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 edlinuxguru@gmail.com
 designates 209.85.210.174 as permitted sender)
MIME-Version: 1.0
In-Reply-To: 
 <CAEONjQLUoNRXT2fQPb9eHtoorTgrZR9xoPnK8HG+Ct0n3QoXHQ@mail.gmail.com>
References: 
 <CAEXp8=xywukKOo0AT+HnMJF0Fkad3S=-HPQtfEbjCm469xfXVg@mail.gmail.com>
	<CAOG6zs0-dinHZdMaa21WuB1C74AEkWD2kfV6dS3Le_WNWw=zgA@mail.gmail.com>
	<CAAam9supQrtwEasWTOHy3LahqZZta6MFxtPh4Nf8+ob2L6baog@mail.gmail.com>
	<CAEONjQLUoNRXT2fQPb9eHtoorTgrZR9xoPnK8HG+Ct0n3QoXHQ@mail.gmail.com>
Date: Mon, 10 Dec 2012 10:00:28 -0500
Message-ID: 
 <CAENxBwxt--H5cA6AVe8aoWyYcF5n1E6o=fP0+N2uPwqRd0kBZQ@mail.gmail.com>
Subject: Re: Virtual Nodes, lots of physical nodes and potentially increasing
 outage count?
From: Edward Capriolo <edlinuxguru@gmail.com>
To: user@cassandra.apache.org
Content-Type: multipart/alternative; boundary=e89a8f64671777247304d080d399

--e89a8f64671777247304d080d399
Content-Type: text/plain; charset=ISO-8859-1

Assuming you need to work with quorum in a non-vnode scenario. That means
that if 2 nodes in a row in the ring are down some number of quorum
operations will fail with UnavailableException (TimeoutException right
after the failures). This is because the for a given range of tokens quorum
will be impossible, but quorum will be possible for others.

In a vnode world if any two nodes are down,  then the intersection of vnode
token ranges they have are unavailable.

I think it is two sides of the same coin.


On Mon, Dec 10, 2012 at 7:41 AM, Richard Low <rlow@acunu.com> wrote:

> Hi Tyler,
>
> You're right, the math does assume independence which is unlikely to be
> accurate.  But if you do have correlated failure modes e.g. same power,
> racks, DC, etc. then you can still use Cassandra's rack-aware or DC-aware
> features to ensure replicas are spread around so your cluster can survive
> the correlated failure mode.  So I would expect vnodes to improve uptime in
> all scenarios, but haven't done the math to prove it.
>
> Richard.
>

--e89a8f64671777247304d080d399
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

<div>Assuming you need to work with quorum in a non-vnode scenario. That me=
ans that if 2 nodes in a row in the ring are down some number of quorum ope=
rations will fail with UnavailableException (TimeoutException right after t=
he failures). This is because the for a given range of tokens quorum will b=
e impossible, but quorum will be possible for others.</div>
<div><br></div><div>In a vnode world if any two nodes are down, =A0then the=
 intersection of vnode token ranges they have are unavailable.=A0</div><div=
><br></div><div>I think it is two sides of the same coin.=A0</div><div><br>=
</div>
<br><div class=3D"gmail_quote">On Mon, Dec 10, 2012 at 7:41 AM, Richard Low=
 <span dir=3D"ltr">&lt;<a href=3D"mailto:rlow@acunu.com" target=3D"_blank">=
rlow@acunu.com</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote" s=
tyle=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div id=3D":45n">Hi Tyler,<div><br></div><div>You&#39;re right, the math do=
es assume independence which is unlikely to be accurate. =A0But if you do h=
ave correlated failure modes e.g. same power, racks, DC, etc. then you can =
still use Cassandra&#39;s rack-aware or DC-aware features to ensure replica=
s are spread around so your cluster can survive the correlated failure mode=
. =A0So I would expect vnodes to improve uptime in all scenarios, but haven=
&#39;t done the math to prove it.</div>


<div><br></div><div>Richard.</div></div></blockquote></div><br>

--e89a8f64671777247304d080d399--