最近，当我用spark和hbase测试集群时。我使用newapihadooprdd从hbase表读取记录。我发现newapihadooprdd太慢了，而且时间与区域服务器的数量成正比。
下面的spark debug（opened for test）日志显示了该过程：

17/03/02 22:00:30 DEBUG AbstractRpcClient: Use SIMPLE authentication for service ClientService, sasl=false
17/03/02 22:00:30 DEBUG AbstractRpcClient: Connecting to slave111/192.168.10.111:16020
17/03/02 22:00:30 DEBUG ClientCnxn: Reading reply sessionid:0x15a8de8a86f0444, packet:: clientPath:null serverPath:null finished:false header:: 5,3  replyHeader:: 5,116079898,0  request:: '/hbase,F  response:: s{116070329,116070329,1488462020202,1488462020202,0,16,0,0,0,16,116070652} 
17/03/02 22:00:30 DEBUG ClientCnxn: Reading reply sessionid:0x15a8de8a86f0444, packet:: clientPath:null serverPath:null finished:false header:: 6,4  replyHeader:: 6,116079898,0  request:: '/hbase/master,F  response:: #ffffffff000146d61737465723a3136303030fffffff4ffffffa23affffffc8ffffffb6ffffffb1ffffffc21a50425546a12a66d617374657210ffffff807d18ffffffcffffffff4fffffffffffffff9ffffffa82b10018ffffff8a7d,s{116070348,116070348,1488462021202,1488462021202,0,0,0,97546372339663909,54,0,116070348} 
17/03/02 22:00:30 DEBUG AbstractRpcClient: Use SIMPLE authentication for service MasterService, sasl=false
17/03/02 22:00:30 DEBUG AbstractRpcClient: Connecting to master/192.168.10.100:16000
17/03/02 22:00:30 DEBUG RegionSizeCalculator: Region tt,3,1488442069431.21d34666d310df3f180b2dba093d910d. has size 0
17/03/02 22:00:30 DEBUG RegionSizeCalculator: Region tt,,1488442069431.cb8696957957f824f1a16210768bf197. has size 0
17/03/02 22:00:30 DEBUG RegionSizeCalculator: Region tt,1,1488442069431.274ddaa4abb34f0408cac0f33107529c. has size 0
17/03/02 22:00:30 DEBUG RegionSizeCalculator: Region tt,2,1488442069431.05dd84aacb7f2587e325c8baf4c27613. has size 0
17/03/02 22:00:30 DEBUG RegionSizeCalculator: Region sizes calculated
17/03/02 22:00:38 DEBUG Client: IPC Client (480943798) connection to master/192.168.10.100:9000 from hadoop: closed
17/03/02 22:00:38 DEBUG Client: IPC Client (480943798) connection to master/192.168.10.100:9000 from hadoop: stopped, remaining connections 0
17/03/02 22:00:43 DEBUG ClientCnxn: Got ping response for sessionid: 0x15a8de8a86f0444 after 0ms
17/03/02 22:00:56 DEBUG ClientCnxn: Got ping response for sessionid: 0x15a8de8a86f0444 after 0ms
17/03/02 22:01:00 DEBUG TableInputFormatBase: getSplits: split -> 0 -> HBase table split(table name: tt, scan: , start row: , end row: 1, region location: slave104)
17/03/02 22:01:10 DEBUG ClientCnxn: Got ping response for sessionid: 0x15a8de8a86f0444 after 0ms
17/03/02 22:01:23 DEBUG ClientCnxn: Got ping response for sessionid: 0x15a8de8a86f0444 after 0ms
17/03/02 22:01:30 DEBUG TableInputFormatBase: getSplits: split -> 1 -> HBase table split(table name: tt, scan: , start row: 1, end row: 2, region location: slave102)
17/03/02 22:01:37 DEBUG ClientCnxn: Got ping response for sessionid: 0x15a8de8a86f0444 after 0ms
17/03/02 22:01:50 DEBUG ClientCnxn: Got ping response for sessionid: 0x15a8de8a86f0444 after 0ms
17/03/02 22:02:00 DEBUG TableInputFormatBase: getSplits: split -> 2 -> HBase table split(table name: tt, scan: , start row: 2, end row: 3, region location: slave112)
17/03/02 22:02:03 DEBUG ClientCnxn: Got ping response for sessionid: 0x15a8de8a86f0444 after 0ms
17/03/02 22:02:17 DEBUG ClientCnxn: Got ping response for sessionid: 0x15a8de8a86f0444 after 0ms
17/03/02 22:02:30 DEBUG ClientCnxn: Got ping response for sessionid: 0x15a8de8a86f0444 after 0ms
17/03/02 22:02:30 DEBUG TableInputFormatBase: getSplits: split -> 3 -> HBase table split(table name: tt, scan: , start row: 3, end row: , region location: slave108)
17/03/02 22:02:30 INFO ConnectionManager$HConnectionImplementation: Closing master protocol: MasterService
17/03/02 22:02:30 INFO ConnectionManager$HConnectionImplementation: Closing zookeeper sessionid=0x15a8de8a86f0444
17/03/02 22:02:30 DEBUG ZooKeeper: Closing session: 0x15a8de8a86f0444
17/03/02 22:02:30 DEBUG ClientCnxn: Closing client for session: 0x15a8de8a86f0444
17/03/02 22:02:30 DEBUG ClientCnxn: Reading reply sessionid:0x15a8de8a86f0444, packet:: clientPath:null serverPath:null finished:false header:: 7,-11  replyHeader:: 7,116080795,0  request:: null response:: null
17/03/02 22:02:30 DEBUG ClientCnxn: Disconnecting client for session: 0x15a8de8a86f0444
17/03/02 22:02:30 INFO ZooKeeper: Session: 0x15a8de8a86f0444 closed
17/03/02 22:02:30 INFO ClientCnxn: EventThread shut down
17/03/02 22:02:30 DEBUG AbstractRpcClient: Stopping rpc client
17/03/02 22:02:30 DEBUG ClientCnxn: An exception was thrown while closing send thread for session 0x15a8de8a86f0444 : Unable to read additional data from server sessionid 0x15a8de8a86f0444, likely server has closed socket
17/03/02 22:02:30 DEBUG ClosureCleaner: +++ Cleaning closure <function1> (org.apache.spark.rdd.RDD$$anonfun$count$1) +++

我使用的是spark 2.1.0和hbase 1.1.2。getsplits操作花费了太多时间。区域服务器号从1到4进行测试，每个区域服务器需要30秒。hbase表不包含任何记录（仅用于测试）。
这正常吗？有人和我有同样的问题吗？
测试代码如下：

Configuration hconf = HBaseConfiguration.create();
hconf.set(TableInputFormat.INPUT_TABLE, GLOBAL.TABLE_NAME);
hconf.set("hbase.zookeeper.quorum", "192.168.10.100");
hconf.set("hbase.zookeeper.property.clientPort", "2181");
Scan scan = new Scan();

JavaPairRDD<ImmutableBytesWritable, Result> results
        = sc.newAPIHadoopRDD(hconf, TableInputFormat.class, ImmutableBytesWritable.class, Result.class);

long cnt = results.count();
System.out.println(cnt);

编辑
用hbase源代码调试后，我发现了速度慢的原因。罪魁祸首是tableinputformatbase.java中的反向dns操作。

ipAddressString = DNS.reverseDns(ipAddress, null);

现在如何解决这个问题？我可以在hbase配置中添加一些dns ip对吗？