Playing with / understanding Riak configurations

Vikram Lalit vikramlalit at gmail.com
Thu Jul 28 13:10:46 EDT 2016


Thanks Tom...

On Wed, Jul 27, 2016 at 6:27 PM, Tom Santero <tsantero at gmail.com> wrote:

> Vikram,
>
> I apologize, I initially just skimmed your question and thought you were
> asking something entirely different.
>
> While increasing your N value is safe, decreasing it on a bucket with
> pre-existing data, as you have, is not-recommended and the source of your
> inconsistent results.
>
> Tom
>
> On Wed, Jul 27, 2016 at 4:18 PM, Vikram Lalit <vikramlalit at gmail.com>
> wrote:
>
>> Thanks Tom... Yes I did read that but I couldn't deduce the outcome if n
>> is decreased. John talks about data loss, but am actually observing a
>> different result... perhaps am missing something!
>>
>>
>> On Wed, Jul 27, 2016 at 6:11 PM, Tom Santero <tsantero at gmail.com> wrote:
>>
>>> Vikram,
>>>
>>> John Daily wrote a fantastic blog series that places your question in
>>> context and then answers it.
>>>
>>>
>>> http://basho.com/posts/technical/understanding-riaks-configurable-behaviors-part-1/
>>>
>>> Tom
>>>
>>> On Wed, Jul 27, 2016 at 4:07 PM, Vikram Lalit <vikramlalit at gmail.com>
>>> wrote:
>>>
>>>> Hi - I have a Riak node with n_val=3, r=2, w=2 and have just one
>>>> key-object stored there-in. I'm trying to test various configurations to
>>>> better understand the system and have the following observations - some
>>>> dont seem to align with my understanding so far, so appreciate if someone
>>>> can throw some light please... Thanks!
>>>>
>>>> 1. n=3, r=2, w=2: Base state, 1 key-value pair.
>>>>
>>>> 2. Change to n=2, r=2, w=2: When I query from my client, I randomly see
>>>> 1 or 2 values being fetched. In fact, the number of keys fetched is 1 or 2,
>>>> randomly changing each time the client queries the db. Ideally, I would
>>>> have expected that if we reduce the n_val, there would be data loss from
>>>> one of the vnodes. And that for this scenario, I would still expect only 1
>>>> (remaining) key-value pair to be read from the remaining two vnodes that
>>>> has the data. Note that I dont intend to make such a change in production
>>>> as cognizant of the recommendation to never decrease the value of n, but
>>>> have done so only to test out the details.
>>>>
>>>> 3. Then change to n=2, r=1, w=1: I get the same alternating result as
>>>> above, i.e. 1 or 2 values being fetched.
>>>>
>>>> 4. Then change to n=1, r=1, w=1: I get 3 key-value pairs, all
>>>> identical, from the database. Again, are these all siblings?
>>>>
>>>> _______________________________________________
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>>>> riak-users at lists.basho.com
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>>>>
>>>>
>>>
>>
>
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