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From "ramkrishna.s.vasudevan (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (HBASE-16604) Scanner retries on IOException can cause the scans to miss data
Date Mon, 26 Sep 2016 08:42:21 GMT

    [ https://issues.apache.org/jira/browse/HBASE-16604?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15522451#comment-15522451
] 

ramkrishna.s.vasudevan edited comment on HBASE-16604 at 9/26/16 8:41 AM:
-------------------------------------------------------------------------

[~enis]
Due to recent failure in master branch test cases I had to check this fix. Few questions on
the fix. Pls do correct me if I was wrong.
{code}
  // The scanner state might be left in a dirty state, so we will tell the Client to
          // fail this RPC and close the scanner while opening up another one from the start
of
          // row that the client has last seen.
          closeScanner(region, scanner, scannerName, context);

          // We closed the scanner already. Instead of throwing the IOException, and client
          // retrying with the same scannerId only to get USE on the next RPC, we directly
throw
          // a special exception to save an RPC.
          if (VersionInfoUtil.hasMinimumVersion(context.getClientVersionInfo(), 1, 4)) {
            // 1.4.0+ clients know how to handle
            throw new ScannerResetException("Scanner is closed on the server-side", e);
          } else {
            // older clients do not know about SRE. Just throw USE, which they will handle
            throw new UnknownScannerException("Throwing UnknownScannerException to reset the
client"
                + " scanner state for clients older than 1.3.", e);
          }
{code}
So in the catch block first closeScanner happens and then a ScannerresetException of type
DNRE is thrown. 
Inside closeScanner we first remove the scanner from the scanner's map and then cancel the
lease also. (the lease is removed from the lease holder).
Now the client on seeing this exception will try to retry this Exception. Since the scanner
is removed from the scanner's map and already we have a scannerId associated with the scan
request,
{code}
if (request.hasScannerId()) {
        rsh = scanners.get(scannerName);
        if (rsh == null) {
          LOG.warn("Client tried to access missing scanner " + scannerName);
          throw new UnknownScannerException(
            "Unknown scanner '" + scannerName + "'. This can happen due to any of the following
"
                + "reasons: a) Scanner id given is wrong, b) Scanner lease expired because
of "
                + "long wait between consecutive client checkins, c) Server may be closing
down, "
                + "d) RegionServer restart during upgrade.\nIf the issue is due to reason
(b), a "
                + "possible fix would be increasing the value of"
                + "'hbase.client.scanner.timeout.period' configuration.");
        }
{code}
Will not the subsequent retry also fail? 
The other problem here is that since the above catch block is immediately followed by a finally
block
{code}
finally {
          if (context != null) {
            context.setCallBack(rsh.shippedCallback);
          }
          // Adding resets expiration time on lease.
          if (scanners.containsKey(scannerName)) {
            ttl = this.scannerLeaseTimeoutPeriod;
            // When context != null, adding back the lease will be done in callback set above.
            if (context == null) {
              if (lease != null) regionServer.leases.addLease(lease);
            }
          }
        }
{code}
the rpcCallback (when context  !=null) is set with the shippedCallback. Now even before this
since the patch tries to close the scanner the scanner is removed from the scanner map and
hence the RegionScannerShippedCallBack#run() will not be able to add the lease back and hence
because of this the LeaseExpiry listener does not do the necessary clean up and hence the
block eviction also fails. 
So the 2nd part of the problem is what I was checking and I found the first part also to have
some problem which I may be wrong.

Now we have 2 things I think,
->In case of actual retries whether the scanner internals and its heap are reset properly
-> In case my retries are over how am I cleaning up the heap and also the blocks. This
will happen only for master branch I think and we need to fix only in 2.0.
Thanks [~enis].


was (Author: ram_krish):
[~enis]
Due to recent failure in master branch test cases I had to check this fix. Few questions on
the fix. Pls do correct me if I was wrong.
{code}
{code}

> Scanner retries on IOException can cause the scans to miss data 
> ----------------------------------------------------------------
>
>                 Key: HBASE-16604
>                 URL: https://issues.apache.org/jira/browse/HBASE-16604
>             Project: HBase
>          Issue Type: Bug
>          Components: regionserver, Scanners
>            Reporter: Enis Soztutar
>            Assignee: Enis Soztutar
>             Fix For: 2.0.0, 1.3.0, 1.4.0, 1.1.7, 1.2.4
>
>         Attachments: HBASE-16604-branch-1.3-addendum.patch, hbase-16604_v1.patch, hbase-16604_v2.patch,
hbase-16604_v3.branch-1.patch, hbase-16604_v3.patch
>
>
> Debugging an ITBLL failure, where the Verify did not "see" all the data in the cluster,
I've noticed that if we end up getting a generic IOException from the HFileReader level, we
may end up missing the rest of the data in the region. I was able to manually test this, and
this stack trace helps to understand what is going on: 
> {code}
> 2016-09-09 16:27:15,633 INFO  [hconnection-0x71ad3d8a-shared--pool21-t9] client.ScannerCallable(376):
Open scanner=1 for scan={"loadColumnFamiliesOnDemand":null,"startRow":"","stopRow":"","batch":-1,"cacheBlocks":true,"totalColumns":1,"maxResultSize":2097152,"families":{"testFamily":["testFamily"]},"caching":100,"maxVersions":1,"timeRange":[0,9223372036854775807]}
on region region=testScanThrowsException,,1473463632707.b2adfb618e5d0fe225c1dc40c0eabfee.,
hostname=hw10676,51833,1473463626529, seqNum=2
> 2016-09-09 16:27:15,634 INFO  [B.fifo.QRpcServer.handler=5,queue=0,port=51833] regionserver.RSRpcServices(2196):
scan request:scanner_id: 1 number_of_rows: 100 close_scanner: false next_call_seq: 0 client_handles_partials:
true client_handles_heartbeats: true renew: false
> 2016-09-09 16:27:15,635 INFO  [B.fifo.QRpcServer.handler=5,queue=0,port=51833] regionserver.RSRpcServices(2510):
Rolling back next call seqId
> 2016-09-09 16:27:15,635 INFO  [B.fifo.QRpcServer.handler=5,queue=0,port=51833] regionserver.RSRpcServices(2565):
Throwing new ServiceExceptionjava.io.IOException: Could not reseek StoreFileScanner[HFileScanner
for reader reader=hdfs://localhost:51795/user/enis/test-data/d6fb1c70-93c1-4099-acb7-5723fc05a737/data/default/testScanThrowsException/b2adfb618e5d0fe225c1dc40c0eabfee/testFamily/5a213cc23b714e5e8e1a140ebbe72f2c,
compression=none, cacheConf=blockCache=LruBlockCache{blockCount=0, currentSize=1567264, freeSize=1525578848,
maxSize=1527146112, heapSize=1567264, minSize=1450788736, minFactor=0.95, multiSize=725394368,
multiFactor=0.5, singleSize=362697184, singleFactor=0.25}, cacheDataOnRead=true, cacheDataOnWrite=false,
cacheIndexesOnWrite=false, cacheBloomsOnWrite=false, cacheEvictOnClose=false, cacheDataCompressed=false,
prefetchOnOpen=false, firstKey=aaa/testFamily:testFamily/1473463633859/Put, lastKey=zzz/testFamily:testFamily/1473463634271/Put,
avgKeyLen=35, avgValueLen=3, entries=17576, length=866998, cur=/testFamily:/OLDEST_TIMESTAMP/Minimum/vlen=0/seqid=0]
to key /testFamily:testFamily/LATEST_TIMESTAMP/Maximum/vlen=0/seqid=0
> 2016-09-09 16:27:15,635 DEBUG [B.fifo.QRpcServer.handler=5,queue=0,port=51833] ipc.CallRunner(110):
B.fifo.QRpcServer.handler=5,queue=0,port=51833: callId: 26 service: ClientService methodName:
Scan size: 26 connection: 192.168.42.75:51903
> java.io.IOException: Could not reseek StoreFileScanner[HFileScanner for reader reader=hdfs://localhost:51795/user/enis/test-data/d6fb1c70-93c1-4099-acb7-5723fc05a737/data/default/testScanThrowsException/b2adfb618e5d0fe225c1dc40c0eabfee/testFamily/5a213cc23b714e5e8e1a140ebbe72f2c,
compression=none, cacheConf=blockCache=LruBlockCache{blockCount=0, currentSize=1567264, freeSize=1525578848,
maxSize=1527146112, heapSize=1567264, minSize=1450788736, minFactor=0.95, multiSize=725394368,
multiFactor=0.5, singleSize=362697184, singleFactor=0.25}, cacheDataOnRead=true, cacheDataOnWrite=false,
cacheIndexesOnWrite=false, cacheBloomsOnWrite=false, cacheEvictOnClose=false, cacheDataCompressed=false,
prefetchOnOpen=false, firstKey=aaa/testFamily:testFamily/1473463633859/Put, lastKey=zzz/testFamily:testFamily/1473463634271/Put,
avgKeyLen=35, avgValueLen=3, entries=17576, length=866998, cur=/testFamily:/OLDEST_TIMESTAMP/Minimum/vlen=0/seqid=0]
to key /testFamily:testFamily/LATEST_TIMESTAMP/Maximum/vlen=0/seqid=0
> 	at org.apache.hadoop.hbase.regionserver.StoreFileScanner.reseek(StoreFileScanner.java:224)
> 	at org.apache.hadoop.hbase.regionserver.NonLazyKeyValueScanner.doRealSeek(NonLazyKeyValueScanner.java:55)
> 	at org.apache.hadoop.hbase.regionserver.KeyValueHeap.generalizedSeek(KeyValueHeap.java:312)
> 	at org.apache.hadoop.hbase.regionserver.KeyValueHeap.requestSeek(KeyValueHeap.java:268)
> 	at org.apache.hadoop.hbase.regionserver.StoreScanner.reseek(StoreScanner.java:815)
> 	at org.apache.hadoop.hbase.regionserver.StoreScanner.seekAsDirection(StoreScanner.java:803)
> 	at org.apache.hadoop.hbase.regionserver.StoreScanner.next(StoreScanner.java:625)
> 	at org.apache.hadoop.hbase.regionserver.KeyValueHeap.next(KeyValueHeap.java:147)
> 	at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.populateResult(HRegion.java:5736)
> 	at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.nextInternal(HRegion.java:5887)
> 	at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.nextRaw(HRegion.java:5674)
> 	at org.apache.hadoop.hbase.regionserver.RSRpcServices.scan(RSRpcServices.java:2434)
> 	at org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ClientService$2.callBlockingMethod(ClientProtos.java:32295)
> 	at org.apache.hadoop.hbase.ipc.RpcServer.call(RpcServer.java:2127)
> 	at org.apache.hadoop.hbase.ipc.CallRunner.run(CallRunner.java:107)
> 	at org.apache.hadoop.hbase.ipc.RpcExecutor.consumerLoop(RpcExecutor.java:133)
> 	at org.apache.hadoop.hbase.ipc.RpcExecutor$2.run(RpcExecutor.java:108)
> 	at java.lang.Thread.run(Thread.java:745)
> Caused by: java.io.IOException: foo bar baz
> 	at org.apache.hadoop.hbase.regionserver.StoreFileScanner.reseek(StoreFileScanner.java:207)
> 	... 17 more
> 2016-09-09 16:27:15,653 INFO  [hconnection-0x71ad3d8a-shared--pool21-t10] client.ScannerCallable(261):
Got exception making request scanner_id: 1 number_of_rows: 100 close_scanner: false next_call_seq:
0 client_handles_partials: true client_handles_heartbeats: true renew: false to region=testScanThrowsException,,1473463632707.b2adfb618e5d0fe225c1dc40c0eabfee.,
hostname=hw10676,51833,1473463626529, seqNum=2
> java.io.IOException: java.io.IOException: Could not reseek StoreFileScanner[HFileScanner
