毕设开发日志2017-12-01-Scan超时

【前言】

　　本篇博客主要描述一下在开发过程中遇到的scan的超时问题。

【问题描述】

　　刚刚完成了对索引表的定义和建议，并且在单元测试中对该表进行插入和扫描时均未发现错误。但是在对该表进行整体更新时，需要在扫描weather表的过程中对该表进行不断的更新操作。但是发现每次更新到第100条数据的时候就报scan的超时错误。即使只更新一行数据中的某一列也是如此（只获取区块首的时候扫描量会大大下降），于是证明不是扫描量的问题。具体报错如下

Exception in thread "main" java.lang.RuntimeException: org.apache.hadoop.hbase.client.ScannerTimeoutException: 1255382ms passed since the last invocation, timeout is currently set to 60000
    at org.apache.hadoop.hbase.client.AbstractClientScanner$1.hasNext(AbstractClientScanner.java:97)
    at com.zxc.fox.dao.IndexDao.updateAll(IndexDao.java:118)
    at com.zxc.fox.dao.IndexDao.main(IndexDao.java:38)
Caused by: org.apache.hadoop.hbase.client.ScannerTimeoutException: 1255382ms passed since the last invocation, timeout is currently set to 60000
    at org.apache.hadoop.hbase.client.ClientScanner.loadCache(ClientScanner.java:417)
    at org.apache.hadoop.hbase.client.ClientScanner.next(ClientScanner.java:332)
    at org.apache.hadoop.hbase.client.AbstractClientScanner$1.hasNext(AbstractClientScanner.java:94)
    ... 2 more
Caused by: org.apache.hadoop.hbase.UnknownScannerException: org.apache.hadoop.hbase.UnknownScannerException: Name: 533, already closed?
    at org.apache.hadoop.hbase.regionserver.RSRpcServices.scan(RSRpcServices.java:2017)
    at org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ClientService$2.callBlockingMethod(ClientProtos.java:31443)
    at org.apache.hadoop.hbase.ipc.RpcServer.call(RpcServer.java:2031)
    at org.apache.hadoop.hbase.ipc.CallRunner.run(CallRunner.java:107)
    at org.apache.hadoop.hbase.ipc.RpcExecutor.consumerLoop(RpcExecutor.java:130)
    at org.apache.hadoop.hbase.ipc.RpcExecutor$1.run(RpcExecutor.java:107)
    at java.lang.Thread.run(Thread.java:745)

    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:525)
    at org.apache.hadoop.ipc.RemoteException.instantiateException(RemoteException.java:106)
    at org.apache.hadoop.ipc.RemoteException.unwrapRemoteException(RemoteException.java:95)
    at org.apache.hadoop.hbase.protobuf.ProtobufUtil.getRemoteException(ProtobufUtil.java:313)
    at org.apache.hadoop.hbase.client.ScannerCallable.call(ScannerCallable.java:241)
    at org.apache.hadoop.hbase.client.ScannerCallable.call(ScannerCallable.java:62)
    at org.apache.hadoop.hbase.client.RpcRetryingCaller.callWithRetries(RpcRetryingCaller.java:126)
    at org.apache.hadoop.hbase.client.ScannerCallableWithReplicas$RetryingRPC.call(ScannerCallableWithReplicas.java:310)
    at org.apache.hadoop.hbase.client.ScannerCallableWithReplicas$RetryingRPC.call(ScannerCallableWithReplicas.java:291)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
    at java.util.concurrent.FutureTask.run(FutureTask.java:166)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:722)
Caused by: org.apache.hadoop.hbase.ipc.RemoteWithExtrasException(org.apache.hadoop.hbase.UnknownScannerException): org.apache.hadoop.hbase.UnknownScannerException: Name: 533, already closed?
    at org.apache.hadoop.hbase.regionserver.RSRpcServices.scan(RSRpcServices.java:2017)
    at org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ClientService$2.callBlockingMethod(ClientProtos.java:31443)
    at org.apache.hadoop.hbase.ipc.RpcServer.call(RpcServer.java:2031)
    at org.apache.hadoop.hbase.ipc.CallRunner.run(CallRunner.java:107)
    at org.apache.hadoop.hbase.ipc.RpcExecutor.consumerLoop(RpcExecutor.java:130)
    at org.apache.hadoop.hbase.ipc.RpcExecutor$1.run(RpcExecutor.java:107)
    at java.lang.Thread.run(Thread.java:745)

    at org.apache.hadoop.hbase.ipc.RpcClientImpl.call(RpcClientImpl.java:1199)
    at org.apache.hadoop.hbase.ipc.AbstractRpcClient.callBlockingMethod(AbstractRpcClient.java:216)
    at org.apache.hadoop.hbase.ipc.AbstractRpcClient$BlockingRpcChannelImplementation.callBlockingMethod(AbstractRpcClient.java:300)
    at org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ClientService$BlockingStub.scan(ClientProtos.java:31889)
    at org.apache.hadoop.hbase.client.ScannerCallable.call(ScannerCallable.java:200)
    ... 9 more

【解决过程】

　　先查看了datanode的错误日志，然后参考了如下两篇博客：参考博客01，参考博客02，在代码中配置了超时时间，未成功。修改了hadoop配置文件，但是没有起作用。仔细思考了问题出错的原因，比对了之前自己写的一些方法，最后发现我嵌套了两个scan，于是修改此部分代码，先用一个scan得到所有的城市id之后保存在一个list里，在遍历这个list来代替之前的scan，这样做在实践中没有出现明显的时间消耗，但是却避免了scan超时问题。

【体会】

　　出现该问题可能是由多种原因造成的，先检查一下。可以从如下几方面考虑

1. 是否你自己每次的scan处理较耗时？ ->  优化处理程序，scan一些设置调优（比如setBlockCache(false) ）

2. 是否每次scan的caching设置过大？  ->  减少caching （一般默认先设100）

3. 是否是网络或机器负载问题？    ->  查看集群原因

4. 是否HBase本身负载问题？     ->   查看RegionServer日志