Andrew thanks. I think this indeed was the problem.
To get over it, I increased the amount of memory given the region server to
avoid IO on reads. I used the configs below. In my experiments, I have writers
streaming their output to HBase. The reader powers a web page and does this
scatter/gather, where it reads 1000 keys written last and passes them the the
front end. With this workload, I get the exception below at the region server.
Again, I am using HBAse (0.98.6.1). Any help is appreciated.
hbase-env:HBASE_REGIONSERVER_OPTS=-Xmx6G -XX:MaxDirectMemorySize=5G
-XX:CMSInitiatingOccupancyFraction=88 -XX:+AggressiveOpts -verbose:gc
-XX:+PrintGCDetails -XX:+PrintGCTimeStamps -Xlog
gc:/tmp/hbase-regionserver-gc.log
hbase-site:hbase.bucketcache.ioengine=offheap
hfile.block.cache.size=0.4
hbase.bucketcache.size=4196
hbase.rs.cacheblocksonwrite=true
hfile.block.index.cacheonwrite=true
hfile.block.bloom.cacheonwrite=true
2014-10-10 15:06:44,173 ERROR
[B.DefaultRpcServer.handler=62,queue=2,port=60020] ipc.RpcServer: Unexpected
throwable object
java.lang.IllegalArgumentException
at java.nio.Buffer.position(Buffer.java:236)
at
org.apache.hadoop.hbase.util.ByteBufferUtils.skip(ByteBufferUtils.java:434)
at
org.apache.hadoop.hbase.io.hfile.HFileReaderV2$ScannerV2.readKeyValueLen(HFileReaderV2.java:849)
at
org.apache.hadoop.hbase.io.hfile.HFileReaderV2$ScannerV2.next(HFileReaderV2.java:760)
at
org.apache.hadoop.hbase.regionserver.StoreFileScanner.seekAtOrAfter(StoreFileScanner.java:248)
at
org.apache.hadoop.hbase.regionserver.StoreFileScanner.seek(StoreFileScanner.java:152)
at
org.apache.hadoop.hbase.regionserver.StoreScanner.seekScanners(StoreScanner.java:317)
at
org.apache.hadoop.hbase.regionserver.StoreScanner.<init>(StoreScanner.java:176)
at
org.apache.hadoop.hbase.regionserver.HStore.getScanner(HStore.java:1780)
at
org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.<init>(HRegion.java:3758)
at
org.apache.hadoop.hbase.regionserver.HRegion.instantiateRegionScanner(HRegion.java:1950)
at
org.apache.hadoop.hbase.regionserver.HRegion.getScanner(HRegion.java:1936)
at
org.apache.hadoop.hbase.regionserver.HRegion.getScanner(HRegion.java:1913)
at
org.apache.hadoop.hbase.regionserver.HRegionServer.scan(HRegionServer.java:3157)
at
org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ClientService$2.callBlockingMethod(ClientProtos.java:29587)
at org.apache.hadoop.hbase.ipc.RpcServer.call(RpcServer.java:2027)
at org.apache.hadoop.hbase.ipc.CallRunner.run(CallRunner.java:108)
at
org.apache.hadoop.hbase.ipc.RpcExecutor.consumerLoop(RpcExecutor.java:114)
at org.apache.hadoop.hbase.ipc.RpcExecutor$1.run(RpcExecutor.java:94)
at java.lang.Thread.run(Thread.java:744)
> From: apurt...@apache.org
> Date: Tue, 7 Oct 2014 17:09:35 -0700
> Subject: Re: HBase read performance
> To: user@hbase.apache.org
>
> > The cluster has 2 m1.large nodes.
>
> That's the problem right there.
>
> You need to look at c3.4xlarge or i2 instances as a minimum requirement. M1
> and even M3 instance types have ridiculously poor IO.
>
>
> On Tue, Oct 7, 2014 at 3:01 PM, Khaled Elmeleegy <kd...@hotmail.com> wrote:
>
> > Thanks Nicolas, Qiang.
> >
> > I was able to write a simple program that reproduces the problem on a tiny
> > HBase cluster on ec2. The cluster has 2 m1.large nodes. One node runs the
> > master, name node and zookeeper. The other node runs a data node and a
> > region server, with heap size configured to be 6GB. There, the 1000
> > parallel reverse gets (reverse scans) take 7-8 seconds. The data set is
> > tiny (10M records, each having a small number of bytes). As I said before,
> > all hardware resources are very idle there.
> >
> > Interestingly, running the same workload on my macbook, the 1000 parallel
> > gets take ~200ms on a pseudo-distributed installation.
> >
> > Any help to resolve this mystery is highly appreciated.
> >
> > P.S. please find my test program attached.