for reader reader=hdfs://localhost:51795/user/enis/test-data/d6fb1c70-93c1-4099-acb7-5723fc05a737/data/default/testScanThrowsException/b2adfb618e5d0fe225c1dc40c0eabfee/testFamily/5a213cc23b714e5e8e1a140ebbe72f2c,
compression=none, cacheConf=blockCache=LruBlockCache{blockCount=0, currentSize=1567264, freeSize=1525578848,
maxSize=1527146112, heapSize=1567264, minSize=1450788736, minFactor=0.95, multiSize=725394368,
multiFactor=0.5, singleSize=362697184, singleFactor=0.25}, cacheDataOnRead=true, cacheDataOnWrite=false,
cacheIndexesOnWrite=false, cacheBloomsOnWrite=false, cacheEvictOnClose=false, cacheDataCompressed=false,
prefetchOnOpen=false, firstKey=aaa/testFamily:testFamily/1473463633859/Put, lastKey=zzz/testFamily:testFamily/1473463634271/Put,
avgKeyLen=35, avgValueLen=3, entries=17576, length=866998, cur=/testFamily:/OLDEST_TIMESTAMP/Minimum/vlen=0/seqid=0]
to key /testFamily:testFamily/LATEST_TIMESTAMP/Maximum/vlen=0/seqid=0
> 	at org.apache.hadoop.hbase.regionserver.StoreFileScanner.reseek(StoreFileScanner.java:224)
> 	at org.apache.hadoop.hbase.regionserver.NonLazyKeyValueScanner.doRealSeek(NonLazyKeyValueScanner.java:55)
> 	at org.apache.hadoop.hbase.regionserver.KeyValueHeap.generalizedSeek(KeyValueHeap.java:312)
> 	at org.apache.hadoop.hbase.regionserver.KeyValueHeap.requestSeek(KeyValueHeap.java:268)
> 	at org.apache.hadoop.hbase.regionserver.StoreScanner.reseek(StoreScanner.java:815)
> 	at org.apache.hadoop.hbase.regionserver.StoreScanner.seekAsDirection(StoreScanner.java:803)
> 	at org.apache.hadoop.hbase.regionserver.StoreScanner.next(StoreScanner.java:625)
> 	at org.apache.hadoop.hbase.regionserver.KeyValueHeap.next(KeyValueHeap.java:147)
> 	at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.populateResult(HRegion.java:5736)
> 	at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.nextInternal(HRegion.java:5887)
> 	at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.nextRaw(HRegion.java:5674)
> 	at org.apache.hadoop.hbase.regionserver.RSRpcServices.scan(RSRpcServices.java:2434)
> 	at org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ClientService$2.callBlockingMethod(ClientProtos.java:32295)
> 	at org.apache.hadoop.hbase.ipc.RpcServer.call(RpcServer.java:2127)
> 	at org.apache.hadoop.hbase.ipc.CallRunner.run(CallRunner.java:107)
> 	at org.apache.hadoop.hbase.ipc.RpcExecutor.consumerLoop(RpcExecutor.java:133)
> 	at org.apache.hadoop.hbase.ipc.RpcExecutor$2.run(RpcExecutor.java:108)
> 	at java.lang.Thread.run(Thread.java:745)
> Caused by: java.io.IOException: foo bar baz
> 	at org.apache.hadoop.hbase.regionserver.StoreFileScanner.reseek(StoreFileScanner.java:207)
> 	... 17 more
> 	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
> 	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
> 	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
> 	at java.lang.reflect.Constructor.newInstance(Constructor.java:422)
> 	at org.apache.hadoop.ipc.RemoteException.instantiateException(RemoteException.java:106)
> 	at org.apache.hadoop.ipc.RemoteException.unwrapRemoteException(RemoteException.java:95)
> 	at org.apache.hadoop.hbase.protobuf.ProtobufUtil.getRemoteException(ProtobufUtil.java:332)
> 	at org.apache.hadoop.hbase.client.ScannerCallable.call(ScannerCallable.java:256)
> 	at org.apache.hadoop.hbase.client.ScannerCallable.call(ScannerCallable.java:1)
> 	at org.apache.hadoop.hbase.client.RpcRetryingCaller.callWithoutRetries(RpcRetryingCaller.java:200)
> 	at org.apache.hadoop.hbase.client.ScannerCallableWithReplicas$RetryingRPC.call(ScannerCallableWithReplicas.java:364)
> 	at org.apache.hadoop.hbase.client.ScannerCallableWithReplicas$RetryingRPC.call(ScannerCallableWithReplicas.java:1)
> 	at org.apache.hadoop.hbase.client.RpcRetryingCaller.callWithRetries(RpcRetryingCaller.java:126)
> 	at org.apache.hadoop.hbase.client.ResultBoundedCompletionService$QueueingFuture.run(ResultBoundedCompletionService.java:65)
> 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
> 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
> 	at java.lang.Thread.run(Thread.java:745)
> Caused by: org.apache.hadoop.hbase.ipc.RemoteWithExtrasException(java.io.IOException):
java.io.IOException: Could not reseek StoreFileScanner[HFileScanner for reader reader=hdfs://localhost:51795/user/enis/test-data/d6fb1c70-93c1-4099-acb7-5723fc05a737/data/default/testScanThrowsException/b2adfb618e5d0fe225c1dc40c0eabfee/testFamily/5a213cc23b714e5e8e1a140ebbe72f2c,
compression=none, cacheConf=blockCache=LruBlockCache{blockCount=0, currentSize=1567264, freeSize=1525578848,
maxSize=1527146112, heapSize=1567264, minSize=1450788736, minFactor=0.95, multiSize=725394368,
multiFactor=0.5, singleSize=362697184, singleFactor=0.25}, cacheDataOnRead=true, cacheDataOnWrite=false,
cacheIndexesOnWrite=false, cacheBloomsOnWrite=false, cacheEvictOnClose=false, cacheDataCompressed=false,
prefetchOnOpen=false, firstKey=aaa/testFamily:testFamily/1473463633859/Put, lastKey=zzz/testFamily:testFamily/1473463634271/Put,
avgKeyLen=35, avgValueLen=3, entries=17576, length=866998, cur=/testFamily:/OLDEST_TIMESTAMP/Minimum/vlen=0/seqid=0]
to key /testFamily:testFamily/LATEST_TIMESTAMP/Maximum/vlen=0/seqid=0
> 	at org.apache.hadoop.hbase.regionserver.StoreFileScanner.reseek(StoreFileScanner.java:224)
> 	at org.apache.hadoop.hbase.regionserver.NonLazyKeyValueScanner.doRealSeek(NonLazyKeyValueScanner.java:55)
> 	at org.apache.hadoop.hbase.regionserver.KeyValueHeap.generalizedSeek(KeyValueHeap.java:312)
> 	at org.apache.hadoop.hbase.regionserver.KeyValueHeap.requestSeek(KeyValueHeap.java:268)
> 	at org.apache.hadoop.hbase.regionserver.StoreScanner.reseek(StoreScanner.java:815)
> 	at org.apache.hadoop.hbase.regionserver.StoreScanner.seekAsDirection(StoreScanner.java:803)
> 	at org.apache.hadoop.hbase.regionserver.StoreScanner.next(StoreScanner.java:625)
> 	at org.apache.hadoop.hbase.regionserver.KeyValueHeap.next(KeyValueHeap.java:147)
> 	at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.populateResult(HRegion.java:5736)
> 	at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.nextInternal(HRegion.java:5887)
> 	at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.nextRaw(HRegion.java:5674)
> 	at org.apache.hadoop.hbase.regionserver.RSRpcServices.scan(RSRpcServices.java:2434)
> 	at org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ClientService$2.callBlockingMethod(ClientProtos.java:32295)
> 	at org.apache.hadoop.hbase.ipc.RpcServer.call(RpcServer.java:2127)
> 	at org.apache.hadoop.hbase.ipc.CallRunner.run(CallRunner.java:107)
> 	at org.apache.hadoop.hbase.ipc.RpcExecutor.consumerLoop(RpcExecutor.java:133)
