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From Jeff Whiting <je...@qualtrics.com>
Subject Re: Struggling with Region Servers Running out of Memory
Date Thu, 01 Nov 2012 23:44:14 GMT
So this is some of what I'm seeing as I go through the profiles:

(a) 2GB - org.apache.hadoop.hbase.io.hfile.LruBlockCache
     This looks like it is the block cache and we aren't having any problems with that...

(b) 1.4GB - org.apache.hadoop.hbase.regionserver.HRegionServer -- 
java.util.concurrent.ConcurrentHashMap$Segment[]
     It looks like it belongs to the member variable "onlineRegions" which has a member variable

"segments".
     I'm guessing this is the memstores that hbase is currently holding onto.

(c) 4.3GB -- java.util.concurrent.LinkedBlockingQueue -- 
org.apache.hadoop.hbase.ipc.WritableRpcEngine$Server
    This is the one that keeps growing and not shrinking that is causing us to run out of
memory.  
However the cause isn't immediately clear like the other 2 in MAT.
   These seem to be the references to the LinkedBlockingQueue (you'll need a wide monitor
to read it 
well):
Class Name | Shallow Heap | Retained Heap
---------------------------------------------------------------------------------------------------------------------------------------------------------
java.util.concurrent.LinkedBlockingQueue @ 0x2aaab3583d30 |           80 | 4,616,431,568
|- myCallQueue org.apache.hadoop.hbase.ipc.HBaseServer$Handler @ 0x2aaab50d3c70 REPL IPC Server

handler 2 on 60020 Thread|          192 | 384,392
|- myCallQueue org.apache.hadoop.hbase.ipc.HBaseServer$Handler @ 0x2aaab50d3d30 REPL IPC Server

handler 1 on 60020 Thread|          192 | 384,392
|- myCallQueue org.apache.hadoop.hbase.ipc.HBaseServer$Handler @ 0x2aaab50d3df0 REPL IPC Server

handler 0 on 60020 Thread|          192 | 205,976
|- replicationQueue org.apache.hadoop.hbase.ipc.WritableRpcEngine$Server @ 
0x2aaab392dbe0                                 |          240 |         3,968
---------------------------------------------------------------------------------------------------------------------------------------------------------

So it looks like it is shared between the myCallQueue and the replicationQueue.  JProfiler
is 
showing the same thing.  I'm having a hard time figuring out much more.

(d) 977MB -- In other (no common root)
     This just seems to be other stuff going on in the region server but I'm not really concerned

about it...as I don't think it is the culprit.


Overall it looks like it has to do with replication.  So this cluster is in the middle of
an 
replication chain A -> B -> C where this cluster is B.  So can we tell if it is running
out of 
memory because it is being replicated too?  Or because it is trying to replicate somewhere
else.

Thanks,
~Jeff

On 10/30/2012 11:39 PM, Stack wrote:
> On Mon, Oct 29, 2012 at 3:55 PM, Jeff Whiting <jeffw@qualtrics.com> wrote:
>> However what we are seeing is that our memory usage goes up slowly until the
>> region server starts sputtering due to gc collection issues and it will
>> eventually get timed out by zookeeper and be killed.
>>
> Hey Jeff.  You have GC logging enabled?  Might not tell you more than
> you already know, that something is retaining more and more objects
> over time.   You have a dumped heap?  What have you used to poke at
> it?  You generally want to find the objects that have the deepest size
> (Not all profilers let you do this though).  This is usually enough to
> give you a clue.
>
> Anything particular about the character of your load?  Ram asks if any
> big cells in the mix?
>
> St.Ack
>
>
>
>> At this point I feel somewhat lost as to how to debug the problem. I'm not
>> sure what to do next to figure out what is going on.  Any suggestions as to
>> what to look for or debug where the memory is being used? I can generate
>> heap dumps via jmap (although it effectively kills the region server) but I
>> don't really know what to look for to see where the memory is going. I also
>> have jmx setup on each region server and can connect to it that way.
>>
>> Thanks,
>> ~Jeff
>>
>> --
>> Jeff Whiting
>> Qualtrics Senior Software Engineer
>> jeffw@qualtrics.com
>>

-- 
Jeff Whiting
Qualtrics Senior Software Engineer
jeffw@qualtrics.com


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