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From John Leach <jle...@splicemachine.com>
Subject Re: Hot Region Server With No Hot Region
Date Fri, 02 Dec 2016 19:34:45 GMT
Here is what I see...


* Short Compaction Running on Heap
"regionserver/ip-10-99-181-146.aolp-prd.us-east-1.ec2.aolcloud.net/10.99.181.146:60020-shortCompactions-1480229281547"
- Thread t@242
   java.lang.Thread.State: RUNNABLE
    at org.apache.hadoop.hbase.io.encoding.FastDiffDeltaEncoder.compressSingleKeyValue(FastDiffDeltaEncoder.java:270)
    at org.apache.hadoop.hbase.io.encoding.FastDiffDeltaEncoder.internalEncode(FastDiffDeltaEncoder.java:245)
    at org.apache.hadoop.hbase.io.encoding.BufferedDataBlockEncoder.encode(BufferedDataBlockEncoder.java:987)
    at org.apache.hadoop.hbase.io.encoding.FastDiffDeltaEncoder.encode(FastDiffDeltaEncoder.java:58)
    at org.apache.hadoop.hbase.io.hfile.HFileDataBlockEncoderImpl.encode(HFileDataBlockEncoderImpl.java:97)
    at org.apache.hadoop.hbase.io.hfile.HFileBlock$Writer.write(HFileBlock.java:866)
    at org.apache.hadoop.hbase.io.hfile.HFileWriterV2.append(HFileWriterV2.java:270)
    at org.apache.hadoop.hbase.io.hfile.HFileWriterV3.append(HFileWriterV3.java:87)
    at org.apache.hadoop.hbase.regionserver.StoreFile$Writer.append(StoreFile.java:949)
    at org.apache.hadoop.hbase.regionserver.compactions.Compactor.performCompaction(Compactor.java:282)
    at org.apache.hadoop.hbase.regionserver.compactions.DefaultCompactor.compact(DefaultCompactor.java:105)
    at org.apache.hadoop.hbase.regionserver.DefaultStoreEngine$DefaultCompactionContext.compact(DefaultStoreEngine.java:124)
    at org.apache.hadoop.hbase.regionserver.HStore.compact(HStore.java:1233)
    at org.apache.hadoop.hbase.regionserver.HRegion.compact(HRegion.java:1770)
    at org.apache.hadoop.hbase.regionserver.CompactSplitThread$CompactionRunner.run(CompactSplitThread.java:520)
    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)


* WAL Syncs waiting…   ALL 5
"sync.0" - Thread t@202
   java.lang.Thread.State: TIMED_WAITING
    at java.lang.Object.wait(Native Method)
    - waiting on <67ba892d> (a java.util.LinkedList)
    at org.apache.hadoop.hdfs.DFSOutputStream.waitForAckedSeqno(DFSOutputStream.java:2337)
    at org.apache.hadoop.hdfs.DFSOutputStream.flushOrSync(DFSOutputStream.java:2224)
    at org.apache.hadoop.hdfs.DFSOutputStream.hflush(DFSOutputStream.java:2116)
    at org.apache.hadoop.fs.FSDataOutputStream.hflush(FSDataOutputStream.java:130)
    at org.apache.hadoop.hbase.regionserver.wal.ProtobufLogWriter.sync(ProtobufLogWriter.java:173)
    at org.apache.hadoop.hbase.regionserver.wal.FSHLog$SyncRunner.run(FSHLog.java:1379)
    at java.lang.Thread.run(Thread.java:745)

* Mutations backing up very badly...