> >
> > Best,
> > Khaled
> >
> > > From: nkey...@gmail.com
> > > Date: Mon, 6 Oct 2014 09:40:48 +0200
> > > Subject: Re: HBase read performance
> > > To: user@hbase.apache.org
> > >
> > > Hi,
> > >
> > > I haven't seen it mentioned, but if I understand correctly each scan
> > > returns a single row? If so you should use Scan#setSmall to save some rpc
> > > calls.
> > >
> > > Cheers,
> > >
> > > Nicolas
> > >
> > >
> > > On Sun, Oct 5, 2014 at 11:28 AM, Qiang Tian <tian...@gmail.com> wrote:
> > >
> > > > when using separate HConnection instance, both its
> > > > RpcClient instance(maintain connection to a regionserver) and Registry
> > > > instance(maintain connection to zookeeper) will be separate..
> > > >
> > > > see
> > > >
> > > >
> > http://shammijayasinghe.blogspot.com/2012/02/zookeeper-increase-maximum-number-of.html
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > On Sun, Oct 5, 2014 at 2:24 PM, Khaled Elmeleegy <kd...@hotmail.com>
> > > > wrote:
> > > >
> > > > > I tried creating my own HConnections pool to use for my HBase calls,
> > so
> > > > > that not all the (2K) threads share the same HConnection. However, I
> > > > could
> > > > > only have 10 HConnections. Beyond that I get ZK exceptions, please
> > find
> > > > it
> > > > > below. Also, with 10 HConnections, I don't see noticeable
> > improvement in
> > > > > performance so far.
> > > > > 2014-10-05 06:11:26,490 WARN [main] zookeeper.RecoverableZooKeeper
> > > > > (RecoverableZooKeeper.java:retryOrThrow(253)) - Possibly transient
> > > > > ZooKeeper, quorum=54.68.206.252:2181,
> > > > >
> > exception=org.apache.zookeeper.KeeperException$ConnectionLossException:
> > > > > KeeperErrorCode = ConnectionLoss for /hbase/hbaseid2014-10-05
> > > > 06:11:26,490
> > > > > INFO [main] util.RetryCounter
> > > > (RetryCounter.java:sleepUntilNextRetry(155))
> > > > > - Sleeping 1000ms before retry #0...2014-10-05 06:11:27,845 WARN
> > [main]
> > > > > zookeeper.RecoverableZooKeeper
> > > > > (RecoverableZooKeeper.java:retryOrThrow(253)) - Possibly transient
> > > > > ZooKeeper, quorum=54.68.206.252:2181,
> > > > >
> > exception=org.apache.zookeeper.KeeperException$ConnectionLossException:
> > > > > KeeperErrorCode = ConnectionLoss for /hbase/hbaseid2014-10-05
> > > > 06:11:27,849
> > > > > INFO [main] util.RetryCounter
> > > > (RetryCounter.java:sleepUntilNextRetry(155))
> > > > > - Sleeping 2000ms before retry #1...2014-10-05 06:11:30,405 WARN
> > [main]
> > > > > zookeeper.RecoverableZooKeeper
> > > > > (RecoverableZooKeeper.java:retryOrThrow(253)) - Possibly transient
> > > > > ZooKeeper, quorum=54.68.206.252:2181,
> > > > >
> > exception=org.apache.zookeeper.KeeperException$ConnectionLossException:
> > > > > KeeperErrorCode = ConnectionLoss for /hbase/hbaseid2014-10-05
> > > > 06:11:30,405
> > > > > INFO [main] util.RetryCounter
> > > > (RetryCounter.java:sleepUntilNextRetry(155))
> > > > > - Sleeping 4000ms before retry #2...2014-10-05 06:11:35,278 WARN
> > [main]
> > > > > zookeeper.RecoverableZooKeeper
> > > > > (RecoverableZooKeeper.java:retryOrThrow(253)) - Possibly transient
> > > > > ZooKeeper, quorum=54.68.206.252:2181,
> > > > >
> > exception=org.apache.zookeeper.KeeperException$ConnectionLossException:
> > > > > KeeperErrorCode = ConnectionLoss for /hbase/hbaseid2014-10-05
> > > > 06:11:35,279
> > > > > INFO [main] util.RetryCounter
> > > > (RetryCounter.java:sleepUntilNextRetry(155))
> > > > > - Sleeping 8000ms before retry #3...2014-10-05 06:11:44,393 WARN
> > [main]
> > > > > zookeeper.RecoverableZooKeeper
> > > > > (RecoverableZooKeeper.java:retryOrThrow(253)) - Possibly transient
> > > > > ZooKeeper, quorum=54.68.206.252:2181,
> > > > >
> > exception=org.apache.zookeeper.KeeperException$ConnectionLossException:
> > > > > KeeperErrorCode = ConnectionLoss for /hbase/hbaseid2014-10-05
> > > > 06:11:44,393
> > > > > ERROR [main] zookeeper.RecoverableZooKeeper
> > > > > (RecoverableZooKeeper.java:retryOrThrow(255)) - ZooKeeper exists
> > failed
