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  1. Core Server
  2. SERVER-16102

Contention on mutex protecting canAcceptWritesForDatabase access with WT

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    • Operating System:
      ALL

      Description

      Running sysbench and profiling with VTune, the lock protecting canAccpetWritesForDatabase resulted very contented, even if mongod is
      run as standalone.

          bool ReplicationCoordinatorImpl::canAcceptWritesForDatabase(const StringData& dbName) {
              // we must check _settings since getReplicationMode() isn't aware of modeReplSet
              // until a valid replica set config has been loaded
              boost::lock_guard<boost::mutex> lk(_mutex);
              if (_settings.usingReplSets()) {
                  if (_getReplicationMode_inlock() == modeReplSet &&
                          _getCurrentMemberState_inlock().primary() &&
                          !_isWaitingForDrainToComplete) {
                      return true;
                  }
                  return dbName == "local";
              }

      Code inspection shows up that, some functions, e.g. newRunQuery() call replication code unconditionally, i.e.

              // uassert if we are not on a primary, and not a secondary with SlaveOk query parameter set.
              bool slaveOK = pq.getOptions().slaveOk || pq.hasReadPref();
              status = repl::getGlobalReplicationCoordinator()->checkCanServeReadsFor(
                      txn,
                      NamespaceString(cq->ns()),
                      slaveOK);
              uassertStatusOK(status);

      Hence, during high load that mutex might become a bottleneck.
      Vtune stacktraces, together with lock percentages:

      Waiting Call Stack
      1 of 7: 43.4% (493.236s of 1135.355s)
       
      mongod!boost::mutex::lock+0x17 - mutex.hpp:59
      mongod!lock_guard+0xb - locks.hpp:257
      mongod!mongo::repl::ReplicationCoordinatorImpl::canAcceptWritesForDatabase+0xe - repl_coordinator_impl.cpp:1195
      mongod!mongo::repl::ReplicationCoordinatorImpl::checkCanServeReadsFor+0x4a - repl_coordinator_impl.cpp:1227
      mongod!mongo::newRunQuery+0x74d - new_find.cpp:672
      mongod!receivedQuery+0x1f2 - instance.cpp:220
      mongod!mongo::assembleResponse+0x9d0 - instance.cpp:393
      mongod!mongo::MyMessageHandler::process+0xdf - db.cpp:185
      mongod!mongo::PortMessageServer::handleIncomingMsg+0x420 - message_server_port.cpp:234
      libpthread-2.18.so!start_thread+0xc2 - [Unknown]:[Unknown]
      libc-2.18.so!__clone+0x6c - [Unknown]:[Unknown]

      Waiting Call Stack
      2 of 7: 23.0% (261.345s of 1135.355s)
       
      mongod!boost::mutex::lock+0x17 - mutex.hpp:59
      mongod!lock_guard+0xb - locks.hpp:257
      mongod!mongo::repl::ReplicationCoordinatorImpl::canAcceptWritesForDatabase+0xe - repl_coordinator_impl.cpp:1195
      mongod!mongo::Command::execCommand+0x5da - dbcommands.cpp:1319
      mongod!mongo::_runCommands+0x221 - dbcommands.cpp:1464
      mongod!runCommands+0x23 - new_find.cpp:131
      mongod!mongo::newRunQuery+0xff9 - new_find.cpp:551
      mongod!receivedQuery+0x1f2 - instance.cpp:220
      mongod!mongo::assembleResponse+0x9d0 - instance.cpp:393
      mongod!mongo::MyMessageHandler::process+0xdf - db.cpp:185
      mongod!mongo::PortMessageServer::handleIncomingMsg+0x420 - message_server_port.cpp:234
      libpthread-2.18.so!start_thread+0xc2 - [Unknown]:[Unknown]
      libc-2.18.so!__clone+0x6c - [Unknown]:[Unknown]

