>
+#include <kernel/disconnected_transactions.h>
+#include <test/util/setup_common.h>
+
+BOOST_FIXTURE_TEST_SUITE(disconnected_transactions, TestChain100Setup)
+
+//! Tests that DisconnectedBlockTransactions limits its own memory properly
+BOOST_AUTO_TEST_CASE(disconnectpool_memory_limits)
+{
+    // Use the coinbase transactions from TestChain100Setup. It doesn't matter whether these
+    // transactions would realistically be in a block together, they just need distinct txids and
+    // uniform size for this test to work.
+    std::vector<CTransactionRef> block_vtx(m_coinbase_txns);
+    BOOST_CHECK_EQUAL(block_vtx.size(), 100);
+
+    // Roughly estimate sizes to sanity check that DisconnectedBlockTransactions::DynamicMemoryUsage
+    // is within an expected range.
+
+    // Overhead for the hashmap depends on number of buckets
+    std::unordered_map<uint256, CTransaction*, SaltedTxidHasher> temp_map;
+    temp_map.reserve(1);
+    const size_t MAP_1{memusage::DynamicUsage(temp_map)};
+    temp_map.reserve(100);
+    const size_t MAP_100{memusage::DynamicUsage(temp_map)};
+
+    const size_t TX_USAGE{RecursiveDynamicUsage(block_vtx.front())};
+    for (const auto& tx : block_vtx)
+        BOOST_CHECK_EQUAL(RecursiveDynamicUsage(tx), TX_USAGE);
+
+    // Our overall formula is unordered map overhead + usage per entry.
+    // Implementations may vary, but we're trying to guess the usage of data structures.
+    const size_t ENTRY_USAGE_ESTIMATE{
+        TX_USAGE
+        // list entry: 2 pointers (next pointer and prev pointer) + element itself
+        + memusage::MallocUsage((2 * sizeof(void*)) + sizeof(decltype(block_vtx)::value_type))
+        // unordered map: 1 pointer for the hashtable + key and value
+        + memusage::MallocUsage(sizeof(void*) + sizeof(decltype(temp_map)::key_type)
+                                + sizeof(decltype(temp_map)::value_type))};
+
+    // DisconnectedBlockTransactions that's just big enough for 1 transaction.
+    {
+        DisconnectedBlockTransactions disconnectpool{MAP_1 + ENTRY_USAGE_ESTIMATE};
+        // Add just 2 (and not all 100) transactions to keep the unordered map's hashtable overhead
+        // to a minimum and avoid all (instead of all but 1) transactions getting evicted.
+        std::vector<CTransactionRef> two_txns({block_vtx.at(0), block_vtx.at(1)});
+        auto evicted_txns{disconnectpool.AddTransactionsFromBlock(two_txns)};
+        BOOST_CHECK(disconnectpool.DynamicMemoryUsage() <= MAP_1 + ENTRY_USAGE_ESTIMATE);
+
+        // Only 1 transaction can be kept
+        BOOST_CHECK_EQUAL(1, evicted_txns.size());
+        // Transactions are added from back to front and eviction is FIFO.
+        BOOST_CHECK_EQUAL(block_vtx.at(1), evicted_txns.front());
+
+        disconnectpool.clear();
+    }
+
+    // DisconnectedBlockTransactions with a comfortable maximum memory usage so that nothing is evicted.
+    // Record usage so we can check size limiting in the next test.
+    size_t usage_full{0};
+    {
+        const size_t USAGE_100_OVERESTIMATE{MAP_100 + ENTRY_USAGE_ESTIMATE * 100};
+        DisconnectedBlockTransactions disconnectpool{USAGE_100_OVERESTIMATE};
+        auto evicted_txns{disconnectpool.AddTransactionsFromBlock(block_vtx)};
+        BOOST_CHECK_EQUAL(evicted_txns.size(), 0);
+        BOOST_CHECK(disconnectpool.DynamicMemoryUsage() <= USAGE_100_OVERESTIMATE);
+
+        usage_full = disconnectpool.DynamicMemoryUsage();
+
+        disconnectpool.clear();
+    }
+
+    // DisconnectedBlockTransactions that's just a little too small for all of the transactions.
+    {
+        const size_t MAX_MEMUSAGE_99{usage_full - sizeof(void*)};
+        DisconnectedBlockTransactions disconnectpool{MAX_MEMUSAGE_99};
+        auto evicted_txns{disconnectpool.AddTransactionsFromBlock(block_vtx)};
+        BOOST_CHECK(disconnectpool.DynamicMemoryUsage() <= MAX_MEMUSAGE_99);
+
+        // Only 1 transaction needed to be evicted
+        BOOST_CHECK_EQUAL(1, evicted_txns.size());
+
+        // Transactions are added from back to front and eviction is FIFO.
+        // The last transaction of block_vtx should be the first to be evicted.
+        BOOST_CHECK_EQUAL(block_vtx.back(), evicted_txns.front());
+
+        disconnectpool.clear();
+    }
+}
+
+BOOST_AUTO_TEST_SUITE_END()