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Date: Wed, 31 Jul 2013 16:39:37 -0300
Message-ID: 
 <CADQCNffWA7gjyVDR3vvikVvPDBY=a1p9Z=XCTRWA6q5o23ARiA@mail.gmail.com>
Subject: Re: help on key design
From: Pablo Medina <pablomedina85@gmail.com>
To: user@hbase.apache.org
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Right. I was assuming the scenario where the region is splitted in two
balanced regions. Balanced in terms of requested keys. As you said,
introducing randonmness can give you more control over that.


2013/7/31 Michael Segel <msegel@segel.com>

> Really?
>
> You split the region that is hot. What's to stop all of the keys that the
> OP wants are still within the same region?  Not to mention... how do you
> control which region is on which region server?
>
> Just food for thought.
>
> If the OP is doing get()s, then he may want to consider taking the hash,
> truncating it to 4 bytes and prepending it to his key.  This should give
> him some randomness.
>
>
>
> On Jul 31, 2013, at 1:57 PM, Pablo Medina <pablomedina85@gmail.com> wrote:
>
> > If you split that one hot region and then move a half to another region
> > server then you will move the half of the load of that hot region server.
> > The set of hot keys then will be spread over 2 region servers instead of
> > one.
> >
> >
> > 2013/7/31 Michael Segel <msegel@segel.com>
> >
> >> 4 regions on 3 servers?
> >> I'd say that they were already balanced.
> >>
> >> The issue is that when they do their get(s) they are hitting one region.
> >> So more splits isn't the answer.
> >>
> >>
> >> On Jul 31, 2013, at 12:49 PM, Ted Yu <yuzhihong@gmail.com> wrote:
> >>
> >>> From the information Demian provided in the first email:
> >>>
> >>> bq. a table containing 20 million keys splitted automatically by HBase
> >> in 4
> >>> regions and balanced in 3 region servers
> >>>
> >>> I think the number of regions should be increased through (manual)
> >>> splitting so that the data is spread more evenly across servers.
> >>>
> >>> If the Get's are scattered across whole key space, there is some
> >>> optimization the client can do. Namely group the Get's by region
> boundary
> >>> and issue multi get per region.
> >>>
> >>> Please also refer to http://hbase.apache.org/book.html#rowkey.design,
> >>> especially 6.3.2.
> >>>
> >>> Cheers
> >>>
> >>> On Wed, Jul 31, 2013 at 10:14 AM, Dhaval Shah
> >>> <prince_mithibai@yahoo.co.in>wrote:
> >>>
> >>>> Looking at https://issues.apache.org/jira/browse/HBASE-6136 it seems
> >> like
> >>>> the 500 Gets are executed sequentially on the region server.
> >>>>
> >>>> Also 3k requests per minute = 50 requests per second. Assuming your
> >>>> requests take 1 sec (which seems really long but who knows) then you
> >> need
> >>>> atleast 50 threads/region server handlers to handle these. Defaults
> for
> >>>> that number on some older versions of hbase is 10 which means you are
> >>>> running out of threads. Which brings up the following questions -
> >>>> What version of HBase are you running?
> >>>> How many region server handlers do you have?
> >>>>
> >>>> Regards,
> >>>> Dhaval
> >>>>
> >>>>
> >>>> ----- Original Message -----
> >>>> From: Demian Berjman <dberjman@despegar.com>
> >>>> To: user@hbase.apache.org
> >>>> Cc:
> >>>> Sent: Wednesday, 31 July 2013 11:12 AM
> >>>> Subject: Re: help on key design
> >>>>
> >>>> Thanks for the responses!
> >>>>
> >>>>> why don't you use a scan
> >>>> I'll try that and compare it.
> >>>>
> >>>>> How much memory do you have for your region servers? Have you enabled
> >>>>> block caching? Is your CPU spiking on your region servers?
> >>>> Block caching is enabled. Cpu and memory dont seem to be a problem.
> >>>>
> >>>> We think we are saturating a region because the quantity of keys
> >> requested.
> >>>> In that case my question will be if asking 500+ keys per request is a
> >>>> normal scenario?
> >>>>
> >>>> Cheers,
> >>>>
> >>>>
