RAFT read bug

arangod/Agency/Agent.cpp

@@ -484,22 +484,22 @@ read_ret_t Agent::read(query_t const& query) {
   // Only leader else redirect
   if (!_constituent.leading()) {
     return read_ret_t(false, _constituent.leaderID());
-  }
-
-  // Still leading?
-  size_t good = 0; 
-  for (auto const& i : _lastAcked) {
-    std::chrono::duration<double> m =
-      std::chrono::system_clock::now() - i.second;
-    if(0.9*_config.minPing() > m.count()) {
-      ++good;
+  } else {
+    // Still leading?
+    size_t good = 0; 
+    for (auto const& i : _lastAcked) {
+      std::chrono::duration<double> m =
+        std::chrono::system_clock::now() - i.second;
+      if(0.9*_config.minPing() > m.count()) {
+        ++good;
+      }
+    }
+    if (good < size() / 2) {
+      _constituent.candidate();
+      return read_ret_t(false, NO_LEADER);
     }
   }
-  
-  if (good < size() / 2) {
-    _constituent.candidate();
-  }
-  
+
   // Retrieve data from readDB
   auto result = std::make_shared<arangodb::velocypack::Builder>();
   std::vector<bool> success = _readDB.read(query, result);

arangod/Agency/Constituent.cpp

@@ -214,6 +214,8 @@ void Constituent::lead(std::map<std::string, bool> const& votes) {
 void Constituent::candidate() {
   
   MUTEX_LOCKER(guard, _castLock);
+
+  _leaderID = NO_LEADER;
   
   if (_role != CANDIDATE)
     LOG_TOPIC(DEBUG, Logger::AGENCY)

arangod/Agency/RestAgencyHandler.cpp

@@ -140,9 +140,8 @@ RestHandler::status RestAgencyHandler::handleWrite() {
     }
 
     auto s = std::chrono::system_clock::now(); // Leadership established?
-    std::chrono::seconds timeout(1);
+    std::chrono::duration<double> timeout(_agent->config().minPing());
     while(_agent->size() > 1 && _agent->leaderID() == "") {
-      std::this_thread::sleep_for(duration_t(100));
       if ((std::chrono::system_clock::now()-s) > timeout) {
         Builder body;
         body.openObject();
@@ -153,12 +152,12 @@ RestHandler::status RestAgencyHandler::handleWrite() {
         LOG_TOPIC(ERR, Logger::AGENCY) << "We don't know who the leader is";
         return status::DONE;
       }
+      std::this_thread::sleep_for(duration_t(100));
     }
 
     write_ret_t ret = _agent->write(query);
 
     if (ret.accepted) {  // We're leading and handling the request
-
       bool found;
       std::string call_mode = _request->header("x-arangodb-agency-mode", found);
       if (!found) {
@@ -227,9 +226,8 @@ inline RestHandler::status RestAgencyHandler::handleRead() {
     }
 
     auto s = std::chrono::system_clock::now(); // Leadership established?
-    std::chrono::seconds timeout(1);
-    while(_agent->size() > 1 && _agent->leaderID() == "") {
-      std::this_thread::sleep_for(duration_t(100));
+    std::chrono::duration<double> timeout(_agent->config().minPing());
+    while(_agent->size() > 1 && _agent->leaderID() == NO_LEADER) {
       if ((std::chrono::system_clock::now()-s) > timeout) {
         Builder body;
         body.openObject();
@@ -240,6 +238,7 @@ inline RestHandler::status RestAgencyHandler::handleRead() {
         LOG_TOPIC(ERR, Logger::AGENCY) << "We don't know who the leader is";
         return status::DONE;
       }
+      std::this_thread::sleep_for(duration_t(100));
     }
 
     read_ret_t ret = _agent->read(query);
@@ -252,7 +251,20 @@ inline RestHandler::status RestAgencyHandler::handleRead() {
         generateResult(GeneralResponse::ResponseCode::OK, ret.result->slice());
       }
     } else {  // Redirect to leader
-      redirectRequest(ret.redirect);
+      if (_agent->leaderID() == NO_LEADER) {
+
+        Builder body;
+        body.openObject();
+        body.add("message", VPackValue("No leader"));
+        body.close();
+        generateResult(GeneralResponse::ResponseCode::SERVICE_UNAVAILABLE,
+                       body.slice());
+        LOG_TOPIC(ERR, Logger::AGENCY) << "We don't know who the leader is";
+        return status::DONE;
+        
+      } else {
+        redirectRequest(ret.redirect);
+      }
       return status::DONE;
     }
   } else {
@@ -263,6 +275,7 @@ inline RestHandler::status RestAgencyHandler::handleRead() {
 }
 
 RestHandler::status RestAgencyHandler::handleConfig() {
+  
   Builder body;
   body.add(VPackValue(VPackValueType::Object));
   body.add("term", Value(_agent->term()));