Mailing-List: contact user-help@cassandra.apache.org; run by ezmlm
Precedence: bulk
Reply-To: user@cassandra.apache.org
Received-SPF: pass (nike.apache.org: domain of felipefsch@gmail.com designates
 209.85.213.44 as permitted sender)
MIME-Version: 1.0
In-Reply-To: <C4E2EC5C-6801-475D-96B8-583D381DD0FC@thelastpickle.com>
References: 
 <CAP_qDpwYWTM+WYUeG5YC0m2N-z6ms2A1HAmwUXpexnd=Orty+g@mail.gmail.com>
	<201205141035386232944@software.ict.ac.cn>
	<CAP_qDpztSs4=1sHGHZoq9MDpgNvHhCTn4j-MVrLZNQ+=P_w+9A@mail.gmail.com>
	<C4E2EC5C-6801-475D-96B8-583D381DD0FC@thelastpickle.com>
Date: Wed, 16 May 2012 16:16:26 +0200
Message-ID: 
 <CAP_qDpxpDpa8YqfZnxf5KYm3AksE79dqWpwBAejZQpZbYrV6fw@mail.gmail.com>
Subject: Re: Retrieving old data version for a given row
From: Felipe Schmidt <felipefsch@gmail.com>
To: user@cassandra.apache.org
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

That was very helpfull, thank you very much!

I still have some questions:
-it is possible to make Cassandra keep old value data after flushing?
The same question for the memTable, before flushing. Seems to me that
when I update some tuple, the old data will be overwrited in memTable,
even before flushing.
-it is possible to scan values from the memtable, maybe using the
so-called Thrift API? Using the client-api I can just see the newest
data version, I can't see what's really happening with the memTable.

I ask that cause what I'll try to do is a Change Data Capture to
Cassandra and the answers will define what kind of aproaches I'm able
to use.

Thanks in advance.

Regards,
Felipe Mathias Schmidt
(Computer Science UFRGS, RS, Brazil)


2012/5/14 aaron morton <aaron@thelastpickle.com>:
> Cassandra does not provide access to multiple versions of the same column=
.
> It is essentially implementation detail.
>
> All mutations are written to the commit log in a binary format, see the
> o.a.c.db.RowMutation.getSerializedBuffer() (If you want to tail it for
> analysis you may want to change=A0commitlog_sync in cassandra.yaml)
>
> Here is post about looking at multiple versions columns in an
> sstable=A0http://thelastpickle.com/2011/05/15/Deletes-and-Tombstones/
>
> Remember that not all "versions" of a column are written to disk
> =A0(see=A0http://thelastpickle.com/2011/04/28/Forces-of-Write-and-Read/).=
=A0Also
> compaction will compress multiple versions of the same column from multip=
le
> files into a single version in a single file .
>
> Hope that helps.
>
>
> -----------------
> Aaron Morton
> Freelance Developer
> @aaronmorton
> http://www.thelastpickle.com
>
> On 14/05/2012, at 9:50 PM, Felipe Schmidt wrote:
>
> Yes, I need this information just for academic purposes.
>
> So, to read old data values, I tried to open the Commitlog using tail
> -f and also the log files viewer of Ubuntu, but I can not see many
> informations inside of the log!
> Is there any other way to open this log? I didn't find any Cassandra
> API for this purpose.
>
> Thanks averybody in advance.
>
> Regards,
> Felipe Mathias Schmidt
> (Computer Science UFRGS, RS, Brazil)
>
>
>
>
> 2012/5/14 zhangcheng2 <zhangcheng2@software.ict.ac.cn>:
>
> After compaciton, the old version data will gone!
>
>
> ________________________________
>
> zhangcheng2
>
>
> From:=A0Felipe Schmidt
>
> Date:=A02012-05-14=A005:33
>
> To:=A0user
>
> Subject:=A0Retrieving old data version for a given row
>
> I'm=A0trying=A0to=A0retrieve=A0old=A0data=A0version=A0for=A0some=A0row=A0=
but=A0it=A0seems=A0not
>
> be=A0possible.=A0I'm=A0a=A0beginner=A0=A0with=A0Cassandra=A0and=A0the=A0u=
nique=A0aproach=A0I
>
> know=A0is=A0looking=A0to=A0the=A0SSTable=A0in=A0the=A0storage=A0folder,=
=A0but=A0if=A0I=A0insert
>
> some=A0column=A0and=A0right=A0after=A0insert=A0another=A0value=A0to=A0the=
=A0same=A0row,
>
> after=A0flushing,=A0I=A0only=A0get=A0the=A0last=A0value.
>
> Is=A0there=A0any=A0way=A0to=A0get=A0the=A0old=A0data=A0version?=A0Obvious=
ly,=A0before=A0compaction.
>
>
> Regards,
>
> Felipe=A0Mathias=A0Schmidt
>
> (Computer=A0Science=A0UFRGS,=A0RS,=A0Brazil)
>
>
>