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 the.wa.syndrome@gmail.com
 designates 209.85.161.172 as permitted sender)
MIME-Version: 1.0
In-Reply-To: <loom.20120528T231829-822@post.gmane.org>
References: <loom.20120528T231829-822@post.gmane.org>
Date: Wed, 30 May 2012 10:44:11 +0100
Message-ID: 
 <CABOR7TcLuuRqa55fTuqj3pT3cm=T+OeZX_HUxHYpDHsNLMpg9g@mail.gmail.com>
Subject: Re: Concurrency Control
From: =?UTF-8?Q?Filipe_Gon=C3=A7alves?= <the.wa.syndrome@gmail.com>
To: user@cassandra.apache.org
Content-Type: multipart/alternative; boundary=bcaec5299a31213d7504c13dcb0b

--bcaec5299a31213d7504c13dcb0b
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

It's the timestamps provided in the columns that do concurrency
control/conflict resolution. Basically, the newer timestamp wins.
For counters I think there is no such mechanism (i.e. counter updates are
not idempotent).

>From https://wiki.apache.org/cassandra/DataModel :

All values are supplied by the client, including the 'timestamp'. This
> means that clocks on the clients should be synchronized (in the Cassandra
> server environment is useful also), as these timestamps are used for
> conflict resolution. In many cases the 'timestamp' is not used in client
> applications, and it becomes convenient to think of a column as a
> name/value pair. For the remainder of this document, 'timestamps' will be
> elided for readability. It is also worth noting the name and value are
> binary values, although in many applications they are UTF8 serialized
> strings.
> Timestamps can be anything you like, but microseconds since 1970 is a
> convention. Whatever you use, it must be consistent across the applicatio=
n,
> otherwise earlier changes may overwrite newer ones.


2012/5/28 Helen <live42day@gmx.ch>

> Hi,
> what kind of Concurrency Control Method is used in Cassandra? I found out
> so far
> that it's not done with the MVCC Method and that no vector clocks are
> being used.
> Thanks Helen
>
>


--=20
Filipe Gon=C3=A7alves

--bcaec5299a31213d7504c13dcb0b
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

<div>It&#39;s the timestamps provided in the columns that do concurrency co=
ntrol/conflict resolution. Basically, the newer timestamp wins.</div><div>F=
or counters I think there is no such mechanism (i.e. counter updates are no=
t idempotent).</div>
<div><br></div>From=C2=A0<a href=3D"https://wiki.apache.org/cassandra/DataM=
odel">https://wiki.apache.org/cassandra/DataModel</a>=C2=A0:<div><br></div>=
<div><blockquote class=3D"gmail_quote" style=3D"margin-top:0px;margin-right=
:0px;margin-bottom:0px;margin-left:0.8ex;border-left-width:1px;border-left-=
color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
All values are supplied by the client, including the &#39;timestamp&#39;. T=
his means that clocks on the clients should be synchronized (in the Cassand=
ra server environment is useful also), as these timestamps are used for con=
flict resolution. In many cases the &#39;timestamp&#39; is not used in clie=
nt applications, and it becomes convenient to think of a column as a name/v=
alue pair. For the remainder of this document, &#39;timestamps&#39; will be=
 elided for readability. It is also worth noting the name and value are bin=
ary values, although in many applications they are UTF8 serialized strings.=
<br>
Timestamps can be anything you like, but microseconds since 1970 is a conve=
ntion. Whatever you use, it must be consistent across the application, othe=
rwise earlier changes may overwrite newer ones.</blockquote><p class=3D"lin=
e874" style=3D"font-family:sans-serif;background-color:rgb(255,255,255)">
<span class=3D"anchor" id=3D"line-39"></span></p><br><div class=3D"gmail_qu=
ote">2012/5/28 Helen <span dir=3D"ltr">&lt;<a href=3D"mailto:live42day@gmx.=
ch" target=3D"_blank">live42day@gmx.ch</a>&gt;</span><br><blockquote class=
=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padd=
ing-left:1ex">
Hi,<br>
what kind of Concurrency Control Method is used in Cassandra? I found out s=
o far<br>
that it&#39;s not done with the MVCC Method and that no vector clocks are b=
eing used.<br>
Thanks Helen<br>
<br>
</blockquote></div><br><br clear=3D"all"><div><br></div>-- <br>Filipe Gon=
=C3=A7alves<br>
</div>

--bcaec5299a31213d7504c13dcb0b--