Simple mapreduce with 2i returns different result

Mattias Sjölinder mattias at sjolinder.se
Fri Apr 12 06:05:05 EDT 2013


Thanks for you response Christian!

We are having AAE enabled in our cluster. The thing that bothers me most is
that even if I get the expected dataset once in my MapReduce, a consecutive
identically request is often returning a subset of the result even if no
changes have been done to entire bucket. The same thing seems to happen for
all our MapReduce queries. The bucket in the example have both allow_mult
and last_write_wins set to false.

Regards
Mattias


2013/4/12 Christian Dahlqvist <christian at basho.com>

> Hi Mattias,
>
> MapReduce in Riak executes based on the data in a single partition and
> does, for efficiency reasons, not perform a quorum read (which greatly
> reduces the required amount of network traffic). As Riak is eventually
> consistent, it is possible that all partitions do not hold exactly the same
> data or version of the data at any point in time. What you are seeing could
> very well be a result of all replicas of some data not being in sync across
> all partitions holding a copy.
>
> This would however be corrected either through read-repair or AAE (Active
> Anti-Entropy) if you have this enabled. If you were to perform a GET on a
> key that is missing, triggering read-repair, I would expect it to
> consistently show up in the results from that point on, at least until it
> is updated again.
>
> Best regards,
>
> Christian
>
>
>
> On 12 Apr 2013, at 08:13, Mattias Sjölinder <mattias at sjolinder.se> wrote:
>
> Hi
>
> I struggling to get a grip around MapReduce and why it is sometimes
> returning only a subset of what is expected. Is it the nodes processing the
> map phase that after a specific time returning the found matches so far? I
> would rather have it returning timeout instead of a subset of the actual
> match.
>
> An example is this simple MapReduce:
>
> {
>     "inputs":{
>         "bucket":"som-bucket",
>         "index":"userid_bin",
>         "key":"18481123123"
>     },
>     "query":[
>         {
>             "map":{
>                 "language":"javascript",
>                 "name":"Riak.mapValuesJson",
>                 "keep":true
>             }
>         }
>     ]
> }
>
>
> Any thoughts?
>
> Regards
> Mattias
>
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