validation: add randomness to periodic write interval

Co-Authored-By: Pieter Wuille <[email protected]>
Co-Authored-By: l0rinc <[email protected]>

Author: 3 people

src/test/chainstate_write_tests.cpp

@@ -25,18 +25,18 @@ BOOST_FIXTURE_TEST_CASE(chainstate_write_interval, TestingSetup)
     auto& chainstate{Assert(m_node.chainman)->ActiveChainstate()};
     BlockValidationState state_dummy{};
 
-    // The first periodic flush sets m_last_write and does not flush
+    // The first periodic flush sets m_next_write and does not flush
     chainstate.FlushStateToDisk(state_dummy, FlushStateMode::PERIODIC);
     m_node.validation_signals->SyncWithValidationInterfaceQueue();
     BOOST_CHECK(!sub->m_did_flush);
 
-    // The periodic flush interval is 1 hour
-    SetMockTime(GetTime<std::chrono::minutes>() + 59min);
+    // The periodic flush interval is between 50 and 70 minutes (inclusive)
+    SetMockTime(GetTime<std::chrono::minutes>() + 49min);
     chainstate.FlushStateToDisk(state_dummy, FlushStateMode::PERIODIC);
     m_node.validation_signals->SyncWithValidationInterfaceQueue();
     BOOST_CHECK(!sub->m_did_flush);
 
-    SetMockTime(GetTime<std::chrono::minutes>() + 1h);
+    SetMockTime(GetTime<std::chrono::minutes>() + 70min);
     chainstate.FlushStateToDisk(state_dummy, FlushStateMode::PERIODIC);
     m_node.validation_signals->SyncWithValidationInterfaceQueue();
     BOOST_CHECK(sub->m_did_flush);

src/validation.cpp

@@ -90,8 +90,12 @@ using node::SnapshotMetadata;
 
 /** Size threshold for warning about slow UTXO set flush to disk. */
 static constexpr size_t WARN_FLUSH_COINS_SIZE = 1 << 30; // 1 GiB
-/** Time to wait between writing blocks/block index and chainstate to disk. */
-static constexpr std::chrono::hours DATABASE_WRITE_INTERVAL{1};
+/** Time window to wait between writing blocks/block index and chainstate to disk.
+ *  Randomize writing time inside the window to prevent a situation where the
+ *  network over time settles into a few cohorts of synchronized writers.
+*/
+static constexpr auto DATABASE_WRITE_INTERVAL_MIN{50min};
+static constexpr auto DATABASE_WRITE_INTERVAL_MAX{70min};
 /** Maximum age of our tip for us to be considered current for fee estimation */
 static constexpr std::chrono::hours MAX_FEE_ESTIMATION_TIP_AGE{3};
 const std::vector<std::string> CHECKLEVEL_DOC {
@@ -2945,7 +2949,8 @@ bool Chainstate::FlushStateToDisk(
         }
 
         if (should_write || m_next_write == NodeClock::time_point::max()) {
-            m_next_write = NodeClock::now() + DATABASE_WRITE_INTERVAL;
+            constexpr auto range{DATABASE_WRITE_INTERVAL_MAX - DATABASE_WRITE_INTERVAL_MIN};
+            m_next_write = FastRandomContext().rand_uniform_delay(NodeClock::now() + DATABASE_WRITE_INTERVAL_MIN, range);
         }
     }
     if (full_flush_completed && m_chainman.m_options.signals) {