Refactor command request processing path to reduce BSON parsing passes

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      There are several calls to BSONObj::getField that are made by functions called by ExecCommandDatabase::_initiateCommand and ExecCommandDatabase::run.

      They come from the following places:

      • Multiple calls to OpMsgRequest::getDbName
      • _extractReadConcern
      • commandSpecifiesWriteConcern
      • searches for "shardVersion" and "databaseVersion"
      • ReadPreferenceSetting::fromInnerBSON
      • VectorClock::PlainComponentFormat::in and VectorClock::SignedComponentFormat::in

      Additionally, there are two manual loops over BSONOjb fields:

      • readRequestMetadata
      • ExecCommandDatabase::_initiateCommand

      Finally, we invoke 2 IDL parser in addition to the one for the command

      • APIParametersFromClient
      • OperationSessionInfoFromClient

      Example of the request fields that can be consolidated in an IDL definition:

      structs:
  CommonRequestArgs:
    description: TODO
    strict: false
    unsafe_dangerous_disable_extra_field_duplicate_checks: true
    chained_structs:
      APIParametersFromClient: APIParametersFromClient
      OperationSessionInfoFromClientBase: OperationSessionInfoFromClientBase
      ClusterTimesCommon: ClusterTimesCommon
    fields:
      readConcern:
        type: object
        optional: true
      databaseVersion:
          type: database_version
          optional: true
      shardVersion:
          type: shard_version
          optional: true
      writeConcern:
        type: IDLAnyType
        optional: true
      $readPreference:
        type: IDLAnyType
        cpp_name: readPreference
        optional: true
      $client:
        type: IDLAnyType
        cpp_name: clientMetadata
        optional: true
      tracking_info:
        type: IDLAnyType
        optional: true
      $audit:
        cpp_name: impersonation
        type: IDLAnyType
        optional: true
      clientOperationKey:
        type: uuid
        optional: true
      mayBypassWriteBlocking:
        type: IDLAnyType
        optional: true
      maxTimeMS:
        type: maxTimeMS
        optional: true
        validator: { gte: 0 }
      maxTimeMSOpOnly:
        type: maxTimeMS
        optional: true
        validator: { gte: 0 }
      help:
        type: safeBool
        optional: true
      comment:
        type: IDLAnyType
        optional: true
      $maxTimeMS:
        type: IDLAnyType
        cpp_name: queryOptionMaxTimeMS
        optional: true

      Note: There may be opportunity to align with the request fields defined in src/mongo/idl/generic_argument.idl. On the other hand, a more narrow parser for this error handling will be better then a wider parser handling all generic request fields.

      POC: https://github.com/markbenvenuto/mongo/tree/tiger_perf_bson

            Assignee:
            Alex Li
            Reporter:
            Mark Benvenuto
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              Created:
              Updated:
              Resolved: