Inconsistent map/reduce results

Antonio Rohman Fernandez rohman at mahalostudio.com
Thu Mar 10 21:56:53 EST 2011



if you want to avoid caching ( without configuration ), you can put
some random variable in your map or reduce or both... that does the
trick for me as the query will be always different: 

$seed =
randomStringHere;

{"map":{"language":"javascript","source":"function(v,k,a)
{ seed='.$seed.'; x=Riak.mapValuesJson(v)[0]; return
[v.values[0].data]; }"} 

Rohman 

On Thu, 10 Mar 2011 17:47:49 -0800,
Keith Dreibelbis  wrote:  

Thanks for the prompt response, Grant. I
made the configuration change you suggested, and it fixed my problem.


Some followup questions: 

- is it possible to configure this
dynamically on a per-bucket basis, or just per-server like it is now? 
-
is this fixed in a newer version?

On Thu, Mar 10, 2011 at 2:56 PM,
Grant Schofield  wrote:

There are currently some bugs in the mapreduce
caching system. The best thing to do would be to disable the feature, on
0.13 you can do this by editing or adding the vnode_cache_entries to the
riak_kv section of your app.config. The entry would look like:

{vnode_cache_entries, 0}, 

Grant Schofield 
Developer Advocate  
Basho
Technologies  

On Mar 10, 2011, at 4:16 PM, Keith Dreibelbis wrote:   


Hi riak-users, 

I'm trying to do a map/reduce query from java on a
0.13 server, and get inconsistent results. What I'm doing should be
pretty simple. I'm hoping someone will notice an obvious error in here,
or have some insight: 

This is an automated test. I'm doing a simple
query where I'm trying to get the keys for records with a certain field
value. In SQL it would look like "SELECT id FROM table WHERE age =
'32'". In java I'm invoking it like this: 

 MapReduceResponse r =
riak.mapReduceOverBucket(getBucket()) 

.map(JavascriptFunction.anon(func), true) 
 .submit();  

where riak is
a RiakClient, getBucket() returns the name of the bucket, and func is a
string that looks like: 

function(value, keyData, arg) { 
 var data =
Riak.mapValuesJson(value)[0]; 
 if(data.age == "32") 
 return
[value.key]; 
 else 
 return []; 
 }  

No reduce phase. All entries in
the example bucket are json and have an age field. This initially works
correctly, it gets back the matching records as expected. It also works
in curl. It's an automated test, so each time I run this, it is using a
different bucket. After about a dozen queries, this starts to fail. It
returns an empty result, when it should have found records. It fails in
curl at the same time. 

I initially suspected this might have something
to do with doing map reduce too soon after writing, and the write not
being available on all nodes. However, I changed the bucket schema
entries for w,r,rw,dw from "quorum" to "all", and this still happens (is
there another bucket setting I missed?). In addition, I only have 3
nodes (I'm using the dev123 example), and am running curl long enough
afterwards. 

Here's the strange part that makes me suspicious. If I
make insignificant changes to the query, for example change the double
quotes to single quotes, add whitespace or extra parentheses, etc, then
it suddenly works again. It will work on an existing bucket, and on
subsequent tests, but again only about a dozen times before it starts
failing again. Same behavior in curl. This makes me suspect that the
server is doing some incorrect caching around this js function, based on
the function string. 

Any explanation about what's going on? 

Keith  
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