> 	at org.apache.hadoop.hbase.ipc.RpcExecutor$2.run(RpcExecutor.java:108)
> 	at java.lang.Thread.run(Thread.java:745)
> Caused by: java.io.IOException: foo bar baz
> 	at org.apache.hadoop.hbase.regionserver.StoreFileScanner.reseek(StoreFileScanner.java:207)
> 	... 17 more
> 	at org.apache.hadoop.hbase.ipc.RpcClientImpl.call(RpcClientImpl.java:1225)
> 	at org.apache.hadoop.hbase.ipc.AbstractRpcClient.callBlockingMethod(AbstractRpcClient.java:213)
> 	at org.apache.hadoop.hbase.ipc.AbstractRpcClient$BlockingRpcChannelImplementation.callBlockingMethod(AbstractRpcClient.java:287)
> 	at org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ClientService$BlockingStub.scan(ClientProtos.java:32741)
> 	at org.apache.hadoop.hbase.client.ScannerCallable.call(ScannerCallable.java:214)
> 	... 9 more
> 2016-09-09 16:27:15,963 INFO  [B.priority.fifo.QRpcServer.handler=8,queue=0,port=51824]
regionserver.RSRpcServices(2196): scan request:region { type: REGION_NAME value: "hbase:meta,,1"
} scan { start_row: "testScanThrowsException,,99999999999999" max_versions: 1 cache_blocks:
true small: true reversed: true caching: 1 } number_of_rows: 1 close_scanner: true client_handles_partials:
true client_handles_heartbeats: true
> 2016-09-09 16:27:15,965 INFO  [B.priority.fifo.QRpcServer.handler=8,queue=0,port=51824]
regionserver.RSRpcServices(2549): class org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ScanResponse:cells_per_result:
4 scanner_id: 15 more_results: false stale: false partial_flag_per_result: false more_results_in_region:
true heartbeat_message: false
> 2016-09-09 16:27:15,967 INFO  [B.fifo.QRpcServer.handler=0,queue=0,port=51833] regionserver.RSRpcServices(2196):
scan request:scanner_id: 1 number_of_rows: 100 close_scanner: false next_call_seq: 0 client_handles_partials:
true client_handles_heartbeats: true renew: false
> 2016-09-09 16:27:15,967 INFO  [B.fifo.QRpcServer.handler=0,queue=0,port=51833] regionserver.RSRpcServices(2549):
class org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ScanResponse:scanner_id: 1 more_results:
true ttl: 60000 stale: false more_results_in_region: false
> 2016-09-09 16:27:15,968 INFO  [B.fifo.QRpcServer.handler=1,queue=0,port=51833] regionserver.RSRpcServices(2196):
scan request:scanner_id: 1 number_of_rows: 0 close_scanner: true client_handles_partials:
true client_handles_heartbeats: true
> 2016-09-09 16:27:15,968 INFO  [B.fifo.QRpcServer.handler=1,queue=0,port=51833] regionserver.RSRpcServices(2549):
class org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ScanResponse:scanner_id: 1 more_results:
false
> 2016-09-09 16:27:15,971 INFO  [main] hbase.HBaseTestingUtility(1111): Shutting down minicluster
> {code}
> The ScannerCallable is retryable if it gets a IOException. Before the HBASE-13662 fix,
the retry was still failing due to OutOfOrderScannerException, which then causes the Scanner
stack to be reset, thus masking the issue. After HBASE-13662, we can retry the same scan,
but in case of we are doing a {{reseek()}} which fails in middle with an IOException, the
KVHeaps and the Scanner state on the server side is left dirty. 
> It seems to be much safer to reset the scanner state in case of IOExceptions. 



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