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Date: Tue, 23 Aug 2011 13:06:13 -0400
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 <CAENxBwwGvUwV0PDTRQugfM85=UnSiiOLmHBzZoRM2CAzvtN7=A@mail.gmail.com>
Subject: Re: how to know if nodetool cleanup is safe?
From: Edward Capriolo <edlinuxguru@gmail.com>
To: user@cassandra.apache.org
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On Tue, Aug 23, 2011 at 11:56 AM, Sam Overton <soverton@acunu.com> wrote:

> On 21 August 2011 12:34, Yan Chunlu <springrider@gmail.com> wrote:
>
>> since "nodetool cleanup" could remove hinted handoff,  will it cause the
>> data loss?
>
>
> Hi Yan,
>
> Hints are not guaranteed to be delivered and "nodetool cleanup" is one of
> the reasons for that. This will only cause data-loss if you are writing at
> CL.ANY where a hint counts as a write. If you are writing at CL.ONE or above
> then at least one replica must receive the data for the write to succeed, so
> losing hints will not cause data-loss.
>
> If a hint is not delivered then the replica to which it was intended will
> become consistent after a read-repair, or after manual anti-entropy repair.
>
> Sam
>
> --
> Sam Overton
> Acunu | http://www.acunu.com | @acunu
>

If you run nodetool tpstats on each node in your cluster and ensure none of
them have an active or pending threads in the Hinted stage no hints are
currently being delivered. But as pointed out above Hinted Handoff is a best
effort system.

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<br><div class=3D"gmail_quote">On Tue, Aug 23, 2011 at 11:56 AM, Sam Overto=
n <span dir=3D"ltr">&lt;<a href=3D"mailto:soverton@acunu.com">soverton@acun=
u.com</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote" style=3D"m=
argin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div class=3D"gmail_quote">On 21 August 2011 12:34, Yan Chunlu <span dir=3D=
"ltr">&lt;<a href=3D"mailto:springrider@gmail.com" target=3D"_blank">spring=
rider@gmail.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">

since &quot;nodetool cleanup&quot; could remove hinted handoff, =A0will it =
cause the data loss?
</blockquote></div><div><br></div>Hi Yan,<div><br></div><div>Hints are not =
guaranteed to be delivered and &quot;nodetool cleanup&quot; is one of the r=
easons for that. This will only cause data-loss if you are writing at CL.AN=
Y where a hint counts as a write. If you are writing at CL.ONE or above the=
n at least one replica must receive the data for the write to succeed, so l=
osing hints will not cause data-loss.=A0</div>

<div><br></div><div>If a hint is not delivered then the replica to which it=
 was intended will become consistent after a read-repair, or after manual a=
nti-entropy repair.</div><div><br></div><div>Sam<div><div><br></div><font c=
olor=3D"#888888">-- <br>

<span style=3D"border-collapse:collapse;color:rgb(136, 136, 136);font-famil=
y:arial, sans-serif;font-size:13px">Sam Overton<br>Acunu |=A0<a href=3D"htt=
p://www.acunu.com/" style=3D"color:rgb(0, 0, 204)" target=3D"_blank">http:/=
/www.acunu.com</a>=A0| @acunu</span><br>


</font></div></div>
</blockquote></div><div><br></div><div>If you run nodetool tpstats on each =
node in your cluster and ensure none of them have an active or pending thre=
ads in the Hinted stage no hints are currently being delivered. But as poin=
ted out above Hinted Handoff is a best effort system. =A0</div>

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