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From Aaron Zimmerman <azimmer...@sproutsocial.com>
Subject Re: writing and reading from a region at once
Date Mon, 29 Apr 2013 18:31:26 GMT
Perfect - The readPoint / WriteNumber stuff looks like what I was looking for. 

thanks!

AZ


On Apr 29, 2013, at 11:26 AM, ramkrishna vasudevan <ramkrishna.s.vasudevan@gmail.com>
wrote:

> Check this out
> http://www.slideshare.net/cloudera/3-learning-h-base-internals-lars-hofhansl-salesforce-final
> 
> Regards
> Ram
> 
> 
> On Mon, Apr 29, 2013 at 7:59 PM, Aaron Zimmerman <
> azimmerman@sproutsocial.com> wrote:
> 
>> Thanks J-D.  I'm interested in learning how HBase handles MVCC - do you
>> know of any resources explaining?  I have data streaming into hbase around
>> 6 million records a day, and I'm scanning the tables pretty much constantly
>> with mapreduce jobs that rollup and store the data elsewhere.  So I want to
>> understand better exactly which rows are present in a given scan.
>> 
>> If I create a scan that reads an entire region, I would expect a "read
>> committed" level to lock that region during the read (which might take a
>> few minutes).    So what happens to the rows that are inserted during the
>> scan?
>> 
>> AZ
>> 
>> 
>> On Apr 25, 2013, at 4:34 PM, Jean-Daniel Cryans <jdcryans@apache.org>
>> wrote:
>> 
>>> Inline.
>>> 
>>> J-D
>>> 
>>> 
>>> On Thu, Apr 25, 2013 at 1:09 PM, Aaron Zimmerman <
>>> azimmerman@sproutsocial.com> wrote:
>>> 
>>>> Hi,
>>>> 
>>>> If a region is being written to, and a scanner takes a lease out on the
>>>> region, what will happen to the writes?  Is there a concept of
>> "Transaction
>>>> Isolation Levels"?
>>>> 
>>> 
>>> There's MVCC, so reads can happen while someone else is writing. What you
>>> should expect from HBase is "read committed".
>>> 
>>> 
>>>> 
>>>> I don't see errors in Puts while the tables are being scanned?  But it
>>>> seems that I'm losing writes somewhere, is it possible the writes could
>>>> fail silently?
>>>> 
>>> 
>>> Is it temporary while you're scanning or there's really data missing at
>>> the end of the day? The former might happen on some older HBase versions
>>> while the latter should never happen unless you lower the durability
>> level
>>> yourself and have machine failures.
>>> 
>>> J-D
>> 
>> 


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