fix(cluster_family): Cancel slot migration from incoming node on OOM

src/server/cluster/cluster_defs.h

@@ -172,12 +172,11 @@ class ClusterShardInfos {
 };
 
 // MigrationState constants are ordered in state changing order
-enum class MigrationState : uint8_t {
-  C_CONNECTING,
-  C_SYNC,
-  C_ERROR,
-  C_FINISHED,
-};
+enum class MigrationState : uint8_t { C_CONNECTING, C_SYNC, C_ERROR, C_FINISHED, C_FATAL };
+
+// Errors during slot migration
+static constexpr std::string_view kUnknownMigration = "UNKNOWN_MIGRATION";
+static constexpr std::string_view kIncomingMigrationOOM = "INCOMING_MIGRATION_OOM";
 
 // return error message if slot doesn't belong to this node
 facade::ErrorReply SlotOwnershipError(SlotId slot_id);

src/server/cluster/cluster_family.cc

@@ -726,6 +726,8 @@ static string_view StateToStr(MigrationState state) {
       return "ERROR"sv;
     case MigrationState::C_FINISHED:
       return "FINISHED"sv;
+    case MigrationState::C_FATAL:
+      return "FATAL"sv;
   }
   DCHECK(false) << "Unknown State value " << static_cast<underlying_type_t<MigrationState>>(state);
   return "UNDEFINED_STATE"sv;
@@ -765,7 +767,6 @@ void ClusterFamily::DflySlotMigrationStatus(CmdArgList args, SinkReplyBuilder* b
   };
 
   for (const auto& m : incoming_migrations_jobs_) {
-    // TODO add error status
     append_answer("in", m->GetSourceID(), node_id, m->GetState(), m->GetKeyCount(),
                   m->GetErrorStr());
   }
@@ -925,7 +926,7 @@ void ClusterFamily::InitMigration(CmdArgList args, SinkReplyBuilder* builder) {
 
   if (!migration) {
     VLOG(1) << "Unrecognized incoming migration from " << source_id;
-    return builder->SendSimpleString(OutgoingMigration::kUnknownMigration);
+    return builder->SendSimpleString(kUnknownMigration);
   }
 
   if (migration->GetState() != MigrationState::C_CONNECTING) {
@@ -936,6 +937,10 @@ void ClusterFamily::InitMigration(CmdArgList args, SinkReplyBuilder* builder) {
     DeleteSlots(slots);
   }
 
+  if (migration->GetState() == MigrationState::C_FATAL) {
+    return builder->SendError(absl::StrCat("-", kIncomingMigrationOOM));
+  }
+
   migration->Init(flows_num);
 
   return builder->SendOk();
@@ -955,6 +960,7 @@ void ClusterFamily::DflyMigrateFlow(CmdArgList args, SinkReplyBuilder* builder,
   cntx->conn()->SetName(absl::StrCat("migration_flow_", source_id));
 
   auto migration = GetIncomingMigration(source_id);
+
   if (!migration) {
     return builder->SendError(kIdNotFound);
   }
@@ -1033,15 +1039,19 @@ void ClusterFamily::DflyMigrateAck(CmdArgList args, SinkReplyBuilder* builder) {
                    [source_id = source_id](const auto& m) { return m.node_info.id == source_id; });
   if (m_it == in_migrations.end()) {
     LOG(WARNING) << "migration isn't in config";
-    return builder->SendError(OutgoingMigration::kUnknownMigration);
+    return builder->SendSimpleString(kUnknownMigration);
   }
 
   auto migration = GetIncomingMigration(source_id);
   if (!migration)
     return builder->SendError(kIdNotFound);
 
   if (!migration->Join(attempt)) {
-    return builder->SendError("Join timeout happened");
+    if (migration->GetState() == MigrationState::C_FATAL) {
+      return builder->SendError(absl::StrCat("-", kIncomingMigrationOOM));
+    } else {
+      return builder->SendError("Join timeout happened");
+    }
   }
 
