UnknownScannerException is thrown by the region server if a scanner request
(next or close) is called with either a bogus scanner id (unlikely since the
scanner id is hidden from the client application) or if the scanner's lease has
expired.
Every client request is given a lease by the region server. If the lease times
out, the region server thinks that the client has gone away and it can clean up
any resources being held for that request. Lease timeouts almost always occur
on operations related to scanners. If a scanner's lease times out,
UnknownScannerException will be thrown if the client issues a scanner request
after the timeout because the region server has already cleaned up the
resources associated with the scanner. (The default lease timeout for client
requests is 30 seconds, so it is very likely that this is the situation you are
running into).
If you attempt to do an update to the same table that you have a scanner open
on, the update will stall waiting for the scanner to complete. So a loop which
does
while (scanner.next(key, val)) {
if (key.equals(something) || val.equals(somethingElse)) {
table.startUpdate(...)
table.put(...)
table.commit(...)
}
}
will not work because the update will wait for the scanner to finish, (which it
won't), and both the update and the next scanner.next should both fail.
Hope that helps.
---
Jim Kellerman, Senior Engineer; Powerset
[EMAIL PROTECTED]
> -----Original Message-----
> From: Cedric Ho [mailto:[EMAIL PROTECTED]
> Sent: Thursday, October 25, 2007 7:58 PM
> To: hadoop-user@lucene.apache.org
> Subject: HBase UnknownScannerException
>
> Hi,
>
> I was trying HBase from the 0.15 branch. And was doing:
>
> HScannerInterface s = table.obtainScanner(...)
> while(s.next(key, val)) {
> ....
> }
>
> And encounter the following exception whenever I spent too
> much time in the while loop, (e.g. > 30 ~ 120 seconds). I am
> also doing insert in the same table in another process. But
> the records they are working on are definitely non-overlapping.
>
> org.apache.hadoop.ipc.RemoteException:
> org.apache.hadoop.hbase.UnknownScannerException: Name:
> -7220522571873774180
> at
> org.apache.hadoop.hbase.HRegionServer.next(HRegionServer.java:1075)
> at
> sun.reflect.GeneratedMethodAccessor19.invoke(Unknown Source)
> at
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMeth
> odAccessorImpl.java:25)
> at java.lang.reflect.Method.invoke(Method.java:585)
> at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:379)
> at org.apache.hadoop.ipc.Server$Handler.run(Server.java:596)
>
> at org.apache.hadoop.ipc.Client.call(Client.java:482)
> at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:184)
> at $Proxy1.next(Unknown Source)
> at
> org.apache.hadoop.hbase.HTable$ClientScanner.next(HTable.java:831)
> ...
>
> there are totally 6 machines:
> one running namenode, secondarynamenode, hbase master five
> running datanode, regionserver
>
>
> Cheers,
> Cedric
>
