Periodically refresh read transaction inside hinted scheduler (#4325)

nano/node/scheduler/hinted.cpp

@@ -59,13 +59,15 @@ bool nano::scheduler::hinted::predicate () const
 	return active.vacancy (nano::election_behavior::hinted) > 0;
 }
 
-void nano::scheduler::hinted::activate (const nano::store::transaction & transaction, const nano::block_hash & hash, bool check_dependents)
+void nano::scheduler::hinted::activate (const nano::store::read_transaction & transaction, const nano::block_hash & hash, bool check_dependents)
 {
 	std::stack<nano::block_hash> stack;
 	stack.push (hash);
 
 	while (!stack.empty ())
 	{
+		transaction.refresh_if_needed ();
+
 		const nano::block_hash current_hash = stack.top ();
 		stack.pop ();
 
@@ -115,9 +117,12 @@ void nano::scheduler::hinted::run_iterative ()
 	const auto minimum_tally = tally_threshold ();
 	const auto minimum_final_tally = final_tally_threshold ();
 
+	// Get the list before db transaction starts to avoid unnecessary slowdowns
+	auto tops = vote_cache.top (minimum_tally);
+
 	auto transaction = node.store.tx_begin_read ();
 
-	for (auto const & entry : vote_cache.top (minimum_tally))
+	for (auto const & entry : tops)
 	{
 		if (!predicate ())
 		{

nano/node/scheduler/hinted.hpp

@@ -3,6 +3,7 @@
 #include <nano/lib/locks.hpp>
 #include <nano/lib/numbers.hpp>
 #include <nano/secure/common.hpp>
+#include <nano/store/transaction.hpp>
 
 #include <boost/multi_index/hashed_index.hpp>
 #include <boost/multi_index/ordered_index.hpp>
@@ -61,7 +62,7 @@ class hinted final
 	bool predicate () const;
 	void run ();
 	void run_iterative ();
-	void activate (nano::store::transaction const &, nano::block_hash const & hash, bool check_dependents);
+	void activate (nano::store::read_transaction const &, nano::block_hash const & hash, bool check_dependents);
 
 	nano::uint128_t tally_threshold () const;
 	nano::uint128_t final_tally_threshold () const;

nano/store/transaction.cpp

@@ -36,6 +36,7 @@ nano::store::write_transaction_impl::write_transaction_impl (nano::id_dispenser:
 nano::store::read_transaction::read_transaction (std::unique_ptr<store::read_transaction_impl> read_transaction_impl) :
 	impl (std::move (read_transaction_impl))
 {
+	start = std::chrono::steady_clock::now ();
 }
 
 void * nano::store::read_transaction::get_handle () const
@@ -56,6 +57,7 @@ void nano::store::read_transaction::reset () const
 void nano::store::read_transaction::renew () const
 {
 	impl->renew ();
+	start = std::chrono::steady_clock::now ();
 }
 
 void nano::store::read_transaction::refresh () const
@@ -64,6 +66,15 @@ void nano::store::read_transaction::refresh () const
 	renew ();
 }
 
+void nano::store::read_transaction::refresh_if_needed (std::chrono::milliseconds max_age) const
+{
+	auto now = std::chrono::steady_clock::now ();
+	if (now - start > max_age)
+	{
+		refresh ();
+	}
+}
+
 /*
  * write_transaction
  */
@@ -75,6 +86,8 @@ nano::store::write_transaction::write_transaction (std::unique_ptr<store::write_
 	 * For IO threads, we do not want them to block on creating write transactions.
 	 */
 	debug_assert (nano::thread_role::get () != nano::thread_role::name::io);
+
+	start = std::chrono::steady_clock::now ();
 }
 
 void * nano::store::write_transaction::get_handle () const
@@ -95,12 +108,22 @@ void nano::store::write_transaction::commit ()
 void nano::store::write_transaction::renew ()
 {
 	impl->renew ();
+	start = std::chrono::steady_clock::now ();
 }
 
 void nano::store::write_transaction::refresh ()
 {
-	impl->commit ();
-	impl->renew ();
+	commit ();
+	renew ();
+}
+
+void nano::store::write_transaction::refresh_if_needed (std::chrono::milliseconds max_age)
+{
+	auto now = std::chrono::steady_clock::now ();
+	if (now - start > max_age)
+	{
+		refresh ();
+	}
 }
 
 bool nano::store::write_transaction::contains (nano::tables table_a) const

nano/store/transaction.hpp

@@ -56,9 +56,11 @@ class read_transaction final : public transaction
 	void reset () const;
 	void renew () const;
 	void refresh () const;
+	void refresh_if_needed (std::chrono::milliseconds max_age = std::chrono::milliseconds{ 500 }) const;
 
 private:
 	std::unique_ptr<read_transaction_impl> impl;
+	mutable std::chrono::steady_clock::time_point start;
 };
 
 /**
@@ -75,9 +77,11 @@ class write_transaction final : public transaction
 	void commit ();
 	void renew ();
 	void refresh ();
+	void refresh_if_needed (std::chrono::milliseconds max_age = std::chrono::milliseconds{ 500 });
 	bool contains (nano::tables table_a) const;
 
 private:
 	std::unique_ptr<write_transaction_impl> impl;
+	std::chrono::steady_clock::time_point start;
 };
 } // namespace nano::store