"B.defaultRpcServer.handler=103,queue=7,port=60020" - Thread t@155
   java.lang.Thread.State: TIMED_WAITING
    at java.lang.Object.wait(Native Method)
    - waiting on <6ab54ea3> (a org.apache.hadoop.hbase.regionserver.wal.SyncFuture)
    at org.apache.hadoop.hbase.regionserver.wal.SyncFuture.get(SyncFuture.java:167)
    at org.apache.hadoop.hbase.regionserver.wal.FSHLog.blockOnSync(FSHLog.java:1504)
    at org.apache.hadoop.hbase.regionserver.wal.FSHLog.publishSyncThenBlockOnCompletion(FSHLog.java:1498)
    at org.apache.hadoop.hbase.regionserver.wal.FSHLog.sync(FSHLog.java:1632)
    at org.apache.hadoop.hbase.regionserver.HRegion.syncOrDefer(HRegion.java:7737)
    at org.apache.hadoop.hbase.regionserver.HRegion.processRowsWithLocks(HRegion.java:6504)
    at org.apache.hadoop.hbase.regionserver.HRegion.mutateRowsWithLocks(HRegion.java:6352)
    at org.apache.hadoop.hbase.regionserver.HRegion.mutateRowsWithLocks(HRegion.java:6334)
    at org.apache.hadoop.hbase.regionserver.HRegion.mutateRow(HRegion.java:6325)
    at org.apache.hadoop.hbase.regionserver.RSRpcServices.mutateRows(RSRpcServices.java:418)
    at org.apache.hadoop.hbase.regionserver.RSRpcServices.multi(RSRpcServices.java:1916)
    at org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ClientService$2.callBlockingMethod(ClientProtos.java:32213)
    at org.apache.hadoop.hbase.ipc.RpcServer.call(RpcServer.java:2034)
    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)


Too many writers being blocked attempting to write to WAL.

What does your disk infrastructure look like?  Can you get away with Multi-wal?  Ugh...