> > > > > after 4 attempts2014-10-05 06:11:44,394 WARN [main] zookeeper.ZKUtil
> > > > > (ZKUtil.java:checkExists(482)) - hconnection-0x4e174f3b, quorum=
> > > > > 54.68.206.252:2181, baseZNode=/hbase Unable to set watcher on znode
> > > > >
> > > >
> > (/hbase/hbaseid)org.apache.zookeeper.KeeperException$ConnectionLossException:
> > > > > KeeperErrorCode = ConnectionLoss for /hbase/hbaseid at
> > > > > org.apache.zookeeper.KeeperException.create(KeeperException.java:99)
> > at
> > > > > org.apache.zookeeper.KeeperException.create(KeeperException.java:51)
> > at
> > > > > org.apache.zookeeper.ZooKeeper.exists(ZooKeeper.java:1041) at
> > > > >
> > > >
> > org.apache.hadoop.hbase.zookeeper.RecoverableZooKeeper.exists(RecoverableZooKeeper.java:199)
> > > > > at
> > org.apache.hadoop.hbase.zookeeper.ZKUtil.checkExists(ZKUtil.java:479)
> > > > > at
> > > > >
> > > >
> > org.apache.hadoop.hbase.zookeeper.ZKClusterId.readClusterIdZNode(ZKClusterId.java:65)
> > > > > at
> > > > >
> > > >
> > org.apache.hadoop.hbase.client.ZooKeeperRegistry.getClusterId(ZooKeeperRegistry.java:83)
> > > > > at
> > > > >
> > > >
> > org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation.retrieveClusterId(HConnectionManager.java:857)
> > > > > at
> > > > >
> > > >
> > org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation.<init>(HConnectionManager.java:662)
> > > > > at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native
> > > > > Method) at
> > > > >
> > > >
> > sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
> > > > > at
> > > > >
> > > >
> > sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
> > > > > at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
> > > > at
> > > > >
> > > >
> > org.apache.hadoop.hbase.client.HConnectionManager.createConnection(HConnectionManager.java:414)
> > > > > at
> > > > >
> > > >
> > org.apache.hadoop.hbase.client.HConnectionManager.createConnection(HConnectionManager.java:335)...
> > > > > > From: kd...@hotmail.com
> > > > > > To: user@hbase.apache.org
> > > > > > Subject: RE: HBase read performance
> > > > > > Date: Fri, 3 Oct 2014 12:37:39 -0700
> > > > > >
> > > > > > Lars, Ted, and Qiang,
> > > > > > Thanks for all the input.
> > > > > > Qiang: yes all the threads are in the same client process sharing
> > the
> > > > > same connection. And since I don't see hardware contention, may be
> > there
> > > > is
> > > > > contention over this code path. I'll try using many connections and
> > see
> > > > if
> > > > > it alleviates the problems and I'll report back.
> > > > > > Thanks again,Khaled
> > > > > >
> > > > > > > Date: Fri, 3 Oct 2014 15:18:30 +0800
> > > > > > > Subject: Re: HBase read performance
> > > > > > > From: tian...@gmail.com
> > > > > > > To: user@hbase.apache.org
> > > > > > >
> > > > > > > Regarding to profiling, Andrew introduced
> > > > > > >
> > http://www.brendangregg.com/blog/2014-06-12/java-flame-graphs.html
> > > > > months
> > > > > > > ago.
> > > > > > >
> > > > > > > processCallTime comes from RpcServer#call, so it looks good?
> > > > > > >
> > > > > > > I have a suspect:
> > https://issues.apache.org/jira/browse/HBASE-11306
> > > > > > >
> > > > > > > how many processes do you have for your 2000 threads?
> > > > > > > if olny 1 process, those threads will share just 1 connection to
> > that
> > > > > > > regionserver, there might be big contention on the RPC code path.
> > > > > ---for
> > > > > > > such case, could you try using different connections?
> > > > > > >
> > > > >
> > > >
> > https://hbase.apache.org/apidocs/org/apache/hadoop/hbase/client/HConnectionManager.html
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > On Fri, Oct 3, 2014 at 9:55 AM, Ted Yu <yuzhih...@gmail.com>
> > wrote:
> > > > > > >
> > > > > > > > Khaled:
> > > > > > > > Do you have profiler such as jprofiler ?
> > > > > > > > Profiling would give us more hint.
> > > > > > > >
> > > > > > > > Otherwise capturing stack trace during the period of reverse
> > scan
> > > > > would
> > > > > > > > help.
