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From Saurabh Yahoo <saurabh...@yahoo.com>
Subject Re: experiencing high latency for few reads in HBase
Date Wed, 28 Aug 2013 23:18:10 GMT
Thanks Kiru,

Scan is not an option for our use cases.  Our read is pretty random.

Any other suggestion to bring down the latency.   


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
> 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
>> 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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