Why queries are slow during load?

Users
4

btw, i have a lot of “old” transactions in logs. may be it’s the case:

2018/10/19 18:17:04 draft.go:769: Found 117 old transactions. Acting to abort them.
2018/10/19 18:17:04 draft.go:746: TryAbort 117 txns with start ts. Error: <nil>
2018/10/19 18:19:05 draft.go:772: abortOldTransactions for 117 txns. Error: <nil>
2018/10/19 18:20:08 draft.go:769: Found 192 old transactions. Acting to abort them.
2018/10/19 18:20:08 draft.go:746: TryAbort 192 txns with start ts. Error: <nil>
2018/10/19 18:23:48 draft.go:769: Found 64 old transactions. Acting to abort them.
2018/10/19 18:23:48 draft.go:746: TryAbort 64 txns with start ts. Error: <nil>
2018/10/19 18:24:02 draft.go:772: abortOldTransactions for 192 txns. Error: <nil>
2018/10/19 18:24:42 draft.go:772: abortOldTransactions for 64 txns. Error: <nil>
2018/10/19 18:26:03 draft.go:769: Found 84 old transactions. Acting to abort them.
2018/10/19 18:26:04 draft.go:746: TryAbort 84 txns with start ts. Error: <nil>
2018/10/19 18:27:17 draft.go:772: abortOldTransactions for 84 txns. Error: <nil>
2018/10/19 18:29:07 draft.go:769: Found 11 old transactions. Acting to abort them.
2018/10/19 18:29:07 draft.go:746: TryAbort 11 txns with start ts. Error: <nil>
2018/10/19 18:30:51 draft.go:772: abortOldTransactions for 11 txns. Error: <nil>
2018/10/19 18:32:44 draft.go:769: Found 227 old transactions. Acting to abort them.
2018/10/19 18:32:44 draft.go:746: TryAbort 227 txns with start ts. Error: <nil>

but in data load procedure i use autocommit, so have no idea how they appear:

  def runMutation(q: String): Unit = {
    val txn = dgraphClient.newTransaction
    try {
      val mu = Mutation.newBuilder()
        .setSetNquads(ByteString.copyFromUtf8(q))
        .setCommitNow(true)
        .setIgnoreIndexConflict(true)
        .build
      txn.mutate(mu)
    } catch {
      case e: Exception => {
        println(e.getMessage)
        //println(q)
      }
    } finally {
      txn.discard()
    }
  }