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From lars hofhansl <la...@apache.org>
Subject Re: HBase Random Read latency > 100ms
Date Mon, 07 Oct 2013 21:04:25 GMT
He still should not see 100ms latency. 20ms, sure. 100ms seems large; there are still 8 machines
serving the requests.

I agree this spec is far from optimal, but there is still something odd here.


Ramu, this does not look like a GC issue. You'd see much larger (worst case) latencies if
that were the case (dozens of seconds).
Are you using 40 client from 40 different machines? Or from 40 different processes on the
same machine? Or 40 threads in the same process?

Thanks.

-- Lars



________________________________
 From: Vladimir Rodionov <vrodionov@carrieriq.com>
To: "user@hbase.apache.org" <user@hbase.apache.org> 
Sent: Monday, October 7, 2013 11:02 AM
Subject: RE: HBase Random Read latency > 100ms
 

Ramu, your HBase configuration (128GB of heap) is far from optimal.
Nobody runs HBase with that amount of heap to my best knowledge.
32GB of RAM is the usual upper limit. We run 8-12GB in production.

What else, your IO capacity is VERY low. 2 SATA drives in RAID 1 for mostly random reads load?
You should have 8, better 12-16 drives per server. Forget about RAID. You have HDFS.

Block cache in your case does not help much , as since your read amplification is at least
x20 (16KB block and 724 B read) - its just waste
RAM (heap). In your case you do not need LARGE heap and LARGE block cache.

I advise you reconsidering your hardware spec, applying all optimizations mentioned already
in this thread and lowering your expectations.

With a right hardware you will be able to get 500-1000 truly random reads per server.

Best regards,
Vladimir Rodionov
Principal Platform Engineer
Carrier IQ, www.carrieriq.com
e-mail: vrodionov@carrieriq.com

________________________________________

From: Ramu M S [ramu.malur@gmail.com]
Sent: Monday, October 07, 2013 5:23 AM
To: user@hbase.apache.org
Subject: Re: HBase Random Read latency > 100ms

Hi Bharath,

I am little confused about the metrics displayed by Cloudera. Even when
there are no oeprations, the gc_time metric is showing 2s constant in the
graph. Is this the CMS gc_time (in that case no JVm pause) or the GC pause.

GC timings reported earlier is the average taken for gc_time metric for all
region servers.

Regards,
Ramu


On Mon, Oct 7, 2013 at 9:10 PM, Ramu M S <ramu.malur@gmail.com> wrote:

> Jean,
>
> Yes. It is 2 drives.
>
> - Ramu
>
>
> On Mon, Oct 7, 2013 at 8:45 PM, Jean-Marc Spaggiari <
> jean-marc@spaggiari.org> wrote:
>
>> Quick questionon the disk side.
>>
>> When you say:
>> 800 GB SATA (7200 RPM) Disk
>> Is it 1x800GB? It's raid 1, so might be 2 drives? What's the
>> configuration?
>>
>> JM
>>
>>
>> 2013/10/7 Ramu M S <ramu.malur@gmail.com>
>>
>> > Lars, Bharath,
>> >
>> > Compression is disabled for the table. This was not intended from the
>> > evaluation.
>> > I forgot to mention that during table creation. I will enable snappy
>> and do
>> > major compaction again.
>> >
>> > Please suggest other options to try out and also suggestions for the
>> > previous questions.
>> >
>> > Thanks,
>> > Ramu
>> >
>> >
>> > On Mon, Oct 7, 2013 at 6:35 PM, Ramu M S <ramu.malur@gmail.com> wrote:
>> >
>> > > Bharath,
>> > >
>> > > I was about to report this. Yes indeed there is too much of GC time.
>> > > Just verified the GC time using Cloudera Manager statistics(Every
>> minute
>> > > update).
>> > >
>> > > For each Region Server,
>> > >  - During Read: Graph shows 2s constant.
>> > >  - During Compaction: Graph starts with 7s and goes as high as 20s
>> during
>> > > end.
>> > >
>> > > Few more questions,
>> > > 1. For the current evaluation, since the reads are completely random
>> and
>> > I
>> > > don't expect to read same data again can I set the Heap to the
>> default 1
>> > GB
>> > > ?
>> > >
>> > > 2. Can I completely turn off BLOCK CACHE for this table?
>> > >    http://hbase.apache.org/book/regionserver.arch.html recommends
>> that
>> > > for Randm reads.
>> > >
>> > > 3. But in the next phase of evaluation, We are interested to use
>> HBase as
>> > > In-memory KV DB by having the latest data in RAM (To the tune of
>> around
>> > 128
>> > > GB in each RS, we are setting up 50-100 Node Cluster). I am very
>> curious
>> > to
>> > > hear any suggestions in this regard.
>> > >
>> > > Regards,
>> > > Ramu
>> > >
>> > >
>> > > On Mon, Oct 7, 2013 at 5:50 PM, Bharath Vissapragada <
>> > > bharathv@cloudera.com> wrote:
>> > >
>> > >> Hi Ramu,
>> > >>
>> > >> Thanks for reporting the results back. Just curious if you are
>> hitting
>> > any
>> > >> big GC pauses due to block cache churn on such large heap. Do you see
>> > it ?
>> > >>
>> > >> - Bharath
>> > >>
>> > >>
>> > >> On Mon, Oct 7, 2013 at 1:42 PM, Ramu M S <ramu.malur@gmail.com>
>> wrote:
>> > >>
>> > >> > Lars,
>> > >> >
>> > >> > After changing the BLOCKSIZE to 16KB, the latency has reduced
a
>> > little.
>> > >> Now
>> > >> > the average is around 75ms.
>> > >> > Overall throughput (I am using 40 Clients to fetch records) is
>> around
>> > 1K
>> > >> > OPS.
>> > >> >
>> > >> > After compaction hdfsBlocksLocalityIndex is
>> 91,88,78,90,99,82,94,97 in
>> > >> my 8
>> > >> > RS respectively.
>> > >> >
>> > >> > Thanks,
>> > >> > Ramu
>> > >> >
>> > >> >
>> > >> > On Mon, Oct 7, 2013 at 3:51 PM, Ramu M S <ramu.malur@gmail.com>
>> > wrote:
>> > >> >
>> > >> > > Thanks Lars.
>> > >> > >
>> > >> > > I have changed the BLOCKSIZE to 16KB and triggered a major
>> > >> compaction. I
>> > >> > > will report my results once it is done.
>> > >> > >
>> > >> > > - Ramu
>> > >> > >
>> > >> > >
>> > >> > > On Mon, Oct 7, 2013 at 3:21 PM, lars hofhansl <larsh@apache.org>
>> > >> wrote:
>> > >> > >
>> > >> > >> First of: 128gb heap per RegionServer. Wow.I'd be interested
to
>> > hear
>> > >> > your
>> > >> > >> experience with such a large heap for your RS. It's definitely
>> big
>> > >> > enough.
>> > >> > >>
>> > >> > >>
>> > >> > >> It's interesting hat 100gb do fit into the aggregate
cache (of
>> > >> 8x32gb),
>> > >> > >> while 1.8tb do not.
>> > >> > >> Looks like ~70% of the read request would need to bring
in a
>> 64kb
>> > >> block
>> > >> > >> in order to read 724 bytes.
>> > >> > >>
>> > >> > >> Should that take 100ms? No. Something's still amiss.
>> > >> > >>
>> > >> > >> Smaller blocks might help (you'd need to bring in 4,
8, or maybe
>> > 16k
>> > >> to
>> > >> > >> read the small row). You would need to issue a major
