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From Vikram Kone <vikramk...@gmail.com>
Subject Need advice about OLAP on Hadoop
Date Fri, 27 Feb 2015 05:19:27 GMT
I'm a newbie when it comes to Spark and Hadoop eco system in general. Our
team has been predominantly a Microsoft shop that uses MS stack for most of
their BI needs. So we are talking SQL server  for storing relational data
and SQL Server Analysis services for building MOLAP cubes for sub-second
query analysis.
Lately, we have been hitting degradation in our cube query response times
as our data sizes grew considerably the past year. We are talking fact
tables which are in 1o-100 billions of rows range and a few dimensions in
the 10-100's of millions of rows. We tried vertically scaling up our SSAS
server but queries are still taking few minutes. In light of this, I was
entrusted with task of figuring out an open source solution that would
scale to our current and future needs for data analysis.
I looked at a bunch of open source tools like Apache Drill, Druid, AtScale,
Spark, Storm, Kylin etc and settled on exploring Spark as the first step
given it's recent rise in popularity and growing eco-system around it.
Since we are also interested in doing deep data analysis like machine
learning and graph algorithms on top our data, spark seems to be a good
I would like to build out a POC for our MOLAP cubes using spark with
HDFS/Hive as the datasource and see how it scales for our queries/measures
in real time with real data.
Roughly, these are the requirements for our team
1. Should be able to create facts, dimensions and measures from our data
sets in an easier way.
2. Cubes should be query able from Excel and Tableau.
3. Easily scale out by adding new nodes when data grows
4. Very less maintenance and highly stable for production level workloads
5. Sub second query latencies for COUNT DISTINCT measures (since majority
of our expensive measures are of this type) . Are ok with Approx Distinct
counts for better perf.

So given these requirements, is Spark the right solution to replace our
on-premise MOLAP cubes? Or should we look at Apache Drill? or something
else like MongoDB or Cassandra etc?
Are there any tutorials or documentation on how to build cubes using Spark?
Is that even possible? or even necessary? As long as our users can
pivot/slice & dice the measures quickly from client tools by dragging
dropping dimensions into rows/columns w/o the need to join to fact table,
we are ok with however the data is laid out. Doesn't have to be a cube. It
can be a flat file in hdfs for all we care. I would love to chat with some
one who has successfully done this kind of migration from OLAP cubes to
Spark in their team or company .

This is it for now. Looking forward to a great discussion.

P.S. We have decided on using Azure HDInsight as our managed hadoop system
in the cloud.

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