   ApplyMigrationSlotRangeToConfig(migration->GetSourceID(), migration->GetSlots(), true);

src/server/cluster/incoming_slot_migration.cc

@@ -85,6 +85,11 @@ class ClusterShardMigration {
           VLOG(1) << "Finalized flow " << source_shard_id_;
           return;
         }
+        if (in_migration_->GetState() == MigrationState::C_FATAL) {
+          VLOG(1) << "Flow finalization " << source_shard_id_
+                  << " canceled due memory limit reached";
+          return;
+        }
         if (!tx_data->command.cmd_args.empty()) {
           VLOG(1) << "Flow finalization failed " << source_shard_id_ << " by "
                   << tx_data->command.cmd_args[0];
@@ -99,6 +104,12 @@ class ClusterShardMigration {
         // TODO check about ping logic
       } else {
         ExecuteTx(std::move(*tx_data), cntx);
+        // Break incoming slot migration if command reported OOM
+        if (executor_.connection_context()->IsOOM()) {
+          cntx->ReportError(std::string{kIncomingMigrationOOM});
+          in_migration_->ReportFatalError(std::string{kIncomingMigrationOOM});
+          break;
+        }
       }
     }
 
@@ -190,6 +201,11 @@ bool IncomingSlotMigration::Join(long attempt) {
       return false;
     }
 
+    // If any of migration shards reported ERROR (OOM) we can return error
+    if (GetState() == MigrationState::C_FATAL) {
+      return false;
+    }
+
     // if data was sent after LSN, WaitFor() always returns false so to reduce wait time
     // we check current state and if WaitFor false but GetLastAttempt() == attempt
     // the Join is failed and we can return false
@@ -227,6 +243,11 @@ void IncomingSlotMigration::Stop() {
     }
   }
 
+  // Don't wait if we reached FATAL state
+  if (state_ == MigrationState::C_FATAL) {
+    return;
+  }
+
   // we need to Join the migration process to prevent data corruption
   const absl::Time start = absl::Now();
   const absl::Duration timeout =
@@ -260,7 +281,12 @@ void IncomingSlotMigration::Init(uint32_t shards_num) {
 
 void IncomingSlotMigration::StartFlow(uint32_t shard, util::FiberSocketBase* source) {
   shard_flows_[shard]->Start(&cntx_, source);
-  VLOG(1) << "Incoming flow " << shard << " finished for " << source_id_;
+  VLOG(1) << "Incoming flow " << shard
+          << (GetState() == MigrationState::C_FINISHED ? " finished " : " cancelled ") << "for "
+          << source_id_;
+  if (GetState() == MigrationState::C_FATAL) {
+    Stop();
+  }
 }
 
 size_t IncomingSlotMigration::GetKeyCount() const {

src/server/cluster/incoming_slot_migration.h

@@ -50,10 +50,20 @@ class IncomingSlotMigration {
     return source_id_;
   }
 
+  // Switch to  FATAL state and store error message
+  void ReportFatalError(dfly::GenericError err) ABSL_LOCKS_EXCLUDED(state_mu_, error_mu_) {
+    errors_count_.fetch_add(1, std::memory_order_relaxed);
+    util::fb2::LockGuard lk_state(state_mu_);
+    util::fb2::LockGuard lk_error(error_mu_);
+    state_ = MigrationState::C_FATAL;
+    last_error_ = std::move(err);
+  }
+
   void ReportError(dfly::GenericError err) ABSL_LOCKS_EXCLUDED(error_mu_) {
     errors_count_.fetch_add(1, std::memory_order_relaxed);
     util::fb2::LockGuard lk(error_mu_);
-    last_error_ = std::move(err);
+    if (GetState() != MigrationState::C_FATAL)
+      last_error_ = std::move(err);
   }
 
   std::string GetErrorStr() const ABSL_LOCKS_EXCLUDED(error_mu_) {
@@ -75,6 +85,7 @@ class IncomingSlotMigration {
   std::vector<std::unique_ptr<ClusterShardMigration>> shard_flows_;
   SlotRanges slots_;
   ExecutionState cntx_;
+
   mutable util::fb2::Mutex error_mu_;
   dfly::GenericError last_error_ ABSL_GUARDED_BY(error_mu_);
   std::atomic<size_t> errors_count_ = 0;

src/server/cluster/outgoing_slot_migration.cc

@@ -145,7 +145,12 @@ void OutgoingMigration::OnAllShards(
 void OutgoingMigration::Finish(GenericError error) {
   auto next_state = MigrationState::C_FINISHED;
   if (error) {
-    next_state = MigrationState::C_ERROR;
+    // If OOM error move to FATAL, non-recoverable  state
+    if (error == errc::not_enough_memory) {
+      next_state = MigrationState::C_FATAL;
+    } else {
+      next_state = MigrationState::C_ERROR;
+    }
     LOG(WARNING) << "Finish outgoing migration for " << cf_->MyID() << ": "
                  << migration_info_.node_info.id << " with error: " << error.Format();
     exec_st_.ReportError(std::move(error));
@@ -168,6 +173,7 @@ void OutgoingMigration::Finish(GenericError error) {
 
