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From Bryan Beaudreault <bbeaudrea...@hubspot.com>
Subject Re: experiencing high latency for few reads in HBase
Date Thu, 29 Aug 2013 17:55:26 GMT
If you lost a RS or otherwise moved a region around (hbase balancer?) then
it would throw off the locality.  You'll want to compact any time a region
moves for any reason (unless it moved to another RS with which it had
locality).  Try major compacting again now and see if the locality index
goes up to 100


On Thu, Aug 29, 2013 at 1:52 PM, Saurabh Yahoo <saurabh_ag@yahoo.com> wrote:

> Thanks Vlad.
>
> Quick question. I notice hdfsBlocksLocalityIndex is around 50 in all
> region servers.
>
> Does that could be a problem? If it is, how to solve that? We already ran
> the major compaction after ingesting the data.
>
> Thanks,
> Saurabh.
>
> On Aug 29, 2013, at 12:17 PM, Vladimir Rodionov <vrodionov@carrieriq.com>
> wrote:
>
> > Yes. HBase won't guarantee strict sub-second latency.
> >
> > Best regards,
> > Vladimir Rodionov
> > Principal Platform Engineer
> > Carrier IQ, www.carrieriq.com
> > e-mail: vrodionov@carrieriq.com
> >
> > ________________________________________
> > From: Saurabh Yahoo [saurabh_ag@yahoo.com]
> > Sent: Thursday, August 29, 2013 2:49 AM
> > To: user@hbase.apache.org
> > Cc: user@hbase.apache.org
> > Subject: Re: experiencing high latency for few reads in HBase
> >
> > Hi Vlad,
> >
> > We do have strict latency requirement as it is financial data requiring
> direct access from clients.
> >
> > Are you saying that it is not possible to achieve sub second latency
> using hbase (because it is based on java.) ?
> >
> >
> >
> >
> >
> >
> >
> > On Aug 28, 2013, at 8:10 PM, Vladimir Rodionov <vrodionov@carrieriq.com>
> wrote:
> >
> >> Increasing Java heap size will make latency worse, actually.
> >> You can't guarantee 1 sec max latency if run Java app (unless your heap
> size is much less than 1GB).
> >> I have never heard about strict maximum latency limit. Usually , its
> 99% , 99.9 or 99.99% query percentiles.
> >>
> >> You can greatly reduce your 99.xxx% percentile latency by storing you
> data in 2 replicas to two different region servers.
> >> Issue two read operations to those two region servers in parallel and
> get the first response. Probability theory states that  probability
> >> of two independent events (slow requests) is  the product of event's
> probabilities themselves.
> >>
> >>
> >> Best regards,
> >> Vladimir Rodionov
> >> Principal Platform Engineer
> >> Carrier IQ, www.carrieriq.com
> >> e-mail: vrodionov@carrieriq.com
> >>
> >> ________________________________________
> >> From: Saurabh Yahoo [saurabh_ag@yahoo.com]
> >> Sent: Wednesday, August 28, 2013 4:18 PM
> >> To: user@hbase.apache.org
> >> Subject: Re: experiencing high latency for few reads in HBase
> >>
> >> Thanks Kiru,
> >>
> >> Scan is not an option for our use cases.  Our read is pretty random.
> >>
> >> Any other suggestion to bring down the latency.
> >>
> >> Thanks,
> >> Saurabh.
> >>
> >>
> >> On Aug 28, 2013, at 7:01 PM, Kiru Pakkirisamy <
> kirupakkirisamy@yahoo.com> wrote:
> >>
> >>> Saurabh, we are able to 600K rowxcolumns in 400 msec. We have put what
> was a 40million row table as 400K rows and columns. We Get about 100 of the
> rows from this 400K , do quite a bit of calculations in the coprocessor
> (almost a group-order by) and return in this time.
> >>> Maybe should consider replacing the MultiGets with Scan with Filter. I
> like the FuzzyRowFilter even though you might need to match with exact key.
> It works only with fixed length key.
> >>> (I do have an issue right now, it is not scaling to multiple clients.)
> >>>
> >>> Regards,
> >>> - kiru
> >>>
> >>>
> >>> Kiru Pakkirisamy | webcloudtech.wordpress.com
> >>>
> >>>
> >>> ________________________________
> >>> From: Saurabh Yahoo <saurabh_ag@yahoo.com>
> >>> To: "user@hbase.apache.org" <user@hbase.apache.org>
> >>> Cc: "user@hbase.apache.org" <user@hbase.apache.org>
> >>> Sent: Wednesday, August 28, 2013 3:20 PM
> >>> Subject: Re: experiencing high latency for few reads in HBase
> >>>
> >>>
> >>> Thanks Kitu. We need less than 1 sec latency.
> >>>
> >>> We are using both muliGet and get.
> >>>
> >>> We have three concurrent clients running 10 threads each. ( that makes
> total 30 concurrent clients).
> >>>
> >>> Thanks,
> >>> Saurabh.
> >>>
> >>> On Aug 28, 2013, at 4:30 PM, Kiru Pakkirisamy <
> kirupakkirisamy@yahoo.com> wrote:
> >>>
> >>>> Right 4 sec is good.
> >>>> @Saurabh - so your read is - getting 20 out of 25 millions rows ?. Is
> this a Get or a Scan ?
> >>>> BTW, in this stress test how many concurrent clients do you have ?
> >>>>
> >>>> Regards,
> >>>> - kiru
> >>>>
> >>>>
> >>>> ________________________________
> >>>> From: Vladimir Rodionov <vrodionov@carrieriq.com>
> >>>> To: "user@hbase.apache.org" <user@hbase.apache.org>
> >>>> Sent: Wednesday, August 28, 2013 12:15 PM
> >>>> Subject: RE: experiencing high latency for few reads in HBase
> >>>>
> >>>>
> >>>> 1. 4 sec max latency is not that bad taking into account 12GB heap.
>  It can be much larger. What is your SLA?
> >>>> 2. Block evictions is the result of a poor cache hit rate and the
> root cause of a periodic stop-the-world GC pauses (max latencies
> >>>>    latencies you have been observing in the test)
> >>>> 3. Block cache consists of 3 parts (25% young generation, 50% -
> tenured, 25% - permanent). Permanent part is for CF with
> >>>> IN_MEMORY = true (you can specify this when you create CF).  Block
> first stored in 'young gen' space, then gets promoted to 'tenured gen' space
> >>>> (or gets evicted). May be your 'perm gen' space is underutilized?
> This is exact 25% of 4GB (1GB). Although HBase LruBlockCache should use all
> the space allocated for block cache -
> >>>> there is no guarantee (as usual). If you don have in_memory column
> families you may decrease
> >>>>
> >>>>
> >>>>
> >>>> Best regards,
> >>>> Vladimir Rodionov
> >>>> Principal Platform Engineer
> >>>> Carrier IQ, www.carrieriq.com
> >>>> e-mail: vrodionov@carrieriq.com
> >>>>
> >>>> ________________________________________
> >>>> From: Saurabh Yahoo [saurabh_ag@yahoo.com]
> >>>> Sent: Wednesday, August 28, 2013 5:10 AM
> >>>> To: user@hbase.apache.org
> >>>> Subject: experiencing high latency for few reads in HBase
> >>>>
> >>>> Hi,
> >>>>
> >>>> We are running a stress test in our 5 node cluster and we are getting
> the expected mean latency of 10ms. But we are seeing around 20 reads out of
> 25 million reads having latency more than 4 seconds. Can anyone provide the
> insight what we can do to meet below second SLA for each and every read?
> >>>>
> >>>> We observe the following things -
> >>>>
> >>>> 1. Reads are evenly distributed among 5 nodes.  CPUs remain under 5%
> utilized.
> >>>>
> >>>> 2. We have 4gb block cache (30% block cache out of 12gb) setup. 3gb
> block cache got filled up but around 1gb remained free. There are a large
> number of cache eviction.
> >>>>
> >>>> Questions to experts -
> >>>>
> >>>> 1. If there are still 1gb of free block cache available, why is hbase
> evicting the block from cache?
> >>>>
> >>>> 4. We are seeing memory went up to 10gb three times before dropping
> sharply to 5gb.
> >>>>
> >>>> Any help is highly appreciable,
> >>>>
> >>>> Thanks,
> >>>> Saurabh.
> >>>>
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