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https://issues.apache.org/jira/browse/HBASE-9821?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13802532#comment-13802532
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Jimmy Xiang commented on HBASE-9821:
------------------------------------
The start code is used to differentiate the region server instances started on
the same host, port. On different servers, if the start code is the same, it's
fine. The scanner should not use the one id for a server running on a different
box.
> Scanner id could collide
> ------------------------
>
> Key: HBASE-9821
> URL: https://issues.apache.org/jira/browse/HBASE-9821
> Project: HBase
> Issue Type: Bug
> Reporter: Jimmy Xiang
> Assignee: Jimmy Xiang
> Priority: Minor
>
> We use a random number as our scanner id. In one server, we guarantee that
> the scanner id is unique. However, it is not guaranteed among different
> servers. When a region server restarts quickly, we could run into some
> scanner id collision issue.
> In one of my run:
> {noformat}
> 2013-10-21 22:43:09,071 INFO [RpcServer.handler=2,port=36020]
> regionserver.HRegionServer: Client tried to access missing scanner
> 4305495321392639779
> 2013-10-21 22:43:09,056 INFO [RpcServer.handler=0,port=36020]
> regionserver.HRegionServer: Client tried to access missing scanner
> 4871518173034616791
> 2013-10-21 22:43:09,054 INFO [RpcServer.handler=29,port=36020]
> regionserver.HRegionServer: Client tried to access missing scanner
> 2494346173615963501
> 2013-10-21 22:43:09,046 INFO [RpcServer.handler=28,port=36020]
> regionserver.HRegionServer: Client tried to access missing scanner
> 8522578499834310167
> 2013-10-21 22:43:09,037 INFO [RpcServer.handler=27,port=36020]
> regionserver.HRegionServer: Client tried to access missing scanner
> 6621035169671703961
> 2013-10-21 22:43:09,011 ERROR [RpcServer.handler=20,port=36020]
> regionserver.HRegionServer:
> org.apache.hadoop.hbase.exceptions.OutOfOrderScannerNextException: Expected
> nextCallSeq: 18 But the nextCallSeq got from client: 4470;
> request=scanner_id: 848804760654927372 number_of_rows: 100 close_scanner:
> false next_call_seq: 4470
> at
> org.apache.hadoop.hbase.regionserver.HRegionServer.scan(HRegionServer.java:3030)
> at
> org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ClientService$2.callBlockingMethod(ClientProtos.java:27022)
> at org.apache.hadoop.hbase.ipc.RpcServer.call(RpcServer.java:1979)
> at org.apache.hadoop.hbase.ipc.CallRunner.run(CallRunner.java:90)
> at
> org.apache.hadoop.hbase.ipc.SimpleRpcScheduler.consumerLoop(SimpleRpcScheduler.java:160)
> at
> org.apache.hadoop.hbase.ipc.SimpleRpcScheduler.access$000(SimpleRpcScheduler.java:38)
> at
> org.apache.hadoop.hbase.ipc.SimpleRpcScheduler$1.run(SimpleRpcScheduler.java:110)
> at java.lang.Thread.run(Thread.java:724)
> 2013-10-21 22:43:09,000 INFO [RpcServer.handler=25,port=36020]
> regionserver.HRegionServer: Client tried to access missing scanner
> 4162107982028594792
> {noformat}
> Normally, the nextCallSeq can not be that different between the expected (18)
> and the one sent over from client (4470). It must be because the new server
> happens to use the same scanner id.
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