       case MigrationState::C_SYNC:
       case MigrationState::C_ERROR:
+      case MigrationState::C_FATAL:
         should_cancel_flows = true;
         break;
     }
@@ -230,6 +236,13 @@ void OutgoingMigration::SyncFb() {
     }
 
     if (!CheckRespIsSimpleReply("OK")) {
+      // Break outgoing migration if INIT from incoming node responded with OOM. Usually this will
+      // happen on second iteration after first failed with OOM. Sending second INIT is required to
+      // cleanup slots on incoming slot migration node.
+      if (CheckRespSimpleError(kIncomingMigrationOOM)) {
+        ChangeState(MigrationState::C_FATAL);
+        break;
+      }
       if (CheckRespIsSimpleReply(kUnknownMigration)) {
         const absl::Duration passed = absl::Now() - start_time;
         // we provide 30 seconds to distribute the config to all nodes to avoid extra errors
@@ -280,7 +293,11 @@ void OutgoingMigration::SyncFb() {
 
     long attempt = 0;
     while (GetState() != MigrationState::C_FINISHED && !FinalizeMigration(++attempt)) {
-      // process commands that were on pause and try again
+      // Break loop and don't sleep in case of C_FATAL
+      if (GetState() == MigrationState::C_FATAL) {
+        break;
+      }
+      // Process commands that were on pause and try again
       VLOG(1) << "Waiting for migration to finalize...";
       ThisFiber::SleepFor(500ms);
     }
@@ -367,6 +384,13 @@ bool OutgoingMigration::FinalizeMigration(long attempt) {
       return false;
     }
 
+    // Check OOM from incoming slot migration on ACK request
+    if (CheckRespSimpleError(kIncomingMigrationOOM)) {
+      Finish(GenericError{std::make_error_code(errc::not_enough_memory),
+                          std::string(kIncomingMigrationOOM)});
+      return false;
+    }
+
     if (!CheckRespFirstTypes({RespExpr::INT64})) {
       LOG(WARNING) << "Incorrect response type for " << cf_->MyID() << " : "
                    << migration_info_.node_info.id << " attempt " << attempt

src/server/cluster/outgoing_slot_migration.h

@@ -76,8 +76,6 @@ class OutgoingMigration : private ProtocolClient {
 
   size_t GetKeyCount() const ABSL_LOCKS_EXCLUDED(state_mu_);
 
-  static constexpr std::string_view kUnknownMigration = "UNKNOWN_MIGRATION";
-
  private:
   // should be run for all shards
   void StartFlow(journal::Journal* journal, io::Sink* dest);

src/server/conn_context.h

@@ -295,6 +295,10 @@ class ConnectionContext : public facade::ConnectionContext {
     return conn_state.db_index;
   }
 
+  bool IsOOM() {
+    return std::exchange(is_oom_, false);
+  }
+
   void ChangeSubscription(bool to_add, bool to_reply, CmdArgList args,
                           facade::RedisReplyBuilder* rb);
 
@@ -323,6 +327,9 @@ class ConnectionContext : public facade::ConnectionContext {
   // The related connection is bound to main listener or serves the memcached protocol
   bool has_main_or_memcache_listener = false;
 
+  // OOM reported while executing
+  bool is_oom_ = false;
+
  private:
   void EnableMonitoring(bool enable) {
     subscriptions++;  // required to support the monitoring

src/server/journal/executor.cc

@@ -33,7 +33,7 @@ template <typename... Ts> journal::ParsedEntry::CmdData BuildFromParts(Ts... par
     start += part.size();
   }
 
-  return {std::move(buf), std::move(slice_parts)};
+  return {std::move(buf), std::move(slice_parts), cmd_str.size()};
 }
 }  // namespace
 

src/server/journal/serializer.cc

@@ -162,6 +162,7 @@ std::error_code JournalReader::ReadCommand(journal::ParsedEntry::CmdData* data)
 
   size_t cmd_size = 0;
   SET_OR_RETURN(ReadUInt<uint64_t>(), cmd_size);
+  data->cmd_len = cmd_size;
 