> >>>> On Wed, Jul 31, 2013 at 11:24 AM, Pablo Medina <
> pablomedina85@gmail.com
> >>>>> wrote:
> >>>>
> >>>>> The scan can be an option if the cost of scanning undesired cells and
> >>>>> discarding them trough filters is better than accessing those keys
> >>>>> individually. I would say that as the number of 'undesired' cells
> >>>> decreases
> >>>>> the scan overall performance/efficiency gets increased. It all
> depends
> >> on
> >>>>> how the keys are designed to be grouped together.
> >>>>>
> >>>>> 2013/7/30 Ted Yu <yuzhihong@gmail.com>
> >>>>>
> >>>>>> Please also go over http://hbase.apache.org/book.html#perf.reading
> >>>>>>
> >>>>>> Cheers
> >>>>>>
> >>>>>> On Tue, Jul 30, 2013 at 3:40 PM, Dhaval Shah <
> >>>>> prince_mithibai@yahoo.co.in
> >>>>>>> wrote:
> >>>>>>
> >>>>>>> If all your keys are grouped together, why don't you use a scan
> with
> >>>>>>> start/end key specified? A sequential scan can theoretically be
> >>>> faster
> >>>>>> than
> >>>>>>> MultiGet lookups (assuming your grouping is tight, you can also use
> >>>>>> filters
> >>>>>>> with the scan to give better performance)
> >>>>>>>
> >>>>>>> How much memory do you have for your region servers? Have you
> enabled
> >>>>>>> block caching? Is your CPU spiking on your region servers?
> >>>>>>>
> >>>>>>> If you are saturating the resources on your *hot* region server
> then
> >>>>> yes
> >>>>>>> having more region servers will help. If no, then something else is
> >>>> the
> >>>>>>> bottleneck and you probably need to dig further
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>> Regards,
> >>>>>>> Dhaval
> >>>>>>>
> >>>>>>>
> >>>>>>> ________________________________
> >>>>>>> From: Demian Berjman <dberjman@despegar.com>
> >>>>>>> To: user@hbase.apache.org
> >>>>>>> Sent: Tuesday, 30 July 2013 4:37 PM
> >>>>>>> Subject: help on key design
> >>>>>>>
> >>>>>>>
> >>>>>>> Hi,
> >>>>>>>
> >>>>>>> I would like to explain our use case of HBase, the row key design
> and
> >>>>> the
> >>>>>>> problems we are having so anyone can give us a help:
> >>>>>>>
> >>>>>>> The first thing we noticed is that our data set is too small
> compared
> >>>>> to
> >>>>>>> other cases we read in the list and forums. We have a table
> >>>> containing
> >>>>> 20
> >>>>>>> million keys splitted automatically by HBase in 4 regions and
> >>>> balanced
> >>>>>> in 3
> >>>>>>> region servers. We have designed our key to keep together the set
> of
> >>>>> keys
> >>>>>>> requested by our app. That is, when we request a set of keys we
> >>>> expect
> >>>>>> them
> >>>>>>> to be grouped together to improve data locality and block cache
> >>>>>> efficiency.
> >>>>>>>
> >>>>>>> The second thing we noticed, compared to other cases, is that we
> >>>>>> retrieve a
> >>>>>>> bunch keys per request (500 aprox). Thus, during our peaks (3k
> >>>> requests
> >>>>>> per
> >>>>>>> minute), we have a lot of requests going to a particular region
> >>>> servers
> >>>>>> and
> >>>>>>> asking a lot of keys. That results in poor response times (in the
> >>>> order
> >>>>>> of
> >>>>>>> seconds). Currently we are using multi gets.
> >>>>>>>
> >>>>>>> We think an improvement would be to spread the keys (introducing a
> >>>>>>> randomized component on it) in more region servers, so each rs will
> >>>>> have
> >>>>>> to
> >>>>>>> handle less keys and probably less requests. Doing that way the
> multi
> >>>>>> gets
> >>>>>>> will be spread over the region servers.
> >>>>>>>
> >>>>>>> Our questions:
> >>>>>>>
> >>>>>>> 1. Is it correct this design of asking so many keys on each
> request?
> >>>>> (if
> >>>>>>> you need high performance)
> >>>>>>> 2. What about splitting in more region servers? It's a good idea?
> How
> >>>>> we
> >>>>>>> could accomplish this? We thought in apply some hashing...
> >>>>>>>
> >>>>>>> Thanks in advance!
> >>>>>>>
> >>>>>>
> >>>>>
> >>>>
> >>>>
> >>
> >>
>
>

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