> > > > > > > >
> > > > > > > > Cheers
> > > > > > > >
> > > > > > > > On Thu, Oct 2, 2014 at 4:52 PM, lars hofhansl <
> > la...@apache.org>
> > > > > wrote:
> > > > > > > >
> > > > > > > > > You might have the data in the OS buffer cache, without short
> > > > > circuit
> > > > > > > > > reading the region server has to request the block from the
> > data
> > > > > node
> > > > > > > > > process, which then reads it from the block cache.
> > > > > > > > > That is a few context switches per RPC that do not show up
> > in CPU
> > > > > > > > metrics.
> > > > > > > > > In that you also would not see disk IO.
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > If - as you say - you see a lot of evicted blocks the data
> > *has*
> > > > > to come
> > > > > > > > > from the OS. If you do not see disk IO is *has* to come from
> > the
> > > > OS
> > > > > > > > cache.
> > > > > > > > > I.e. there's more RAM on your boxes, and you should increase
> > the
> > > > > heap
> > > > > > > > block
> > > > > > > > > cache.
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > You can measure the context switches with vmstat. Other than
> > that
> > > > > I have
> > > > > > > > > no suggestion until I reproduce the problem.
> > > > > > > > > Also check the data locality index of the region server it
> > should
> > > > > be
> > > > > > > > close
> > > > > > > > > to 100%.
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > -- Lars
> > > > > > > > >
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > ________________________________
> > > > > > > > > From: Khaled Elmeleegy <kd...@hotmail.com>
> > > > > > > > > To: "user@hbase.apache.org" <user@hbase.apache.org>
> > > > > > > > > Sent: Thursday, October 2, 2014 3:24 PM
> > > > > > > > > Subject: RE: HBase read performance
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > Lars thanks a lot about all the tips. I'll make sure I cover
> > all
> > > > > of them
> > > > > > > > > and get back to you. I am not sure they are the bottleneck
> > though
> > > > > as they
> > > > > > > > > all are about optimizing physical resource usage. As I said,
> > I
> > > > > don't see
> > > > > > > > > any contended physical resources now. I'll also try to
> > reproduce
> > > > > this
> > > > > > > > > problem in a simpler environment and pass to you the test
> > program
> > > > > to play
> > > > > > > > > with.
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > Couple of high level points to make. You are right that my
> > use
> > > > > case is
> > > > > > > > > kind of a worst case for HBase reads. But, if things go the
> > way
> > > > you
> > > > > > > > > described them, there should be tons of disk IO and that
> > should
> > > > be
> > > > > > > > clearly
> > > > > > > > > the bottleneck. This is not the case though. That's for the
> > > > simple
> > > > > reason
> > > > > > > > > that this is done in a test environment (I am still
> > prototyping),
> > > > > and
> > > > > > > > not a
> > > > > > > > > lot of data is yet written to HBase. However for the real use
> > > > > case, there
> > > > > > > > > should writers constantly writing data to HBase and readers
> > > > > occasionally
> > > > > > > > > doing this scatter/gather. At steady state, things should
> > only
> > > > get
> > > > > worse
> > > > > > > > > and all the issues you mentioned should get far more
> > pronounced.
> > > > > At this
> > > > > > > > > point, one can try to mitigate it using more memory or so. I
> > am
> > > > > not there
> > > > > > > > > yet as I think I am hitting some software bottleneck, which I
> > > > > don't know
> > > > > > > > > how to work around.
> > > > > > > > >
> > > > > > > > > Khaled
> > > > > > > > >
> > > > > > > > >
> > > > > > > > >
> > > > > > > > >
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > ----------------------------------------
> > > > > > > > > > Date: Thu, 2 Oct 2014 14:20:47 -0700
> > > > > > > > > > From: la...@apache.org
> > > > > > > > > > Subject: Re: HBase read performance
> > > > > > > > > > To: user@hbase.apache.org
> > > > > > > > > >
> > > > > > > > > > OK... We might need to investigate this.
> > > > > > > > > > Any chance that you can provide a minimal test program and
> > > > > instruction
> > > > > > > > > about how to set it up.
> > > > > > > > > > We can do some profiling then.
> > > > > > > > > >
> > > > > > > > > > One thing to note is that with scanning HBase cannot use
> > bloom
> > > > > filters
> > > > > > > > > to rule out HFiles ahead of time, it needs to look into all
> > of
> > > > > them.
> > > > > > > > > > So you kind of hit on the absolute worst case:
> > > > > > > > > > - random reads that do not fit into the block cache
> > > > > > > > > > - cannot use bloom filters
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > Few more question/comments:
> > > > > > > > > > - Do you have short circuit reading enabled? If not, you
> > > > should.
> > > > > > > > > > - Is your table major compacted? That will reduce the
> > number of
> > > > > files
> > > > > > > > to
> > > > > > > > > look at.
