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From Paulo Ricardo Motta Gomes <>
Subject Re: repair takes 10x more time in one DC compared to the other
Date Wed, 25 Jun 2014 16:11:25 GMT
Thanks for the explanation, but I got slightly confused:

>From my understanding, you just described the behavior of the
-pr/--partitioner-range option: "Repair only the first range returned by
the partitioner for the node." , so I would understand that repairs in the
same CFs in different DCs with only the -pr option could take different

However according to the description of the -local/--in-local-dc option, it
"only repairs against nodes in the same data center", but you said that "the
range will be repaired for all replica in all data-centers", even with the
"-local" option, or did you confuse it with "-pr" option?

In any case, I'm using both "-local" and "-pr" options, what is the
expected behavior in that case?


On Wed, Jun 25, 2014 at 12:46 PM, Sylvain Lebresne <>

> TL;DR, this is not unexpected and this is perfectly fine.
> For every node, 'repair --local' will repair the "primary" (where primary
> means "the first range on the ring picked by the consistent hashing for
> this node given its token", nothing more) range of the node in the ring.
> And that range will be repaired for all replica in all data-centers. When
> you assign tokens to multiple DC, it's actually pretty common to offset the
> tokens of one DC slightly compared to the other one. This will result in
> the "primary" ranges being always small in one DC but not the other. But
> please note that this perfectly ok, it does not imply any imbalance in
> data-centers. It also don't really mean that the node of one DC actually do
> a lot more work than the other ones: all nodes most likely contribute
> roughly the same amount of work to the repair. It only mean that the nodes
> of one DC "coordinate" more repair work that those of the other DC. Which
> is not really a big deal since coordinating a repair is cheap.
> --
> Sylvain
> On Wed, Jun 25, 2014 at 4:43 PM, Paulo Ricardo Motta Gomes <
>> wrote:
>> Hello,
>> I'm running repair on a large CF with the "--local" flag in 2 different
>> DCs. In one of the DCs the operation takes about 1 hour per node, while in
>> the other it takes 10 hours per node.
>> I would expect the times to differ, but not so much. The writes on that
>> CF all come from the DC where it takes 10 hours per node, could this be the
>> cause why it takes so long on this DC?
>> Additional info: C* 1.2.16, both DCs have the same replication factor.
>> Cheers,
>> --
>> *Paulo Motta*
>> Chaordic | *Platform*
>> * <>*
>> +55 48 3232.3200

*Paulo Motta*

Chaordic | *Platform*
* <>*
+55 48 3232.3200

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