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From Aji Janis <>
Subject Re: Mapreduce, Indexing and Logging
Date Sun, 03 Mar 2013 19:14:49 GMT
John and Ed thank you both for your responses.

Using Solr for search is a requirement. When we process data theres quite a
bit of information we are interested in indexing (dates, locations, etc)
and we use Solr for that. All the data will be stored in Accumulo after
processing and then indexed in solr. But since I am trying to do all the
processing in map reduce I was interested in hearing any limitations there
might be if N (>=60) mappers or reducers try to put things in solr after
processing and before writing to accumulo.

On Sun, Mar 3, 2013 at 12:32 PM, Ed Kohlwey <> wrote:

> With respect to indexing, what are you trying to achieve? I have not used
> Solr with Accumulo but have done indexing directly in Accumulo, leveraging
> Lucene libraries as appropriate. You can get very good performance specific
> to your domain by doing so and its less O&M overhead. Of c course then you
> need to learn all about indexing so there's a little bit of a tradeoff.
> On Mar 2, 2013 12:50 PM, "John Vines" <> wrote:
>> 1. This is quite variable. It depends on your hardware specs, primarily
>> CPU and disk throughput. It also depends on how your system is configured
>> for these resources and your typical mutation size. How your mutations are
>> distributed is another factor.
>> 2. Under the hood, the output format uses a BatchWriter. There is a
>> guarantee that once a flush comes back from the batchwriter, the data is
>> available. Unless explicitly called, the batchwriter will flush whenever
>> half of it's capacity is full, or when idle for a short period (I want to
>> say 3 seconds, but I could be mistaken).
>> 3. If the 2 mutations don't intersect at all, then there's no issue. If
>> they have identical columns, then whichever one has the newest timestamp
>> will come up first. If you are explicitly setting timestamps or they arrive
>> at the same time, the outcome is non-deterministic.
>> 4. I'm going to defer this question to someone else
>> 5. Ideally each datanode should be a tserver. And they will also be a
>> tasktracvker. This will help ensure data locality so you can get around any
>> network boundaries/overhead.
>> 5. I don't see why not. There's a little bit of log4j statements in the
>> Accumulo client, so it would actually make it easier for you to deal with
>> them there too.
>> John
>> On Sat, Mar 2, 2013 at 3:11 PM, Aji Janis <> wrote:
>>> Hello,
>>>  I am investigating how well accumulo will handle mapreduce jobs. I am
>>> interested in hearing about any known issues from anyone running mapreduce
>>> with accumulo as their source and sink. Specifically, I want to hear your
>>> thoughts about the following:
>>> Assume cluster has 50 nodes.
>>> Accumulo running is on three nodes
>>> Solr is on three nodes
>>> 1. how many concurrent mutations can accumulo handle - more details on
>>> how this works would be extremely helpful
>>> 2. is there a delay between when map reduce writes data to table vs.
>>> when the data is available for read.
>>> 3. how are concurrent mutations to the same row handled  (say from
>>> different mappers/reducers) since accumulo isn't transactional
>>> 4. I am trying to solr index some accumulo data --- are there are any
>>> know issues on accumulo end? solr end? how does one vs. multiple shard
>>> affect the MR job?
>>> 5. should I have more accumulo/ solr nodes (ie an instance on each node
>>> in cluster? is that necessary? workarounds?)
>>> 5. Normally I have log4j statements all over the java job. Can I still
>>> use them with map reduce?
>>> I apologize if any of these questions do not belong on this mailing list
>>> (and please point me to where I can ask them, if possible). I am trying to
>>> gather a lot of information to decide if this is a good approach for me and
>>> the level of effort needed so I realize these are a lot of questions. I
>>> very much appreciate any and all feedback. Thank you for your time in
>>> advance!

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