      Waiting Call Stack
      3 of 7: 12.4% (140.897s of 1135.355s)
       
      mongod!boost::mutex::lock+0x17 - mutex.hpp:59
      mongod!lock_guard+0xb - locks.hpp:257
      mongod!mongo::repl::ReplicationCoordinatorImpl::canAcceptWritesForDatabase+0xe - repl_coordinator_impl.cpp:1195
      mongod!mongo::UpdateStage::restoreUpdateState+0xb4 - update.cpp:831
      mongod!mongo::UpdateStage::restoreState+0x2f - update.cpp:858
      mongod!mongo::UpdateStage::work+0x2b9 - update.cpp:786
      mongod!mongo::PlanExecutor::getNext+0x99 - plan_executor.cpp:288
      mongod!mongo::PlanExecutor::executePlan+0x3c - plan_executor.cpp:400
      mongod!mongo::UpdateExecutor::execute+0x130 - update_executor.cpp:214
      mongod!multiUpdate+0x498 - batch_executor.cpp:1273
      mongod!mongo::WriteBatchExecutor::execUpdate+0x79 - batch_executor.cpp:880
      mongod!mongo::WriteBatchExecutor::bulkExecute+0x1f1 - batch_executor.cpp:761
      mongod!mongo::WriteBatchExecutor::executeBatch+0x3a4 - batch_executor.cpp:263
      mongod!mongo::WriteCmd::run+0x168 - write_commands.cpp:143
      mongod!mongo::_execCommand+0x33 - dbcommands.cpp:1174
      mongod!mongo::Command::execCommand+0xca0 - dbcommands.cpp:1388
      mongod!mongo::_runCommands+0x221 - dbcommands.cpp:1464
      mongod!runCommands+0x23 - new_find.cpp:131
      mongod!mongo::newRunQuery+0xff9 - new_find.cpp:551
      mongod!receivedQuery+0x1f2 - instance.cpp:220
      mongod!mongo::assembleResponse+0x9d0 - instance.cpp:393
      mongod!mongo::MyMessageHandler::process+0xdf - db.cpp:185
      mongod!mongo::PortMessageServer::handleIncomingMsg+0x420 - message_server_port.cpp:234
      libpthread-2.18.so!start_thread+0xc2 - [Unknown]:[Unknown]
      libc-2.18.so!__clone+0x6c - [Unknown]:[Unknown]

      Waiting Call Stack
      4 of 7: 7.5% (85.389s of 1135.355s)
       
      mongod!boost::mutex::lock+0x17 - mutex.hpp:59
      mongod!lock_guard+0xb - locks.hpp:257
      mongod!mongo::repl::ReplicationCoordinatorImpl::canAcceptWritesForDatabase+0xe - repl_coordinator_impl.cpp:1195
      mongod!mongo::UpdateExecutor::prepareInLock+0x2df - update_executor.cpp:154
      mongod!mongo::UpdateExecutor::execute+0xfe - update_executor.cpp:206
      mongod!multiUpdate+0x498 - batch_executor.cpp:1273
      mongod!mongo::WriteBatchExecutor::execUpdate+0x79 - batch_executor.cpp:880
      mongod!mongo::WriteBatchExecutor::bulkExecute+0x1f1 - batch_executor.cpp:761
      mongod!mongo::WriteBatchExecutor::executeBatch+0x3a4 - batch_executor.cpp:263
      mongod!mongo::WriteCmd::run+0x168 - write_commands.cpp:143
      mongod!mongo::_execCommand+0x33 - dbcommands.cpp:1174
      mongod!mongo::Command::execCommand+0xca0 - dbcommands.cpp:1388
      mongod!mongo::_runCommands+0x221 - dbcommands.cpp:1464
      mongod!runCommands+0x23 - new_find.cpp:131
      mongod!mongo::newRunQuery+0xff9 - new_find.cpp:551
      mongod!receivedQuery+0x1f2 - instance.cpp:220
      mongod!mongo::assembleResponse+0x9d0 - instance.cpp:393
      mongod!mongo::MyMessageHandler::process+0xdf - db.cpp:185
      mongod!mongo::PortMessageServer::handleIncomingMsg+0x420 - message_server_port.cpp:234
      libpthread-2.18.so!start_thread+0xc2 - [Unknown]:[Unknown]
      libc-2.18.so!__clone+0x6c - [Unknown]:[Unknown]