> > > > > > > > > > - Did you disable Nagle's everywhere (enabled tcpnodelay)?
> > It
> > > > > disabled
> > > > > > > > > by default in HBase, but necessarily in your install of HDFS.
> > > > > > > > > > - Which version of HDFS are you using as backing
> > filesystem?
> > > > > > > > > > - If your disk is idle, it means the data fits into the OS
> > > > buffer
> > > > > > > > cache.
> > > > > > > > > In turn that means that you increase the heap for the region
> > > > > servers. You
> > > > > > > > > can also use block encoding (FAST_DIFF) to try to make sure
> > the
> > > > > entire
> > > > > > > > > working set fits into the cache.
> > > > > > > > > >
> > > > > > > > > > - Also try to reduce the block size - although if your
> > overall
> > > > > working
> > > > > > > > > set does not fit in the heap it won't help much.
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > This is a good section of the book to read through
> > generally
> > > > > (even
> > > > > > > > > though you might know most of this already):
> > > > > > > > > http://hbase.apache.org/book.html#perf.configurations
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > -- Lars
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > ----- Original Message -----
> > > > > > > > > > From: Khaled Elmeleegy <kd...@hotmail.com>
> > > > > > > > > > To: "user@hbase.apache.org" <user@hbase.apache.org>
> > > > > > > > > > Cc:
> > > > > > > > > > Sent: Thursday, October 2, 2014 11:27 AM
> > > > > > > > > > Subject: RE: HBase read performance
> > > > > > > > > >
> > > > > > > > > > I do see a very brief spike in CPU (user/system), but it's
> > no
> > > > > where
> > > > > > > > near
> > > > > > > > > 0% idle. It goes from 99% idle down to something like 40%
> > idle
> > > > for
> > > > > a
> > > > > > > > second
> > > > > > > > > or so. The thing to note, this is all on a test cluster, so
> > no
> > > > > real load.
> > > > > > > > > Things are generally idle until i issue 2-3 of these
> > > > > multi-scan-requests
> > > > > > > > to
> > > > > > > > > render a web page. Then, you see the spike in the cpu and
> > some
> > > > > activity
> > > > > > > > in
> > > > > > > > > the network and disk, but nowhere near saturation.
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > If there are specific tests you'd like me to do to debug
> > this,
> > > > > I'd be
> > > > > > > > > more than happy to do it.
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > Khaled
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > ----------------------------------------
> > > > > > > > > >> Date: Thu, 2 Oct 2014 11:15:59 -0700
> > > > > > > > > >> From: la...@apache.org
> > > > > > > > > >> Subject: Re: HBase read performance
> > > > > > > > > >> To: user@hbase.apache.org
> > > > > > > > > >>
> > > > > > > > > >> I still think you're waiting on disk. No IOWAIT? So CPU
> > is not
> > > > > waiting
> > > > > > > > > a lot for IO. No high User/System CPU either?
> > > > > > > > > >>
> > > > > > > > > >> If you see a lot of evicted block then each RPC has a high
> > > > > chance of
> > > > > > > > > requiring to bring an entire 64k block in. You'll see bad
> > > > > performance
> > > > > > > > with
> > > > > > > > > this.
> > > > > > > > > >>
> > > > > > > > > >> We might need to trace this specific scenario.
> > > > > > > > > >>
> > > > > > > > > >> -- Lars
> > > > > > > > > >>
> > > > > > > > > >>
> > > > > > > > > >>
> > > > > > > > > >> ________________________________
> > > > > > > > > >> From: Khaled Elmeleegy <kd...@hotmail.com>
> > > > > > > > > >> To: "user@hbase.apache.org" <user@hbase.apache.org>
> > > > > > > > > >> Sent: Thursday, October 2, 2014 10:46 AM
> > > > > > > > > >> Subject: RE: HBase read performance
> > > > > > > > > >>
> > > > > > > > > >>
> > > > > > > > > >> I've set the heap size to 6GB and I do have gc logging. No
> > > > long
> > > > > pauses
> > > > > > > > > there -- occasional 0.1s or 0.2s.
> > > > > > > > > >>
> > > > > > > > > >> Other than the discrepancy between what's reported on the
> > > > > client and
> > > > > > > > > what's reported at the RS, there is also the issue of not
> > getting
> > > > > proper
> > > > > > > > > concurrency. So, even if a reverse get takes 100ms or so
> > (this
> > > > has
> > > > > to be
> > > > > > > > > mostly blocking on various things as no physical resource is
> > > > > contended),
> > > > > > > > > then the other gets/scans should be able to proceed in
> > parallel,
> > > > > so a
> > > > > > > > > thousand concurrent gets/scans should finish in few hundreds
> > of
> > > > ms
> > > > > not
> > > > > > > > many
> > > > > > > > > seconds. That's why I thought I'd increase the handlers
> > count to
> > > > > try to
> > > > > > > > get
> > > > > > > > > more concurrency, but it didn't help. So, there must be
> > something
> > > > > else.
