Mailing-List: contact user-help@hbase.apache.org; run by ezmlm
Precedence: bulk
Reply-To: user@hbase.apache.org
Received-SPF: pass (athena.apache.org: domain of anoopsj@huawei.com designates
 119.145.14.65 as permitted sender)
From: Anoop Sam John <anoopsj@huawei.com>
To: "user@hbase.apache.org" <user@hbase.apache.org>
Subject: RE: Isolation level
Thread-Topic: Isolation level
Thread-Index: AQHNSu82GSRudLHyD0KKvcl4+II585b7CdMAgARmFOqAAAQngIAAkjY2
Date: Mon, 18 Jun 2012 13:11:50 +0000
Message-ID: 
 <0CE69E9126D0344088798A3B7F7F8086311332AC@szxeml531-mbx.china.huawei.com>
References: 
 <loom.20120615T131535-129@post.gmane.org>,<CAG+ckK8ZoD42VDwwmXrF5dhxGaCy0Fh_FtwHf30n7koYVeRRUg@mail.gmail.com>
 <0CE69E9126D0344088798A3B7F7F80863112ED91@szxeml531-mbx.china.huawei.com>,<BLU0-SMTP1173C8C6E815284FA93B9C78FF80@phx.gbl>
In-Reply-To: <BLU0-SMTP1173C8C6E815284FA93B9C78FF80@phx.gbl>
Accept-Language: en-US, zh-CN
Content-Language: en-US
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0

Hi

A put operation HBase may need to write data to multiple stores. [Depends o=
n presence of  KVs belonging to different CFs in the Put]
A put can be considered as committed when it has successfully done the writ=
e to all the corresponding stores [In turn into the Memstores of those stor=
es]

In case of a READ_UNCOMMITTED level, there can be situation of partial row =
read. At the time of read the write was completed in one store but not in a=
nother.
The read committed level makes sure this will not happen using the MVCC.


-Anoop-
________________________________________
From: Michael Segel [michael_segel@hotmail.com]
Sent: Monday, June 18, 2012 5:16 PM
To: user@hbase.apache.org
Subject: Re: Isolation level

Since you don't have OLTP,  the terms need to be better defined.
What is meant by an uncommitted_ write in HBase?

RLL in RDBMS is different than RLL in HBase. You don't have the concept of =
a transaction in HBase.

-Mike


On Jun 17, 2012, at 10:32 PM, Anoop Sam John wrote:

> Hi
>           You can check Scan#setIsolationLevel() API for changing the lev=
el. By default it is  read committed means read only committed writes.
>
> -Anoop-
> ________________________________________
> From: Jerry Lam [chilinglam@gmail.com]
> Sent: Friday, June 15, 2012 9:51 PM
> To: user@hbase.apache.org
> Subject: Re: Isolation level
>
> Hi Cristina:
>
> My understanding of HBase is that the isolation level fro read ops is Rea=
d
> Committed. There is only write lock which could protect the data from
> modifying by other requests but there is no read-lock (it is there but it
> doesn't have any effect). Since put ops are atomic, it can succeed or fai=
l
> but not in the middle so clients can only read the data if the write ops
> succeeds
>
> HTH,
>
> Jerry
>
>
> On Fri, Jun 15, 2012 at 7:59 AM, Cristina <cristi_p_r@hotmail.com> wrote:
>
>> Hi,
>>
>> I have read that Hbase has read committed as isolation level, but I have
>> some
>> doubts.
>> Is it possible to chage this level, for instance to read uncommitted? Ho=
w
>> could
>> I do this?
>> Another question, Is this isolation level based on locks? I have doubts
>> because
>> Hbase has multiversion concurrency control so it may implement read
>> committed
>> snapshot or snapshot isolation.
>>
>> Thanks,
>>   Cristina
>>
>>=