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From Edward Capriolo <edlinuxg...@gmail.com>
Subject Re: Fill disks more than 50%
Date Thu, 24 Feb 2011 15:42:14 GMT
On Thu, Feb 24, 2011 at 4:08 AM, Thibaut Britz
<thibaut.britz@trendiction.com> wrote:
> Hi,
>
> How would you use rsync instead of repair in case of a node failure?
>
> Rsync all files from the data directories from the adjacant nodes
> (which are part of the quorum group) and then run a compactation which
> will? remove all the unneeded keys?
>
> Thanks,
> Thibaut
>
>
> On Thu, Feb 24, 2011 at 4:22 AM, Edward Capriolo <edlinuxguru@gmail.com> wrote:
>> On Wed, Feb 23, 2011 at 9:39 PM, Terje Marthinussen
>> <tmarthinussen@gmail.com> wrote:
>>> Hi,
>>> Given that you have have always increasing key values (timestamps) and never
>>> delete and hardly ever overwrite data.
>>> If you want to minimize work on rebalancing and statically assign (new)
>>> token ranges to new nodes as you add them so they always get the latest
>>> data....
>>> Lets say you add a new node each year to handle next years data.
>>> In a scenario like this, could you with 0.7 be able to safely fill disks
>>> significantly more than 50% and still manage things like repair/recovery of
>>> faulty nodes?
>>>
>>> Regards,
>>> Terje
>>
>> Since all your data for a day/month/year would sit on the same server.
>> Meaning all your servers with old data would be idle and your servers
>> with current data would be very busy. This is probably not a good way
>> to go.
>>
>> There is a ticket open for 0.8 for efficient node moves joins. It is
>> already a lot better in 0.7. Pretend you did not see this (you can
>> join nodes using rsync if you know some tricks) if you are really
>> afraid of joins, which you really should not be.
>>
>> As for the 50% statement. In a worse case scenario a major compaction
>> will require double the disk size of your column family. So if you
>> have more then 1 column family you do NOT need 50% overhead.
>>
>
@Thibaut Britz
Caveat:Using simple strategy.
This works because cassandra scans data at startup and then serves
what it finds. For a join for example you can rsync all the data from
the node below/to the right of where the new node is joining. Then
join without bootstrap then cleanup both nodes. (also you have to
shutdown the first node so you do not have a lost write scenario in
the time between rsync and new node startup)

It does not make as much sense for repair because the data on a node
will tripple, before you compact/cleanup it.

@Terje
I am suggesting that your probably want to rethink your scheme design
since partitioning by year is going to be bad performance since the
old servers are going to be nothing more then expensive tape drives.

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