> > > > > > > > > >>
> > > > > > > > > >> Khaled
> > > > > > > > > >>
> > > > > > > > > >> ----------------------------------------
> > > > > > > > > >>> From: ndimi...@gmail.com
> > > > > > > > > >>> Date: Thu, 2 Oct 2014 10:36:39 -0700
> > > > > > > > > >>> Subject: Re: HBase read performance
> > > > > > > > > >>> To: user@hbase.apache.org
> > > > > > > > > >>>
> > > > > > > > > >>> Do check again on the heap size of the region servers.
> > The
> > > > > default
> > > > > > > > > >>> unconfigured size is 1G; too small for much of anything.
> > > > Check
> > > > > your
> > > > > > > > RS
> > > > > > > > > logs
> > > > > > > > > >>> -- look for lines produced by the JVMPauseMonitor thread.
> > > > They
> > > > > > > > usually
> > > > > > > > > >>> correlate with long GC pauses or other process-freeze
> > events.
> > > > > > > > > >>>
> > > > > > > > > >>> Get is implemented as a Scan of a single row, so a
> > reverse
> > > > > scan of a
> > > > > > > > > single
> > > > > > > > > >>> row should be functionally equivalent.
> > > > > > > > > >>>
> > > > > > > > > >>> In practice, I have seen discrepancy between the
> > latencies
> > > > > reported
> > > > > > > > by
> > > > > > > > > the
> > > > > > > > > >>> RS and the latencies experienced by the client. I've not
> > > > > investigated
> > > > > > > > > this
> > > > > > > > > >>> area thoroughly.
> > > > > > > > > >>>
> > > > > > > > > >>> On Thu, Oct 2, 2014 at 10:05 AM, Khaled Elmeleegy <
> > > > > kd...@hotmail.com
> > > > > > > > >
> > > > > > > > > wrote:
> > > > > > > > > >>>
> > > > > > > > > >>>> Thanks Lars for your quick reply.
> > > > > > > > > >>>>
> > > > > > > > > >>>> Yes performance is similar with less handlers (I tried
> > with
> > > > > 100
> > > > > > > > > first).
> > > > > > > > > >>>>
> > > > > > > > > >>>> The payload is not big ~1KB or so. The working set
> > doesn't
> > > > > seem to
> > > > > > > > > fit in
> > > > > > > > > >>>> memory as there are many cache misses. However, disk is
> > far
> > > > > from
> > > > > > > > > being a
> > > > > > > > > >>>> bottleneck. I checked using iostat. I also verified that
> > > > > neither the
> > > > > > > > > >>>> network nor the CPU of the region server or the client
> > are a
> > > > > > > > > bottleneck.
> > > > > > > > > >>>> This leads me to believe that likely this is a software
> > > > > bottleneck,
> > > > > > > > > >>>> possibly due to a misconfiguration on my side. I just
> > don't
> > > > > know how
> > > > > > > > > to
> > > > > > > > > >>>> debug it. A clear disconnect I see is the individual
> > request
> > > > > latency
> > > > > > > > > as
> > > > > > > > > >>>> reported by metrics on the region server (IPC
> > > > processCallTime
> > > > > vs
> > > > > > > > > scanNext)
> > > > > > > > > >>>> vs what's measured on the client. Does this sound
> > right? Any
> > > > > ideas
> > > > > > > > on
> > > > > > > > > how
> > > > > > > > > >>>> to better debug it?
> > > > > > > > > >>>>
> > > > > > > > > >>>> About this trick with the timestamps to be able to do a
> > > > > forward
> > > > > > > > scan,
> > > > > > > > > >>>> thanks for pointing it out. Actually, I am aware of it.
> > The
> > > > > problem
> > > > > > > > I
> > > > > > > > > have
> > > > > > > > > >>>> is, sometimes I want to get the key after a particular
> > > > > timestamp and
> > > > > > > > > >>>> sometimes I want to get the key before, so just relying
> > on
> > > > > the key
> > > > > > > > > order
> > > > > > > > > >>>> doesn't work. Ideally, I want a reverse get(). I thought
> > > > > reverse
> > > > > > > > scan
> > > > > > > > > can
> > > > > > > > > >>>> do the trick though.
