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	<E403FDF7-B908-410F-9D0C-CEFD6861EF2C@thelastpickle.com>
Date: Mon, 27 Jun 2011 18:08:01 -0700
Message-ID: <BANLkTiknEjXffzx0x1gExkVw-6KHC2JxnA@mail.gmail.com>
Subject: Re: Clock skew
From: Yang <teddyyyy123@gmail.com>
To: user@cassandra.apache.org
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oftentimes people use time actually subconsciously to express causal
relations ("before/after"), as long as you have some other means to
establish causal relations, you don't really need to have an exactly clock.

On Mon, Jun 27, 2011 at 4:54 PM, aaron morton <aaron@thelastpickle.com>wrote:

> Without exception the timestamp is set by the client, not the server. The
> one exception to the without exception rule is CounterColumnType operations.
>
> If you are in a situation where you need better timing than you can get
> with ntp you should try to design around it.
>
> Hope that helps.
> -----------------
> Aaron Morton
> Freelance Cassandra Developer
> @aaronmorton
> http://www.thelastpickle.com
>
> On 28 Jun 2011, at 10:03, A J wrote:
>
> > During writes, the timestamp field in the column is the system-time of
> > that node (correct me if that is not the case and the system-time of
> > the co-ordinator is what gets applied to all the replicas).
> > During reads, the latest write wins.
> >
> > What if there is a clock skew ? It could lead to a stale write
> > over-riding the actual latest write, just because the clock of that
> > node is ahead of the other node. Right ?
>
>

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oftentimes people use time actually subconsciously to express causal relati=
ons (&quot;before/after&quot;), as long as you have some other means to=A0<=
div>establish causal relations, you don&#39;t really need to have an exactl=
y clock.<br>
<br><div class=3D"gmail_quote">On Mon, Jun 27, 2011 at 4:54 PM, aaron morto=
n <span dir=3D"ltr">&lt;<a href=3D"mailto:aaron@thelastpickle.com">aaron@th=
elastpickle.com</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote" =
style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
Without exception the timestamp is set by the client, not the server. The o=
ne exception to the without exception rule is CounterColumnType operations.=
<br>
<br>
If you are in a situation where you need better timing than you can get wit=
h ntp you should try to design around it.<br>
<br>
Hope that helps.<br>
-----------------<br>
<font color=3D"#888888">Aaron Morton<br>
Freelance Cassandra Developer<br>
@aaronmorton<br>
<a href=3D"http://www.thelastpickle.com" target=3D"_blank">http://www.thela=
stpickle.com</a><br>
</font><div><div></div><div class=3D"h5"><br>
On 28 Jun 2011, at 10:03, A J wrote:<br>
<br>
&gt; During writes, the timestamp field in the column is the system-time of=
<br>
&gt; that node (correct me if that is not the case and the system-time of<b=
r>
&gt; the co-ordinator is what gets applied to all the replicas).<br>
&gt; During reads, the latest write wins.<br>
&gt;<br>
&gt; What if there is a clock skew ? It could lead to a stale write<br>
&gt; over-riding the actual latest write, just because the clock of that<br=
>
&gt; node is ahead of the other node. Right ?<br>
<br>
</div></div></blockquote></div><br></div>

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