Regards,
John Leach


> On Dec 2, 2016, at 1:20 PM, Saad Mufti <saad.mufti@gmail.com> wrote:
> 
> Hi Ted,
> 
> Finally we have another hotspot going on, same symptoms as before, here is
> the pastebin for the stack trace from the region server that I obtained via
> VisualVM:
> 
> http://pastebin.com/qbXPPrXk
> 
> Would really appreciate any insight you or anyone else can provide.
> 
> Thanks.
> 
> ----
> Saad
> 
> 
> On Thu, Dec 1, 2016 at 6:08 PM, Saad Mufti <saad.mufti@gmail.com> wrote:
> 
>> Sure will, the next time it happens.
>> 
>> Thanks!!!
>> 
>> ----
>> Saad
>> 
>> 
>> On Thu, Dec 1, 2016 at 5:01 PM, Ted Yu <ted_yu@yahoo.com.invalid> wrote:
>> 
>>> From #2 in the initial email, the hbase:meta might not be the cause for
>>> the hotspot.
>>> 
>>> Saad:
>>> Can you pastebin stack trace of the hot region server when this happens
>>> again ?
>>> 
>>> Thanks
>>> 
>>>> On Dec 2, 2016, at 4:48 AM, Saad Mufti <saad.mufti@gmail.com> wrote:
>>>> 
>>>> We used a pre-split into 1024 regions at the start but we miscalculated
>>> our
>>>> data size, so there were still auto-splits storms at the beginning as
>>> data
>>>> size stabilized, it has ended up at around 9500 or so regions, plus a
>>> few
>>>> thousand regions for a few other tables (much smaller). But haven't had
>>> any
>>>> new auto-splits in a couple of months. And the hotspots only started
>>>> happening recently.
>>>> 
>>>> Our hashing scheme is very simple, we take the MD5 of the key, then
>>> form a
>>>> 4 digit prefix based on the first two bytes of the MD5 normalized to be
>>>> within the range 0-1023 . I am fairly confident about this scheme
>>>> especially since even during the hotspot we see no evidence so far that
>>> any
>>>> particular region is taking disproportionate traffic (based on Cloudera
>>>> Manager per region charts on the hotspot server). Does that look like a
>>>> reasonable scheme to randomize which region any give key goes to? And
>>> the
>>>> start of the hotspot doesn't seem to correspond to any region splitting
>>> or
>>>> moving from one server to another activity.
>>>> 
>>>> Thanks.
>>>> 
>>>> ----
>>>> Saad
>>>> 
>>>> 
>>>>> On Thu, Dec 1, 2016 at 3:32 PM, John Leach <jleach@splicemachine.com>
>>> wrote:
>>>>> 
>>>>> Saad,
>>>>> 
>>>>> Region move or split causes client connections to simultaneously
>>> refresh
>>>>> their meta.
>>>>> 
>>>>> Key word is supposed.  We have seen meta hot spotting from time to time
>>>>> and on different versions at Splice Machine.
>>>>> 
>>>>> How confident are you in your hashing algorithm?
>>>>> 
>>>>> Regards,
>>>>> John Leach
>>>>> 
>>>>> 
>>>>> 
>>>>>> On Dec 1, 2016, at 2:25 PM, Saad Mufti <saad.mufti@gmail.com>
wrote:
>>>>>> 
>>>>>> No never thought about that. I just figured out how to locate the
>>> server
>>>>>> for that table after you mentioned it. We'll have to keep an eye
on it
>>>>> next
>>>>>> time we have a hotspot to see if it coincides with the hotspot server.
>>>>>> 
>>>>>> What would be the theory for how it could become a hotspot? Isn't
the
>>>>>> client supposed to cache it and only go back for a refresh if it
hits
>>> a
>>>>>> region that is not in its expected location?
>>>>>> 
>>>>>> ----
>>>>>> Saad
>>>>>> 
>>>>>> 
>>>>>> On Thu, Dec 1, 2016 at 2:56 PM, John Leach <jleach@splicemachine.com>
>>>>> wrote:
>>>>>> 
>>>>>>> Saad,
>>>>>>> 
>>>>>>> Did you validate that Meta is not on the “Hot” region server?
>>>>>>> 
>>>>>>> Regards,
>>>>>>> John Leach
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>>> On Dec 1, 2016, at 1:50 PM, Saad Mufti <saad.mufti@gmail.com>
>>> wrote:
>>>>>>>> 
>>>>>>>> Hi,
>>>>>>>> 
>>>>>>>> We are using HBase 1.0 on CDH 5.5.2 . We have taken great
care to
>>> avoid
>>>>>>>> hotspotting due to inadvertent data patterns by prepending
an MD5
>>>>> based 4
>>>>>>>> digit hash prefix to all our data keys. This works fine most
of the
>>>>>>> times,
>>>>>>>> but more and more (as much as once or twice a day) recently
we have
>>>>>>>> occasions where one region server suddenly becomes "hot"
(CPU above
>>> or
>>>>>>>> around 95% in various monitoring tools). When it happens
it lasts
>>> for
>>>>>>>> hours, occasionally the hotspot might jump to another region
server
>>> as
>>>>>>> the
>>>>>>>> master decide the region is unresponsive and gives its region
to
>>>>> another
>>>>>>>> server.
>>>>>>>> 
>>>>>>>> For the longest time, we thought this must be some single
rogue key
>>> in
>>>>>>> our
>>>>>>>> input data that is being hammered. All attempts to track
this down
>>> have
>>>>>>>> failed though, and the following behavior argues against
this being
>>>>>>>> application based:
>>>>>>>> 
>>>>>>>> 1. plotted Get and Put rate by region on the "hot" region
server in
>>>>>>>> Cloudera Manager Charts, shows no single region is an outlier.
>>>>>>>> 
>>>>>>>> 2. cleanly restarting just the region server process causes
its
>>> regions
>>>>>>> to
>>>>>>>> randomly migrate to other region servers, then it gets new
ones from
>>>>> the
>>>>>>>> HBase master, basically a sort of shuffling, then the hotspot
goes
>>>>> away.
>>>>>>> If
>>>>>>>> it were application based, you'd expect the hotspot to just
jump to
>>>>>>> another
>>>>>>>> region server.
>>>>>>>> 
>>>>>>>> 3. have pored through region server logs and can't see anything
out
>>> of
>>>>>>> the
>>>>>>>> ordinary happening
>>>>>>>> 
>>>>>>>> The only other pertinent thing to mention might be that we
have a
>>>>> special
>>>>>>>> process of our own running outside the cluster that does
cluster
>>> wide
>>>>>>> major
>>>>>>>> compaction in a rolling fashion, where each batch consists
of one
>>>>> region
>>>>>>>> from each region server, and it waits before one batch is
completely
>>>>> done
>>>>>>>> before starting another. We have seen no real impact on the
hotspot
>>>>> from
>>>>>>>> shutting this down and in normal times it doesn't impact
our read or
>>>>>>> write
>>>>>>>> performance much.
>>>>>>>> 
>>>>>>>> We are at our wit's end, anyone have experience with a scenario
like
>>>>>>> this?
>>>>>>>> Any help/guidance would be most appreciated.
>>>>>>>> 
>>>>>>>> -----
>>>>>>>> Saad
>>>>>>> 
>>>>>>> 
>>>>> 
>>>>> 
>>> 
>> 
>> 


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