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Date: Tue, 3 Jun 2014 10:52:13 -0700
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Subject: Re: Multi-DC Environment Question
From: Robert Coli <rcoli@eventbrite.com>
To: "user@cassandra.apache.org" <user@cassandra.apache.org>
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On Fri, May 30, 2014 at 4:08 AM, Vasileios Vlachos <
vasileiosvlachos@gmail.com> wrote:

> Basically you sort of confirmed that if down_time > max_hint_window_in_ms
> the only way to bring DC1 up-to-date is anti-entropy repair.
>

Also, read repair does not help either as we assumed that down_time >
> max_hint_window_in_ms. Please correct me if I am wrong.
>

My understanding is that if you :

1) set read repair chance to 100%
2) read all keys in the keyspace with a client

You would accomplish the same increase in consistency as you would by
running repair.

In cases where this may matter, and your system can handle delivering the
hints, increasing the already-increased-from-old-default-of-1-hour current
default of 3 hours to 6 or more hours gives operators more time to work in
the case of partition or failure. Note that hints are only an optimization,
only repair (and read repair at 100%, I think..) assert any guarantee of
consistency.

=Rob

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<div dir=3D"ltr"><div class=3D"gmail_extra"><div class=3D"gmail_quote">On F=
ri, May 30, 2014 at 4:08 AM, Vasileios Vlachos <span dir=3D"ltr">&lt;<a hre=
f=3D"mailto:vasileiosvlachos@gmail.com" target=3D"_blank">vasileiosvlachos@=
gmail.com</a>&gt;</span> wrote:<br>

<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex"><div dir=3D"ltr"><div>Basically you sort of =
confirmed that if down_time &gt; max_hint_window_in_ms the only way to brin=
g DC1 up-to-date is anti-entropy repair.=C2=A0</div>

</div></blockquote><div><br></div><blockquote class=3D"gmail_quote" style=
=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir=
=3D"ltr"><div>Also, read repair does not help either as we assumed that dow=
n_time &gt; max_hint_window_in_ms. Please correct me if I am wrong.</div>

</div></blockquote><div><br></div><div>My understanding is that if you :</d=
iv><div><br></div><div>1) set read repair chance to 100%</div><div>2) read =
all keys in the keyspace with a client</div><div><br></div><div>You would a=
ccomplish the same increase in consistency as you would by running repair.<=
/div>

<div><br></div><div>In cases where this may matter, and your system can han=
dle delivering the hints, increasing the already-increased-from-old-default=
-of-1-hour current default of 3 hours to 6 or more hours gives operators mo=
re time to work in the case of partition or failure. Note that hints are on=
ly an optimization, only repair (and read repair at 100%, I think..) assert=
 any guarantee of consistency.</div>

<div><br></div><div>=3DRob</div><div><br></div></div></div></div>

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