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From Bryan Keller <brya...@gmail.com>
Subject Re: HBaseClient.call() hang
Date Mon, 17 Dec 2012 17:18:29 GMT
It seems there was a cascading effect. The regionservers were busy with scanning a table, which
resulted in some long GC's. The GC's were long enough to trigger the Zookeeper timeout on
at least one regionserver, which resulted in the regionserver shutting itself down. This then
caused the Object.wait() call which got stuck, and only exited after the very long RPC timeout.

I have done a fair amount of work optimizing the GCs, and I increased the regionserver timeouts,
which should help with the regionserver shutdowns. But if a regionserver does shut down for
some other reason, this will still result in the Object.wait() hang.

One approach might be to have the regionservers send back a keep-alive, or progress, message
during a scan, and that message would reset the RPC timer. The regionserver could do this
every x number of rows processed server-side. Then the RPC timeout could be something more
sensible rather than being set to the longest time it takes to scan a region.

HBASE-5416 looks useful, it will make scans faster, but the problem I'm encountering will
still be present, but perhaps I could set the RPC timeout a bit lower. HBASE-6313 might fix
the hang, in which case I could live with the longer RPC timeout setting.

On Dec 14, 2012, at 9:49 PM, Ted Yu <yuzhihong@gmail.com> wrote:

> Bryan:
> bq. My only thought would be to forego using filters
> Please keep using filters.
> I and Sergey are working on HBASE-5416: Improve performance of scans with
> some kind of filters
> This feature allows you to specify one column family as being essential.
> The other column family is only returned to client when essential column
> family matches. I wonder if this may be of help to you.
> You mentioned regionserver going down or being busy. I assume it was not
> often that regionserver(s) went down. For busy region server, did you try
> jstack'ing regionserver process ?
> Thanks
> On Fri, Dec 14, 2012 at 2:59 PM, Bryan Keller <bryanck@gmail.com> wrote:
>> I have encountered a problem with HBaseClient.call() hanging. This occurs
>> when one of my regionservers goes down while performing a table scan.
>> What exacerbates this problem is that the scan I am performing uses
>> filters, and the region size of the table is large (4gb). Because of this,
>> it can take several minutes for a row to be returned when calling
>> scanner.next(). Apparently there is no keep alive message being sent back
>> to the scanner while the region server is busy, so I had to increase the
>> hbase.rpc.timeout value to a large number (60 min), otherwise the next()
>> call will timeout waiting for the regionserver to send something back.
>> The result is that this HBaseClient.call() hang is made much worse,
>> because it won't time out for 60 minutes.
>> I have a couple of questions:
>> 1. Any thoughts on why the HBaseClient.call() is getting stuck? I noticed
>> that call.wait() is not using any timeout so it will wait indefinitely
>> until interrupted externally
>> 2. Is there a solution where I do not need to set hbase.rpc.timeout to a
>> very large number? My only thought would be to forego using filters and do
>> the filtering client side, which seems pretty inefficient
>> Here is a stack dump of the thread that was hung:
>> Thread 10609: (state = BLOCKED)
>> - java.lang.Object.wait(long) @bci=0 (Interpreted frame)
>> - java.lang.Object.wait() @bci=2, line=485 (Interpreted frame)
>> -
>> org.apache.hadoop.hbase.ipc.HBaseClient.call(org.apache.hadoop.io.Writable,
>> java.net.InetSocketAddress, java.lang.Class,
>> org.apache.hadoop.hbase.security.User, int) @bci=51, line=904 (Interpreted
>> frame)
>> -
>> org.apache.hadoop.hbase.ipc.WritableRpcEngine$Invoker.invoke(java.lang.Object,
>> java.lang.reflect.Method, java.lang.Object[]) @bci=52, line=150
>> (Interpreted frame)
>> - $Proxy12.next(long, int) @bci=26 (Interpreted frame)
>> - org.apache.hadoop.hbase.client.ScannerCallable.call() @bci=72, line=92
>> (Interpreted frame)
>> - org.apache.hadoop.hbase.client.ScannerCallable.call() @bci=1, line=42
>> (Interpreted frame)
>> -
>> org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation.getRegionServerWithRetries(org.apache.hadoop.hbase.client.ServerCallable)
>> @bci=36, line=1325 (Interpreted frame)
>> - org.apache.hadoop.hbase.client.HTable$ClientScanner.next() @bci=117,
>> line=1299 (Compiled frame)
>> - org.apache.hadoop.hbase.mapreduce.TableRecordReaderImpl.nextKeyValue()
>> @bci=41, line=150 (Interpreted frame)
>> - org.apache.hadoop.hbase.mapreduce.TableRecordReader.nextKeyValue()
>> @bci=4, line=142 (Interpreted frame)
>> - org.apache.hadoop.mapred.MapTask$NewTrackingRecordReader.nextKeyValue()
>> @bci=4, line=458 (Interpreted frame)
>> - org.apache.hadoop.mapreduce.task.MapContextImpl.nextKeyValue() @bci=4,
>> line=76 (Interpreted frame)
>> -
>> org.apache.hadoop.mapreduce.lib.map.WrappedMapper$Context.nextKeyValue()
>> @bci=4, line=85 (Interpreted frame)
>> -
>> org.apache.hadoop.mapreduce.Mapper.run(org.apache.hadoop.mapreduce.Mapper$Context)
>> @bci=6, line=139 (Interpreted frame)
>> -
>> org.apache.hadoop.mapred.MapTask.runNewMapper(org.apache.hadoop.mapred.JobConf,
>> org.apache.hadoop.mapreduce.split.JobSplit$TaskSplitIndex,
>> org.apache.hadoop.mapred.TaskUmbilicalProtocol,
>> org.apache.hadoop.mapred.Task$TaskReporter) @bci=201, line=645 (Interpreted
>> frame)
>> - org.apache.hadoop.mapred.MapTask.run(org.apache.hadoop.mapred.JobConf,
>> org.apache.hadoop.mapred.TaskUmbilicalProtocol) @bci=100, line=325
>> (Interpreted frame)
>> - org.apache.hadoop.mapred.Child$4.run() @bci=29, line=268 (Interpreted
>> frame)
>> -
>> java.security.AccessController.doPrivileged(java.security.PrivilegedExceptionAction,
>> java.security.AccessControlContext) @bci=0 (Interpreted frame)
>> - javax.security.auth.Subject.doAs(javax.security.auth.Subject,
>> java.security.PrivilegedExceptionAction) @bci=42, line=396 (Interpreted
>> frame)
>> -
>> org.apache.hadoop.security.UserGroupInformation.doAs(java.security.PrivilegedExceptionAction)
>> @bci=14, line=1332 (Interpreted frame)
>> - org.apache.hadoop.mapred.Child.main(java.lang.String[]) @bci=776,
>> line=262 (Interpreted frame)

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