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  1. Core Server
  2. SERVER-18242

mongos lock contention in mongo::Shard::findIfExists

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    Details

    • Type: Bug
    • Status: Closed
    • Priority: Critical - P2
    • Resolution: Fixed
    • Affects Version/s: 3.1.1, 3.1.2
    • Fix Version/s: 3.1.3
    • Component/s: Sharding
    • Labels:

      Description

      during test scalability of mongos/shard, found performance regression of mongos due to lock sleep

      the traffic is YCSB

      • single doc insert
      • shard with {_id: hashed}
      • total 7 shards, each is 3 member replica set
      • writer with 64 threads
      • only change mongos binary, 3.1.1/3.1.2 show lower throughput.
          3.0.2 3.1.2
        throughput 43451 7065

      from off-cpu perf analysis

      ## with master 3.1.2 (c8e2c0546b30621f78cd436d96714cc064bbb8a7)
       
      -36.26%-- futex_wait_queue_me
          futex_wait
          do_futex
          sys_futex
          system_call_fastpath
          |
          |--100.00%-- __lll_lock_wait
          |     |
          |     |--85.34%-- mongo::StaticShardInfo::reload()
          |     |    |
          |     |    |--100.00%-- mongo::Shard::findIfExists(std::string const&)
          |     |    |     mongo::DBClientShardResolver::chooseWriteHost(std::string const&, mongo::ConnectionString*) const
          |     |    |     mongo::BatchWriteExec::executeBatch(mongo::BatchedCommandRequest const&, mongo::BatchedCommandResponse*
          |     |    |     mongo::ClusterWriter::write(mongo::BatchedCommandRequest const&, mongo::BatchedCommandResponse*)
          |     |    |     |
          |     |    |      --100.00%-- mongo::(anonymous namespace)::ClusterWriteCmd::run(mongo::OperationContext*, std::string c
          |     |    |           mongo::Command::execCommandClientBasic(mongo::OperationContext*, mongo::Command*, mongo::Cli
          |     |    |           mongo::Command::runAgainstRegistered(char const*, mongo::BSONObj&, mongo::BSONObjBuilder&, i
          |     |    |           mongo::Strategy::clientCommandOp(mongo::Request&)
          |     |    |           mongo::Request::process(int)
          |     |    |           mongo::ShardedMessageHandler::process(mongo::Message&, mongo::AbstractMessagingPort*, mongo:
          |     |    |           mongo::PortMessageServer::handleIncomingMsg(void*)
          |     |    |           start_thread
          |     |     --0.00%-- [...]
          |     |
          |     |--14.42%-- mongo::Shard::findIfExists(std::string const&)
          |     |    mongo::DBClientShardResolver::chooseWriteHost(std::string const&, mongo::ConnectionString*) const
          |     |    mongo::BatchWriteExec::executeBatch(mongo::BatchedCommandRequest const&, mongo::BatchedCommandResponse*)
          |     |    mongo::ClusterWriter::write(mongo::BatchedCommandRequest const&, mongo::BatchedCommandResponse*)
          |     |    |
          |     |     --100.00%-- mongo::(anonymous namespace)::ClusterWriteCmd::run(mongo::OperationContext*, std::string const&, mong
          |     |          mongo::Command::execCommandClientBasic(mongo::OperationContext*, mongo::Command*, mongo::ClientBasic&,
          |     |          mongo::Command::runAgainstRegistered(char const*, mongo::BSONObj&, mongo::BSONObjBuilder&, int)
          |     |          mongo::Strategy::clientCommandOp(mongo::Request&)
          |     |          mongo::Request::process(int)
          |     |          mongo::ShardedMessageHandler::process(mongo::Message&, mongo::AbstractMessagingPort*, mongo::LastError*
          |     |          mongo::PortMessageServer::handleIncomingMsg(void*)
          |     |          start_thread
          |      --0.24%-- [...]
           --0.00%-- [...]
      

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