Analysis of implementations of and issues associated with the parallel programming framework MapReduce. Related subjects include:

June 23, 2013

Impala and Parquet

I visited Cloudera Friday for, among other things, a chat about Impala with Marcel Kornacker and colleagues. Highlights included:

Data gets into Parquet via batch jobs only — one reason it’s important that Impala run against multiple file formats — but background format conversion is another roadmap item. A single table can be split across multiple formats — e.g., the freshest data could be in HBase, with the rest is in Parquet.

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June 6, 2013

Dave DeWitt responds to Daniel Abadi

A few days ago I posted Daniel Abadi’s thoughts in a discussion of Hadapt, Microsoft PDW (Parallel Data Warehouse)/PolyBase, Pivotal/Greenplum Hawq, and other SQL-Hadoop combinations. This is Dave DeWitt’s response. Emphasis mine.

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June 2, 2013

SQL-Hadoop architectures compared

The genesis of this post is:

I love my life.

Per Daniel (emphasis mine): Read more

May 29, 2013

Syncsort extends Hadoop MapReduce

My client Syncsort:

*Perhaps we should question Syncsort’s previous claims of having strong multi-node parallelism already. :)

The essence of the Syncsort DMX-h ETL Edition story is:

More details can be found in a slide deck Syncsort graciously allowed me to post. Read more

March 11, 2013

Hadoop execution enhancements

Hadoop 2.0/YARN is the first big step in evolving Hadoop beyond a strict Map/Reduce paradigm, in that it at least allows for the possibility of non- or beyond-MapReduce processing engines. While YARN didn’t meet its target of general availability around year-end 2012, Arun Murthy of Hortonworks told me recently that:

Arun further told me about Tez, the next-generation Hadoop processing engine he’s working on, which he also discussed in a recent blog post:

With the emergence of Apache Hadoop YARN as the basis of next generation data-processing architectures, there is a strong need for an application which can execute a complex DAG [Directed Acyclic Graph] of tasks which can then be shared by Apache Pig, Apache Hive, Cascading and others.  The constrained DAG expressible in MapReduce (one set of maps followed by one set of reduces) often results in multiple MapReduce jobs which harm latency for short queries (overhead of launching multiple jobs) and throughput for large-scale queries (too much overhead for materializing intermediate job outputs to the filesystem). With Tez, we introduce a more expressive DAG of tasks, within a single application or job, that is better aligned with the required processing task – thus, for e.g., any given SQL query can be expressed as a single job using Tez.

This is similar to the approach of BDAS Spark:

Rather than being restricted to Maps and Reduces, Spark has more numerous primitive operations, including map, reduce, sample, join, and group-by. You can do these more or less in any order.

although Tez won’t match Spark’s richer list of primitive operations.

More specifically, there will be six primitive Tez operations:

A Map step would compound HDFS input, output sorting, and output shuffling; a Reduce step compounds — you guessed it! — input sorting, input shuffling, and HDFS output.

I can’t think of much in the way of algorithms that would be logically impossible in MapReduce yet possible in Tez. Rather, the main point of Tez seems to be performance, performance consistency, response-time consistency, and all that good stuff. Specific advantages that Arun and I talked about included:

December 13, 2012

Spark, Shark, and RDDs — technology notes

Spark and Shark are interesting alternatives to MapReduce and Hive. At a high level:

The key concept here seems to be the RDD. Any one RDD:

Otherwise, there’s a lot of flexibility; an RDD can be a set of tuples, a collection of XML documents, or whatever other reasonable kind of dataset you want. And I gather that:

Read more

December 13, 2012

Introduction to Spark, Shark, BDAS and AMPLab

UC Berkeley’s AMPLab is working on a software stack that:

The whole thing has $30 million in projected funding (half government, half industry) and a 6-year plan (which they’re 2 years into).

Specific projects of note in all that include:

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November 29, 2012

Notes on Microsoft SQL Server

I’ve been known to gripe that covering big companies such as Microsoft is hard. Still, Doug Leland of Microsoft’s SQL Server team checked in for phone calls in August and again today, and I think I got enough to be worth writing about, albeit at a survey level only,

Subjects I’ll mention include:

One topic I can’t yet comment about is MOLAP/ROLAP, which is a pity; if anybody can refute my claim that ROLAP trumps MOLAP, it’s either Microsoft or Oracle.

Microsoft’s slides mentioned Yahoo refining a 6 petabyte Hadoop cluster into a 24 terabyte SQL Server “cube”, which was surprising in light of Yahoo’s history as an Oracle reference.

Read more

November 19, 2012

Couchbase 2.0

My clients at Couchbase checked in.

The big changes in Couchbase 2.0 versus the previous (1.8.x) version are:

Couchbase 2.0 is upwards-compatible with prior versions of Couchbase (and hence with Memcached), but not with CouchDB.

Technology notes on Couchbase 2.0 include: Read more

November 19, 2012

Incremental MapReduce

My clients at Cloudant, Couchbase, and 10gen/MongoDB (Edit: See Alex Popescu’s comment below) all boast the feature incremental MapReduce. (And they’re not the only ones.) So I feel like making a quick post about it. For starters, I’ll quote myself about Cloudant:

The essence of Cloudant’s incremental MapReduce seems to be that data is selected only if it’s been updated since the last run. Obviously, this only works for MapReduce algorithms whose eventual output can be run on different subsets of the target data set, then aggregated in a simple way.

These implementations of incremental MapReduce are hacked together by teams vastly smaller than those working on Hadoop, and surely fall short of Hadoop in many areas such as performance, fault-tolerance, and language support. That’s a given. Still, if the jobs are short and simple, those deficiencies may be tolerable.

A StackOverflow thread about MongoDB’s version of incremental MapReduce highlights some of the implementation challenges.

But all practicality aside, let’s return to the point that incremental MapReduce only works for some kinds of MapReduce-based algorithms, and consider how much of a limitation that really is. Looking at the Map steps sheds a little light: Read more

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