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Date: Thu, 19 May 2011 12:14:04 -0700
Message-ID: <BANLkTinaS6J=4dx6dhAHaU_ZoYSQDfgVJg@mail.gmail.com>
Subject: Re: Reading from client buffer
From: Jean-Daniel Cryans <jdcryans@apache.org>
To: dev@hbase.apache.org
Content-Type: text/plain; charset=ISO-8859-1

The write buffer is a hack for faster write performance during bulk
loads, no one should use it in a situation like you described.

Even if the client was able to read from it's own buffer, the edits
didn't make it to the region server so the other clients wouldn't be
able to see that new data either. Now let's suppose the client died
before flushing, well you would be serving data that actually never
existed!

I think we should just fix the documentation.

J-D

On Thu, May 19, 2011 at 8:02 AM, fazool mein <fazoolmein@gmail.com> wrote:
> Hi,
>
> I am going through the Hbase code to understand its properties better.
>
> There is something called 'write buffer' on the client side. Say it is
> enabled. Now, assume a client puts value v under key k, and immediately
> reads k.
>
> As I understand from the code, the put will be stored in the client side
> write buffer, while the read will go to the region server, returing an older
> value, instead of v.
>
> Doesn't this violate the ACID semantics (visibility in particular ) of Hbase
> given at: http://hbase.apache.org/acid-semantics.html
>
> <quote>
>
> When a client receives a "success" response for any mutation, that mutation
> is immediately visible to both that client and any client with whom it later
> communicates through side channels.
>
> </quote>
>
> Thanks.
>
> Regards
>