compaction
>> for
>> > >> > that to
>> > >> > >> take effect.
>> > >> > >> Maybe try 16k blocks. If that speeds up your random gets
we know
>> > >> where
>> > >> > to
>> > >> > >> look next... At the disk IO.
>> > >> > >>
>> > >> > >>
>> > >> > >> -- Lars
>> > >> > >>
>> > >> > >>
>> > >> > >>
>> > >> > >> ________________________________
>> > >> > >>  From: Ramu M S <ramu.malur@gmail.com>
>> > >> > >> To: user@hbase.apache.org; lars hofhansl <larsh@apache.org>
>> > >> > >> Sent: Sunday, October 6, 2013 11:05 PM
>> > >> > >> Subject: Re: HBase Random Read latency > 100ms
>> > >> > >>
>> > >> > >>
>> > >> > >> Lars,
>> > >> > >>
>> > >> > >> In one of your old posts, you had mentioned that lowering
the
>> > >> BLOCKSIZE
>> > >> > is
>> > >> > >> good for random reads (of course with increased size
for Block
>> > >> Indexes).
>> > >> > >>
>> > >> > >> Post is at
>> > >> > http://grokbase.com/t/hbase/user/11bat80x7m/row-get-very-slow
>> > >> > >>
>> > >> > >> Will that help in my tests? Should I give it a try? If
I alter
>> my
>> > >> table,
>> > >> > >> should I trigger a major compaction again for this to
take
>> effect?
>> > >> > >>
>> > >> > >> Thanks,
>> > >> > >> Ramu
>> > >> > >>
>> > >> > >>
>> > >> > >>
>> > >> > >> On Mon, Oct 7, 2013 at 2:44 PM, Ramu M S <ramu.malur@gmail.com>
>> > >> wrote:
>> > >> > >>
>> > >> > >> > Sorry BLOCKSIZE was wrong in my earlier post, it
is the
>> default
>> > 64
>> > >> KB.
>> > >> > >> >
>> > >> > >> > {NAME => 'usertable', FAMILIES => [{NAME =>
'cf',
>> > >> DATA_BLOCK_ENCODING
>> > >> > =>
>> > >> > >> > 'NONE', BLOOMFILTER => 'ROWCOL', REPLICATION_SCOPE
=> '0',
>> > >> VERSIONS =>
>> > >> > >> '1',
>> > >> > >> > COMPRESSION => 'NONE', MIN_VERSIONS => '0',
TTL =>
>> '2147483647',
>> > >> > >> > KEEP_DELETED_CELLS => 'false', BLOCKSIZE =>
'65536',
>> IN_MEMORY =>
>> > >> > >> 'false',
>> > >> > >> > ENCODE_ON_DISK => 'true', BLOCKCACHE => 'true'}]}
>> > >> > >> >
>> > >> > >> > Thanks,
>> > >> > >> > Ramu
>> > >> > >> >
>> > >> > >> >
>> > >> > >> > On Mon, Oct 7, 2013 at 2:42 PM, Ramu M S <
>> ramu.malur@gmail.com>
>> > >> > wrote:
>> > >> > >> >
>> > >> > >> >> Lars,
>> > >> > >> >>
>> > >> > >> >> - Yes Short Circuit reading is enabled on both
HDFS and
>> HBase.
>> > >> > >> >> - I had issued Major compaction after table
is loaded.
>> > >> > >> >> - Region Servers have max heap set as 128 GB.
Block Cache
>> Size
>> > is
>> > >> > 0.25
>> > >> > >> of
>> > >> > >> >> heap (So 32 GB for each Region Server) Do we
need even more?
>> > >> > >> >> - Decreasing HFile Size (Default is 1GB )? Should
I leave it
>> to
>> > >> > >> default?
>> > >> > >> >> - Keys are Zipfian distributed (By YCSB)
>> > >> > >> >>
>> > >> > >> >> Bharath,
>> > >> > >> >>
>> > >> > >> >> Bloom Filters are enabled. Here is my table
details,
>> > >> > >> >> {NAME => 'usertable', FAMILIES => [{NAME
=> 'cf',
>> > >> DATA_BLOCK_ENCODING
>> > >> > >> =>
>> > >> > >> >> 'NONE', BLOOMFILTER => 'ROWCOL', REPLICATION_SCOPE
=> '0',
>> > >> VERSIONS
>> > >> > =>
>> > >> > >> '1',
>> > >> > >> >> COMPRESSION => 'NONE', MIN_VERSIONS =>
'0', TTL =>
>> '2147483647
>> > ',
>> > >> > >> >> KEEP_DELETED_CELLS => 'false', BLOCKSIZE
=> '16384',
>> IN_MEMORY
>> > =>
>> > >> > >> 'false',
>> > >> > >> >> ENCODE_ON_DISK => 'true', BLOCKCACHE =>
'true'}]}
>> > >> > >> >>
>> > >> > >> >> When the data size is around 100GB (100 Million
records),
>> then
>> > the
>> > >> > >> >> latency is very good. I am getting a throughput
of around
>> 300K
>> > >> OPS.
>> > >> > >> >> In both cases (100 GB and 1.8 TB) Ganglia stats
show that
>> Disk
>> > >> reads
>> > >> > >> are
>> > >> > >> >> around 50-60 MB/s throughout the read cycle.
>> > >> > >> >>
>> > >> > >> >> Thanks,
>> > >> > >> >> Ramu
>> > >> > >> >>
>> > >> > >> >>
>> > >> > >> >> On Mon, Oct 7, 2013 at 2:21 PM, lars hofhansl
<
>> larsh@apache.org
>> > >
>> > >> > >> wrote:
>> > >> > >> >>
>> > >> > >> >>> Have you enabled short circuit reading?
See here:
>> > >> > >> >>> http://hbase.apache.org/book/perf.hdfs.html