> > > > > > > > > >>>>
> > > > > > > > > >>>> Khaled
> > > > > > > > > >>>>
> > > > > > > > > >>>> ----------------------------------------
> > > > > > > > > >>>>> Date: Thu, 2 Oct 2014 09:40:37 -0700
> > > > > > > > > >>>>> From: la...@apache.org
> > > > > > > > > >>>>> Subject: Re: HBase read performance
> > > > > > > > > >>>>> To: user@hbase.apache.org
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> Hi Khaled,
> > > > > > > > > >>>>> is it the same with fewer threads? 1500 handler threads
> > > > > seems to
> > > > > > > > be a
> > > > > > > > > >>>> lot. Typically a good number of threads depends on the
> > > > > hardware
> > > > > > > > > (number of
> > > > > > > > > >>>> cores, number of spindles, etc). I cannot think of any
> > type
> > > > of
> > > > > > > > > scenario
> > > > > > > > > >>>> where more than 100 would give any improvement.
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> How large is the payload per KV retrieved that way? If
> > > > large
> > > > > (as
> > > > > > > > in a
> > > > > > > > > >>>> few 100k) you definitely want to lower the number of the
> > > > > handler
> > > > > > > > > threads.
> > > > > > > > > >>>>> How much heap do you give the region server? Does the
> > > > > working set
> > > > > > > > fit
> > > > > > > > > >>>> into the cache? (i.e. in the metrics, do you see the
> > > > eviction
> > > > > count
> > > > > > > > > going
> > > > > > > > > >>>> up, if so it does not fit into the cache).
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> If the working set does not fit into the cache
> > (eviction
> > > > > count goes
> > > > > > > > > up)
> > > > > > > > > >>>> then HBase will need to bring a new block in from disk
> > on
> > > > > each Get
> > > > > > > > > >>>> (assuming the Gets are more or less random as far as the
> > > > > server is
> > > > > > > > > >>>> concerned).
> > > > > > > > > >>>>> In case you'll benefit from reducing the HFile block
> > size
> > > > > (from 64k
> > > > > > > > > to
> > > > > > > > > >>>> 8k or even 4k).
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> Lastly I don't think we tested the performance of using
> > > > > reverse
> > > > > > > > scan
> > > > > > > > > >>>> this way, there is probably room to optimize this.
> > > > > > > > > >>>>> Can you restructure your keys to allow forwards
> > scanning?
> > > > For
> > > > > > > > example
> > > > > > > > > >>>> you could store the time as MAX_LONG-time. Or you could
> > > > > invert all
> > > > > > > > > the bits
> > > > > > > > > >>>> of the time portion of the key, so that it sort the
> > other
> > > > > way. Then
> > > > > > > > > you
> > > > > > > > > >>>> could do a forward scan.
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> Let us know how it goes.
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> -- Lars
> > > > > > > > > >>>>>
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> ----- Original Message -----
> > > > > > > > > >>>>> From: Khaled Elmeleegy <kd...@hotmail.com>
> > > > > > > > > >>>>> To: "user@hbase.apache.org" <user@hbase.apache.org>
> > > > > > > > > >>>>> Cc:
> > > > > > > > > >>>>> Sent: Thursday, October 2, 2014 12:12 AM
> > > > > > > > > >>>>> Subject: HBase read performance
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> Hi,
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> I am trying to do a scatter/gather on hbase (0.98.6.1),
> > > > > where I
> > > > > > > > have
> > > > > > > > > a
> > > > > > > > > >>>> client reading ~1000 keys from an HBase table. These
> > keys
> > > > > happen to
> > > > > > > > > fall on
> > > > > > > > > >>>> the same region server. For my reads I use reverse scan
> > to
> > > > > read each
> > > > > > > > > key as
> > > > > > > > > >>>> I want the key prior to a specific time stamp (time
> > stamps
> > > > are
> > > > > > > > stored
> > > > > > > > > in
> > > > > > > > > >>>> reverse order). I don't believe gets can accomplish
> > that,
> > > > > right? so
> > > > > > > > I
> > > > > > > > > use
> > > > > > > > > >>>> scan, with caching set to 1.
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> I use 2000 reader threads in the client and on HBase,
> > I've
> > > > > set
> > > > > > > > > >>>> hbase.regionserver.handler.count to 1500. With this
> > setup,
> > > > my
> > > > > > > > scatter
> > > > > > > > > >>>> gather is very slow and can take up to 10s in total.