   // Read all strings consecutively.
   data->command_buf = make_unique<uint8_t[]>(cmd_size);
@@ -174,6 +175,9 @@ std::error_code JournalReader::ReadCommand(journal::ParsedEntry::CmdData* data)
     ptr += size;
     cmd_size -= size;
   }
+
+  data->cmd_len -= cmd_size;
+
   return {};
 }
 

src/server/journal/types.h

@@ -73,6 +73,7 @@ struct ParsedEntry : public EntryBase {
   struct CmdData {
     std::unique_ptr<uint8_t[]> command_buf;
     CmdArgVec cmd_args;  // represents the parsed command.
+    size_t cmd_len{0};
   };
   CmdData cmd;
 

src/server/main_service.cc

@@ -1405,6 +1405,10 @@ bool Service::InvokeCmd(const CommandId* cid, CmdArgList tail_args,
   }
 
   if (std::string reason = builder->ConsumeLastError(); !reason.empty()) {
+    // Set flag if OOM reported
+    if (reason == kOutOfMemory) {
+      cmd_cntx.conn_cntx->is_oom_ = true;
+    }
     VLOG(2) << FailedCommandToString(cid->name(), tail_args, reason);
     LOG_EVERY_T(WARNING, 1) << FailedCommandToString(cid->name(), tail_args, reason);
   }

src/server/protocol_client.cc

@@ -342,6 +342,11 @@ bool ProtocolClient::CheckRespIsSimpleReply(string_view reply) const {
          ToSV(resp_args_.front().GetBuf()) == reply;
 }
 
+bool ProtocolClient::CheckRespSimpleError(string_view error) const {
+  return resp_args_.size() == 1 && resp_args_.front().type == RespExpr::ERROR &&
+         ToSV(resp_args_.front().GetBuf()) == error;
+}
+
 bool ProtocolClient::CheckRespFirstTypes(initializer_list<RespExpr::Type> types) const {
   unsigned i = 0;
   for (RespExpr::Type type : types) {

src/server/protocol_client.h

@@ -85,6 +85,9 @@ class ProtocolClient {
   // Check if reps_args contains a simple reply.
   bool CheckRespIsSimpleReply(std::string_view reply) const;
 
+  // Check if resp_args contains a simple error
+  bool CheckRespSimpleError(std::string_view error) const;
+
   // Check resp_args contains the following types at front.
   bool CheckRespFirstTypes(std::initializer_list<facade::RespExpr::Type> types) const;
 

tests/dragonfly/cluster_test.py

@@ -3236,3 +3236,60 @@ async def test_cancel_blocking_cmd_during_mygration_finalization(df_factory: Dfl
     await push_config(json.dumps(generate_config(nodes)), [node.client for node in nodes])
 
     assert await c_nodes[1].type("list") == "none"
+
+
+@dfly_args({"cluster_mode": "yes"})
+async def test_slot_migration_oom(df_factory):
+    instances = [
+        df_factory.create(
+            port=next(next_port),
+            admin_port=next(next_port),
+            proactor_threads=4,
+            maxmemory="1024MB",
+        ),
+        df_factory.create(
+            port=next(next_port),
+            admin_port=next(next_port),
+            proactor_threads=2,
+            maxmemory="512MB",
+        ),
+    ]
+
+    df_factory.start_all(instances)
+
+    nodes = [(await create_node_info(instance)) for instance in instances]
+    nodes[0].slots = [(0, 16383)]
+    nodes[1].slots = []
+
+    await push_config(json.dumps(generate_config(nodes)), [node.admin_client for node in nodes])
+
+    await nodes[0].client.execute_command("DEBUG POPULATE 100 test 10000000")
+
+    nodes[0].migrations.append(
+        MigrationInfo("127.0.0.1", nodes[1].instance.admin_port, [(0, 16383)], nodes[1].id)
+    )
+
+    logging.info("Start migration")
+    await push_config(json.dumps(generate_config(nodes)), [node.admin_client for node in nodes])
+
+    # Wait for FATAL status
+    await wait_for_status(nodes[0].admin_client, nodes[1].id, "FATAL", 300)
+    await wait_for_status(nodes[1].admin_client, nodes[0].id, "FATAL")
+
+    # Node_0 slot-migration-status
+    status = await nodes[0].admin_client.execute_command(
+        "DFLYCLUSTER", "SLOT-MIGRATION-STATUS", nodes[1].id
+    )
+    # Direction
+    assert status[0][0] == "out"
+    # Error message
+    assert status[0][4] == "Cannot allocate memory: INCOMING_MIGRATION_OOM"
+
+    # Node_1 slot-migration-status
+    status = await nodes[1].admin_client.execute_command(
+        "DFLYCLUSTER", "SLOT-MIGRATION-STATUS", nodes[0].id
+    )
+    # Direction
+    assert status[0][0] == "in"
+    # Error message
+    assert status[0][4] == "INCOMING_MIGRATION_OOM"