Hey Marcelo, You should check out spark. It intelligently deals with a lot of the issues you're mentioning. Al Tobey did a walkthrough of how to set up the OSS side of things here: http://tobert.github.io/post/2014-07-15-installing-cassandra-spark-stack.html
It'll be less work than writing a M/R framework from scratch :) Jon On Mon, Jul 21, 2014 at 8:24 AM, Marcelo Elias Del Valle <marc...@s1mbi0se.com.br> wrote: > Hi, > > I have the need to executing a map/reduce job to identity data stored in > Cassandra before indexing this data to Elastic Search. > > I have already used ColumnFamilyInputFormat (before start using CQL) to > write hadoop jobs to do that, but I use to have a lot of troubles to perform > tunning, as hadoop depends on how map tasks are split in order to > successfull execute things in parallel, for IO/bound processes. > > First question is: Am I the only one having problems with that? Is anyone > else using hadoop jobs that reads from Cassandra in production? > > Second question is about the alternatives. I saw new version spark will have > Cassandra support, but using CqlPagingInputFormat, from hadoop. I tried to > use HIVE with Cassandra community, but it seems it only works with Cassandra > Enterprise and doesn't do more than FB presto (http://prestodb.io/), which > we have been using reading from Cassandra and so far it has been great for > SQL-like queries. For custom map reduce jobs, however, it is not enough. > > Does anyone know some other tool that performs MR on Cassandra? My > impression is most tools were created to work on top of HDFS and reading > from a nosql db is some kind of "workaround". > > Third question is about how these tools work. Most of them writtes mapped > data on a intermediate storage, then data is shuffled and sorted, then it is > reduced. Even when using CqlPagingInputFormat, if you are using hadoop it > will write files to HDFS after the mapping phase, shuffle and sort this > data, and then reduce it. > > I wonder if a tool supporting Cassandra out of the box wouldn't be smarter. > Is it faster to write all your data to a file and then sorting it, or batch > inserting data and already indexing it, as it happens when you store data in > a Cassandra CF? I didn't do the calculations to check the complexity of each > one, what should consider no index in Cassandra would be really large, as > the maximum index size will always depend on the maximum capacity of a > single host, but my guess is that a map / reduce tool written specifically > to Cassandra, from the beggining, could perform much better than a tool > written to HDFS and adapted. I hear people saying Map/Reduce on > Cassandra/HBase is usually 30% slower than M/R in HDFS. Does it really make > sense? Should we expect a result like this? > > Final question: Do you think writting a new M/R tool like described would be > reinventing the wheel? Or it makes sense? > > Thanks in advance. Any opinions about this subject will be very appreciated. > > Best regards, > Marcelo Valle. -- Jon Haddad http://www.rustyrazorblade.com skype: rustyrazorblade