> > Timing
> > > > an
> > > > > > > > > individual
> > > > > > > > > >>>> getScanner(..) call on the client side, it can easily
> > take
> > > > few
> > > > > > > > > hundreds of
> > > > > > > > > >>>> ms. I also got the following metrics from the region
> > server
> > > > in
> > > > > > > > > question:
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> "queueCallTime_mean" : 2.190855525775637,
> > > > > > > > > >>>>> "queueCallTime_median" : 0.0,
> > > > > > > > > >>>>> "queueCallTime_75th_percentile" : 0.0,
> > > > > > > > > >>>>> "queueCallTime_95th_percentile" : 1.0,
> > > > > > > > > >>>>> "queueCallTime_99th_percentile" : 556.9799999999818,
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> "processCallTime_min" : 0,
> > > > > > > > > >>>>> "processCallTime_max" : 12755,
> > > > > > > > > >>>>> "processCallTime_mean" : 105.64873440912682,
> > > > > > > > > >>>>> "processCallTime_median" : 0.0,
> > > > > > > > > >>>>> "processCallTime_75th_percentile" : 2.0,
> > > > > > > > > >>>>> "processCallTime_95th_percentile" : 7917.95,
> > > > > > > > > >>>>> "processCallTime_99th_percentile" : 8876.89,
> > > > > > > > > >>>>>
> > > > > > > > > >>>>>
> > > > > > > > > >>>>
> > > > > > > > >
> > > > > > > >
> > > > >
> > > >
> > "namespace_default_table_delta_region_87be70d7710f95c05cfcc90181d183b4_metric_scanNext_min"
> > > > > > > > > >>>> : 89,
> > > > > > > > > >>>>>
> > > > > > > > > >>>>
> > > > > > > > >
> > > > > > > >
> > > > >
> > > >
> > "namespace_default_table_delta_region_87be70d7710f95c05cfcc90181d183b4_metric_scanNext_max"
> > > > > > > > > >>>> : 11300,
> > > > > > > > > >>>>>
> > > > > > > > > >>>>
> > > > > > > > >
> > > > > > > >
> > > > >
> > > >
> > "namespace_default_table_delta_region_87be70d7710f95c05cfcc90181d183b4_metric_scanNext_mean"
> > > > > > > > > >>>> : 654.4949739797315,
> > > > > > > > > >>>>>
> > > > > > > > > >>>>
> > > > > > > > >
> > > > > > > >
> > > > >
> > > >
> > "namespace_default_table_delta_region_87be70d7710f95c05cfcc90181d183b4_metric_scanNext_median"
> > > > > > > > > >>>> : 101.0,
> > > > > > > > > >>>>>
> > > > > > > > > >>>>
> > > > > > > > >
> > > > > > > >
> > > > >
> > > >
> > "namespace_default_table_delta_region_87be70d7710f95c05cfcc90181d183b4_metric_scanNext_75th_percentile"
> > > > > > > > > >>>> : 101.0,
> > > > > > > > > >>>>>
> > > > > > > > > >>>>
> > > > > > > > >
> > > > > > > >
> > > > >
> > > >
> > "namespace_default_table_delta_region_87be70d7710f95c05cfcc90181d183b4_metric_scanNext_95th_percentile"
> > > > > > > > > >>>> : 101.0,
> > > > > > > > > >>>>>
> > > > > > > > > >>>>
> > > > > > > > >
> > > > > > > >
> > > > >
> > > >
> > "namespace_default_table_delta_region_87be70d7710f95c05cfcc90181d183b4_metric_scanNext_99th_percentile"
> > > > > > > > > >>>> : 113.0,
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> Where "delta" is the name of the table I am querying.
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> In addition to all this, i monitored the hardware
> > resources
> > > > > (CPU,
> > > > > > > > > disk,
> > > > > > > > > >>>> and network) of both the client and the region server
> > and
> > > > > nothing
> > > > > > > > > seems
> > > > > > > > > >>>> anywhere near saturation. So I am puzzled by what's
> > going on
> > > > > and
> > > > > > > > > where this
> > > > > > > > > >>>> time is going.
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> Few things to note based on the above measurements:
> > both
> > > > > medians of
> > > > > > > > > IPC
> > > > > > > > > >>>> processCallTime and queueCallTime are basically zero
> > (ms I
> > > > > presume,
> > > > > > > > > >>>> right?). However, scanNext_median is 101 (ms too,
> > right?). I
> > > > > am not
> > > > > > > > > sure
> > > > > > > > > >>>> how this adds up. Also, even though the 101 figure seems
> > > > > > > > outrageously
> > > > > > > > > high
> > > > > > > > > >>>> and I don't know why, still all these scans should be
> > > > > happening in
> > > > > > > > > >>>> parallel, so the overall call should finish fast, given
> > that
> > > > > no
> > > > > > > > > hardware
> > > > > > > > > >>>> resource is contended, right? but this is not what's
> > > > > happening, so I
> > > > > > > > > have
> > > > > > > > > >>>> to be missing something(s).
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> So, any help is appreciated there.
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> Thanks,
> > > > > > > > > >>>>> Khaled
> > > > > > > > > >>>>
> > > > > > > > > >>>>
> > > > > > > > >
> > > > > > > >
> > > > > >
> > > > >
> > > > >
> > > >
> >
>
>
>
> --
> Best regards,
>
> - Andy
>
> Problems worthy of attack prove their worth by hitting back. - Piet Hein
> (via Tom White)
