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Date: Wed, 12 Oct 2016 11:28:20 +0000 (UTC)
From: "Lars George (JIRA)" <jira@apache.org>
To: dev@hbase.apache.org
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Subject: [jira] [Created] (HBASE-16815) Low scan ratio in RPC queue tuning
 triggers divide by zero exception
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archived-at: Wed, 12 Oct 2016 11:28:23 -0000

Lars George created HBASE-16815:
-----------------------------------

             Summary: Low scan ratio in RPC queue tuning triggers divide by zero exception
                 Key: HBASE-16815
                 URL: https://issues.apache.org/jira/browse/HBASE-16815
             Project: HBase
          Issue Type: Bug
          Components: regionserver, rpc
    Affects Versions: 2.0.0, 1.3.0
            Reporter: Lars George


Trying the following settings:

{noformat}
<property>
  <name>hbase.ipc.server.callqueue.handler.factor</name>
  <value>0.5</value>
</property>
<property>
  <name>hbase.ipc.server.callqueue.read.ratio</name>
  <value>0.5</value>
</property>
<property>
  <name>hbase.ipc.server.callqueue.scan.ratio</name>
  <value>0.1</value>
</property>
{noformat}

With 30 default handlers, this means 15 queues. Further, it means 8 write queues and 7 read queues. 10% of that is {{0.7}} which is then floor'ed to {{0}}. The debug log confirms it, as the tertiary check omits the scan details when they are zero:

{noformat}
2016-10-12 12:50:27,305 INFO  [main] ipc.SimpleRpcScheduler: Using fifo as user call queue, count=15
2016-10-12 12:50:27,311 DEBUG [main] ipc.RWQueueRpcExecutor: FifoRWQ.default writeQueues=7 writeHandlers=15 readQueues=8 readHandlers=14
{noformat}

But the code in {{RWQueueRpcExecutor}} calls {{RpcExecutor.startHandler()}} nevertheless and that does this:

{code}
    for (int i = 0; i < numHandlers; i++) {
      final int index = qindex + (i % qsize);
      String name = "RpcServer." + threadPrefix + ".handler=" + handlers.size() + ",queue=" +
          index + ",port=" + port;
{code}

The modulo triggers then 

{noformat}
2016-10-12 11:41:22,810 ERROR [main] master.HMasterCommandLine: Master exiting
java.lang.RuntimeException: Failed construction of Master: class org.apache.hadoop.hbase.master.HMasterCommandLine$LocalHMaster
        at org.apache.hadoop.hbase.util.JVMClusterUtil.createMasterThread(JVMClusterUtil.java:145)
        at org.apache.hadoop.hbase.LocalHBaseCluster.addMaster(LocalHBaseCluster.java:220)
        at org.apache.hadoop.hbase.LocalHBaseCluster.(LocalHBaseCluster.java:155)
        at org.apache.hadoop.hbase.master.HMasterCommandLine.startMaster(HMasterCommandLine.java:222)
        at org.apache.hadoop.hbase.master.HMasterCommandLine.run(HMasterCommandLine.java:137)
        at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:70)
        at org.apache.hadoop.hbase.util.ServerCommandLine.doMain(ServerCommandLine.java:126)
        at org.apache.hadoop.hbase.master.HMaster.main(HMaster.java:2524)
Caused by: java.lang.ArithmeticException: / by zero
        at org.apache.hadoop.hbase.ipc.RpcExecutor.startHandlers(RpcExecutor.java:125)
        at org.apache.hadoop.hbase.ipc.RWQueueRpcExecutor.startHandlers(RWQueueRpcExecutor.java:178)
        at org.apache.hadoop.hbase.ipc.RpcExecutor.start(RpcExecutor.java:78)
        at org.apache.hadoop.hbase.ipc.SimpleRpcScheduler.start(SimpleRpcScheduler.java:272)
        at org.apache.hadoop.hbase.ipc.RpcServer.start(RpcServer.java:2212)
        at org.apache.hadoop.hbase.regionserver.RSRpcServices.start(RSRpcServices.java:1143)
        at org.apache.hadoop.hbase.regionserver.HRegionServer.(HRegionServer.java:615)
        at org.apache.hadoop.hbase.master.HMaster.(HMaster.java:396)
        at org.apache.hadoop.hbase.master.HMasterCommandLine$LocalHMaster.(HMasterCommandLine.java:312)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:422)
        at org.apache.hadoop.hbase.util.JVMClusterUtil.createMasterThread(JVMClusterUtil.java:140)
        ... 7 more
{noformat}

That causes the server to not even start. I would suggest we either skip the {{startHandler()}} call altogether, or make it zero aware.

Another possible option is to reserve at least _one_ scan handler/queue when the scan ratio is greater than zero, but only of there is more than one read handler/queue to begin with. Otherwise the scan handler/queue should be zero and share the one read handler/queue.

Makes sense?



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