>> > >> > >> >>>
>> > >> > >> >>> How's your data locality (shown on the RegionServer
UI
>> page).
>> > >> > >> >>>
>> > >> > >> >>>
>> > >> > >> >>> How much memory are you giving your RegionServers?
>> > >> > >> >>> If you reads are truly random and the data
set does not fit
>> > into
>> > >> the
>> > >> > >> >>> aggregate cache, you'll be dominated by
the disk and
>> network.
>> > >> > >> >>> Each read would need to bring in a 64k (default)
HFile
>> block.
>> > If
>> > >> > short
>> > >> > >> >>> circuit reading is not enabled you'll get
two or three
>> context
>> > >> > >> switches.
>> > >> > >> >>>
>> > >> > >> >>> So I would try:
>> > >> > >> >>> 1. Enable short circuit reading
>> > >> > >> >>> 2. Increase the block cache size per RegionServer
>> > >> > >> >>> 3. Decrease the HFile block size
>> > >> > >> >>> 4. Make sure your data is local (if it is
not, issue a major
>> > >> > >> compaction).
>> > >> > >> >>>
>> > >> > >> >>>
>> > >> > >> >>> -- Lars
>> > >> > >> >>>
>> > >> > >> >>>
>> > >> > >> >>>
>> > >> > >> >>> ________________________________
>> > >> > >> >>>  From: Ramu M S <ramu.malur@gmail.com>
>> > >> > >> >>> To: user@hbase.apache.org
>> > >> > >> >>> Sent: Sunday, October 6, 2013 10:01 PM
>> > >> > >> >>> Subject: HBase Random Read latency >
100ms
>> > >> > >> >>>
>> > >> > >> >>>
>> > >> > >> >>> Hi All,
>> > >> > >> >>>
>> > >> > >> >>> My HBase cluster has 8 Region Servers (CDH
4.4.0, HBase
>> > 0.94.6).
>> > >> > >> >>>
>> > >> > >> >>> Each Region Server is with the following
configuration,
>> > >> > >> >>> 16 Core CPU, 192 GB RAM, 800 GB SATA (7200
RPM) Disk
>> > >> > >> >>> (Unfortunately configured with RAID 1, can't
change this as
>> the
>> > >> > >> Machines
>> > >> > >> >>> are leased temporarily for a month).
>> > >> > >> >>>
>> > >> > >> >>> I am running YCSB benchmark tests on HBase
and currently
>> > >> inserting
>> > >> > >> around
>> > >> > >> >>> 1.8 Billion records.
>> > >> > >> >>> (1 Key + 7 Fields of 100 Bytes = 724 Bytes
per record)
>> > >> > >> >>>
>> > >> > >> >>> Currently I am getting a write throughput
of around 100K
>> OPS,
>> > but
>> > >> > >> random
>> > >> > >> >>> reads are very very slow, all gets have
more than 100ms or
>> more
>> > >> > >> latency.
>> > >> > >> >>>
>> > >> > >> >>> I have changed the following default configuration,
>> > >> > >> >>> 1. HFile Size: 16GB
>> > >> > >> >>> 2. HDFS Block Size: 512 MB
>> > >> > >> >>>
>> > >> > >> >>> Total Data size is around 1.8 TB (Excluding
the replicas).
>> > >> > >> >>> My Table is split into 128 Regions (No pre-splitting
used,
>> > >> started
>> > >> > >> with 1
>> > >> > >> >>> and grew to 128 over the insertion time)
>> > >> > >> >>>
>> > >> > >> >>> Taking some inputs from earlier discussions
I have done the
>> > >> > following
>> > >> > >> >>> changes to disable Nagle (In both Client
and Server
>> > >> hbase-site.xml,
>> > >> > >> >>> hdfs-site.xml)
>> > >> > >> >>>
>> > >> > >> >>> <property>
>> > >> > >> >>>   <name>hbase.ipc.client.tcpnodelay</name>
>> > >> > >> >>>   <value>true</value>
>> > >> > >> >>> </property>
>> > >> > >> >>>
>> > >> > >> >>> <property>
>> > >> > >> >>>   <name>ipc.server.tcpnodelay</name>
>> > >> > >> >>>   <value>true</value>
>> > >> > >> >>> </property>
>> > >> > >> >>>
>> > >> > >> >>> Ganglia stats shows large CPU IO wait (>30%
during reads).
>> > >> > >> >>>
>> > >> > >> >>> I agree that disk configuration is not ideal
for Hadoop
>> > cluster,
>> > >> but
>> > >> > >> as
>> > >> > >> >>> told earlier it can't change for now.
>> > >> > >> >>> I feel the latency is way beyond any reported
results so
>> far.
>> > >> > >> >>>
>> > >> > >> >>> Any pointers on what can be wrong?
>> > >> > >> >>>
>> > >> > >> >>> Thanks,
>> > >> > >> >>> Ramu
>> > >> > >> >>>
>> > >> > >> >>
>> > >> > >> >>
>> > >> > >> >
>> > >> > >>
>> > >> > >
>> > >> > >
>> > >> >
>> > >>
>> > >>
>> > >>
>> > >> --
>> > >> Bharath Vissapragada
>> > >> <http://www.cloudera.com>
>> > >>
>> > >
>> > >
>> >
>>
>
>

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