Most efficient way to determine if 1000 specific keys exist?

Les Mikesell lesmikesell at
Sat May 5 18:09:38 EDT 2012

On Wed, May 2, 2012 at 1:47 PM, Tim Haines <tmhaines at> wrote:
> Hey guys,
> Still a relative newbie here.
> I was hoping to be able to setup a MapReduce job that I could feed 1000 keys
> to, and have it tell me of the 1000, which keys exist in the bucket.  I was
> hoping this could use the key index (such a thing exists right?) without
> having to read the objects.

I can't help with the question but I have some that are related...
Assuming you store things with discrete keys that can be computed,
like a prefix and a per-second timestamp, is there a rule of thumb
about how big a range would be more efficient to retrieve by asking
for all possible keys vs. a map-reduce?   Or is there a way to write a
map-reduce so that it computes the possible keys in a range and
returns any matching values instead of scanning the keyspace for them?

   Les Mikesell
     lesmikesell at

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