      Waiting Call Stack
      5 of 7: 5.8% (66.230s of 1135.355s)
       
      mongod!boost::mutex::lock+0x17 - mutex.hpp:59
      mongod!lock_guard+0xb - locks.hpp:257
      mongod!mongo::repl::ReplicationCoordinatorImpl::canAcceptWritesForDatabase+0xe - repl_coordinator_impl.cpp:1195
      mongod!mongo::DeleteStage::restoreState+0x7c - delete.cpp:172
      mongod!mongo::DeleteStage::work+0x28e - delete.cpp:131
      mongod!mongo::PlanExecutor::getNext+0x99 - plan_executor.cpp:288
      mongod!mongo::PlanExecutor::executePlan+0x3c - plan_executor.cpp:400
      mongod!mongo::DeleteExecutor::execute+0x59 - delete_executor.cpp:185
      mongod!multiRemove+0x267 - batch_executor.cpp:1358
      mongod!mongo::WriteBatchExecutor::execRemove+0x74 - batch_executor.cpp:909
      mongod!mongo::WriteBatchExecutor::bulkExecute+0xf4 - batch_executor.cpp:782
      mongod!mongo::WriteBatchExecutor::executeBatch+0x3a4 - batch_executor.cpp:263
      mongod!mongo::WriteCmd::run+0x168 - write_commands.cpp:143
      mongod!mongo::_execCommand+0x33 - dbcommands.cpp:1174
      mongod!mongo::Command::execCommand+0xca0 - dbcommands.cpp:1388
      mongod!mongo::_runCommands+0x221 - dbcommands.cpp:1464
      mongod!runCommands+0x23 - new_find.cpp:131
      mongod!mongo::newRunQuery+0xff9 - new_find.cpp:551
      mongod!receivedQuery+0x1f2 - instance.cpp:220
      mongod!mongo::assembleResponse+0x9d0 - instance.cpp:393
      mongod!mongo::MyMessageHandler::process+0xdf - db.cpp:185
      mongod!mongo::PortMessageServer::handleIncomingMsg+0x420 - message_server_port.cpp:234
      libpthread-2.18.so!start_thread+0xc2 - [Unknown]:[Unknown]
      libc-2.18.so!__clone+0x6c - [Unknown]:[Unknown]

      Waiting Call Stack
      6 of 7: 3.9% (44.155s of 1135.355s)
       
      mongod!boost::mutex::lock+0x17 - mutex.hpp:59
      mongod!lock_guard+0xb - locks.hpp:257
      mongod!mongo::repl::ReplicationCoordinatorImpl::canAcceptWritesForDatabase+0xe - repl_coordinator_impl.cpp:1195
      mongod!checkIsMasterForDatabase+0x7e - batch_executor.cpp:461
      mongod!mongo::WriteBatchExecutor::ExecInsertsState::_lockAndCheckImpl+0x2f4 - batch_executor.cpp:966
      mongod!lockAndCheck+0x119 - batch_executor.cpp:1009
      mongod!insertOne+0x8f - batch_executor.cpp:1037
      mongod!mongo::WriteBatchExecutor::execOneInsert+0x5f - batch_executor.cpp:1065
      mongod!mongo::WriteBatchExecutor::execInserts+0x22c - batch_executor.cpp:860
      mongod!mongo::WriteBatchExecutor::bulkExecute+0x33 - batch_executor.cpp:754
      mongod!mongo::WriteBatchExecutor::executeBatch+0x3a4 - batch_executor.cpp:263
      mongod!mongo::WriteCmd::run+0x168 - write_commands.cpp:143
      mongod!mongo::_execCommand+0x33 - dbcommands.cpp:1174
      mongod!mongo::Command::execCommand+0xca0 - dbcommands.cpp:1388
      mongod!mongo::_runCommands+0x221 - dbcommands.cpp:1464
      mongod!runCommands+0x23 - new_find.cpp:131
      mongod!mongo::newRunQuery+0xff9 - new_find.cpp:551
      mongod!receivedQuery+0x1f2 - instance.cpp:220
      mongod!mongo::assembleResponse+0x9d0 - instance.cpp:393
      mongod!mongo::MyMessageHandler::process+0xdf - db.cpp:185
      mongod!mongo::PortMessageServer::handleIncomingMsg+0x420 - message_server_port.cpp:234
      libpthread-2.18.so!start_thread+0xc2 - [Unknown]:[Unknown]
      libc-2.18.so!__clone+0x6c - [Unknown]:[Unknown]

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            Assignee:
            schwerin Andy Schwerin
            Reporter:
            davide.italiano Davide Italiano
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              Updated:
              Resolved: