Getting a value: get vs map

Jonathan Langevin jlangevin at loomlearning.com
Fri Jul 29 10:59:40 EDT 2011


And it's a bit ironic that having data spread over more servers results in
slower performance. Usually more servers = greater performance.
...black is white, up is down...
*

<http://www.loomlearning.com/>
Jonathan Langevin
Systems Administrator
Loom Inc.
Wilmington, NC: (910) 241-0433 - jlangevin at loomlearning.com -
www.loomlearning.com - Skype: intel352
*


On Fri, Jul 29, 2011 at 10:27 AM, Jeremiah Peschka <
jeremiah.peschka at gmail.com> wrote:

> I would have suspected that an MR job where you supply a Bucket, Key pair
> would be just as fast as a Get request. Shows what I know.
> ---
> Jeremiah Peschka
> Founder, Brent Ozar PLF, LLC
>
> On Jul 29, 2011, at 1:37 AM, Antonio Rohman Fernandez wrote:
>
> > MapReduce ( or a simply Map ) gets really slow when database has a
> significant amount of data ( or distributed over several servers ). Get
> instead is always faster as Riak doesn't have to search for the key ( you
> tell Riak exactly where to GET the data in your url )
> >
> > Rohman
> >
> > On Thu, 28 Jul 2011 23:43:06 +0400, mss at mawhrin.net wrote:
> >
> >> Hi,
> >>
> >> (I looked at various places for the information, however I could not
> >> find anything that would answer the question.  It's not completely ruled
> >> out that not all places were checked though :))
> >>
> >> I use PB erlang interface to access the database.  Given a bucket name
> >> and a key, the value can easily be extracted using:
> >>
> >>     {ok, Object} = riakc_pb_socket:get(Conn, Bucket, Key),
> >>     Value = riakc_obj:get_value(Object)
> >>
> >> Alternatively, a mapred (actually, just map) request could be issued:
> >>
> >>     {ok, [{_, Value}]} = riakc_pb_socket:mapred(Conn, [
> >>         {Bucket, Key}
> >>     ], [
> >>         {map, {modfun, riak_kv, map_object_value}, none, true}
> >>     ])
> >>
> >> I would expect that the result is the same while in the second case, the
> >> amount of data transferred to the client is smaller (which might be good
> >> for certain situations).
> >>
> >> So the [open] question is: are there any reasons for using the first
> >> approach over the second?
> >>
> >> --
> >> Misha
> >>
> > --
> >
> >               Antonio Rohman Fernandez
> > CEO, Founder & Lead Engineer
> > rohman at mahalostudio.com               Projects
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