Archive for the ‘MapReduce’ Category

By Tasso Argyros in Blogroll, MapReduce on September 10, 2008

I am very excited about the power that In-Database MapReduce puts in the hands of the larger BI community. I’ll be leading a Night School session on In-Database MapReduce at the TDWI World Conference in November in New Orleans.

Please join me if you are interested in learning more about the MapReduce framework and its applications. I will introduce MapReduce from the basic principles, and then help build up your intuition. If we have time, I will even address why MapReduce is not UDF re-discovered. :-)

If you are unable to attend, or eager to understand, here are some MapReduce resources you may find informative: Aster’s whitepaper on In-Database MapReduce; Google Labs’ MapReduce research paper; Curt Monash’s post on Known Applications of MapReduce.

A great open-source project that I’d like to commend and draw your attention to illustrate the power of MapReduce is Apache’s Mahout Project, which is building machine learning algorithms on the MapReduce framework (Classification, Clustering, Regression, Dimension reduction and Evolutionary Algorithms).

I am sure this is just a snippet of the MapReduce resources available. If you have some that you have found helpful, please share them in your comments. I will be happy to review and cover them in our TDWI Night School!

By Tasso Argyros in Blogroll, Database, MapReduce on September 6, 2008

In response to Aster’s In-Database MapReduce initiative, I’ve been asked the following question:

“How does Aster Data Systems compete with open source MapReduce implementations, such as Hadoop?�

My answer – we simply do not.

Hadoop and Google’s implementation of MapReduce are targeted to the development (coding) community. The primary interface of these systems is the command line; and the primary means of accessing data is through Java or Python code. There have been efforts to build higher-level interfaces on top of these systems, but they are usually limited, do not follow any existing standard, and are incompatible with the existing filesystem.

Such tools are ideal for environments that are dominated by engineers, such as academic institutions, research labs or technology companies like Google/Yahoo that have a strong culture of in-house development (often hundreds of thousands of lines of code) to solve technical problems.

Most enterprises are unlike the culture of Google/Yahoo and each “build vs. buy” decision is carefully considered. Good engineering talent is a precious resource that is directed towards adding business value, not in building infrastructure from the ground up. The Data Services groups are universally under-staffed and consist of people that understand and leverage databases. As such, there are corporate governance expectations from any data management tool that they use:

- it has to comply with applicable standards like ANSI-SQL,

- it needs to provide a set of tools that IT can use & manage, and

- it needs to be ecosystem-friendly (BI and data integration tools compatibility).

In such an environment, using Java or developer-centric command line as the primary interface will increase the burden on the data services group and their IT counter-parts.

I strongly believe, that while existing MapReduce tools are good for development organizations, they are totally inappropriate for a large majority of enterprise IT departments.

Our goal is not to build yet another tool for development groups, but rather to create a product that unleashes the power of MapReduce for the enterprise IT organization.

How can we achieve that?

First, we’ve developed Aster to be a super-fast, always-parallel database for large-scale data warehousing using SQL. Then we allow our customers and partners to extend SQL through a tightly integrated MapReduce functionality.

The person that develops our MapReduce functions, naturally, needs to be a developer; but the person that is using this functionality can be an analyst using a standard BI tool (e.g., Microstrategy, Business Objects, Pentaho) over ODBC or JDBC connections!

Invoking MapReduce functions in Aster looks almost identical to writing standard SQL code. This way, the powerful MapReduce extensions that are developed by a small set of developers (either within an IT organization or by Aster itself) can be used by people with SQL skills using their existing sets of tools.

Integrating MapReduce and SQL is not an easy job; we had to innovate on multiple levels to achieve that, e.g. by creating a new type of UDFs that are both parallel and polymorphic, to make MapReduce extensions almost indistinguishable from standard SQL.

In summary, we have enabled:

- The flexible, parallel power of MapReduce to enable deep analytical insights that are impossible to express in standard SQL

- Seamless integration with ANSI standard SQL and all the rich commands, types, functions, etc. that are inherent in this well-known language

- Full JDBC/ODBC support ensures interoperability between Aster In-Database MapReduce and 3rd party database ecosystem tools like BI, reporting, advanced analytics (e.g., data mining), ETL, monitoring, scheduling, GUI administration, etc.

- SQL/MR functions – powerful plug-in operators that any non-engineer can easily plug into standard ANSI SQL to exploit the power of MapReduce analytic applications

- Polymorphism – unlike static, unreliable UDFs, SQL/MR functions unleash the power of polymorphism (run-time/dynamic) for cost-efficient reusability.  Built-in sandboxing ensures fault tolerance to avoid system crashes commonly experienced with UDFs

To conclude, it is important to understand that Aster nCluster is not yet another MapReduce implementation nor does it compete with Hadoop for resources or audience.

Rather, Aster nCluster is the world’s most powerful database that breaks traditional SQL barriers allowing Data Services groups and IT organizations to extract more knowledge out of their data

How Aster In-Database MapReduce Takes UDF’s to the Next Level
By Tasso Argyros in Blogroll, Database, MapReduce on August 27, 2008

Building on Mayank’s post, let me dig deeper into a few of the most important differences between Aster’s In-Database MapReduce and User Defined Functions (UDFs):

Feature User Defined Functions Aster SQL/MR Functions What does it mean?
———— ———— ———— ————
Dynamic Polymorphism No. Requires changing the code of the function and static declarations Yes SQL/MR functions work just like SQL extensions - no need to change function code
———— ———— ———— ————
Parallelism Only in some cases and for few number of nodes Yes, across 100s of nodes Huge performance increases even for the most complex functions
———— ———— ———— ————
Availability Ensured No. In most cases UDFs run inside the database Always. Functions run outside the database Even if functions have bugs, the system remains resilient to failures
———— ———— ———— ————
Data Flow Control No. Requires changing the UDF code or writing complex SQL subselects Yes. “PARTITION BY” and “SEQUENCE BY” natively control the flow of data in and out of the SQL/MR functions Input/output of SQL/MR functions can be redistributed across the database cluster in different ways with no actual function code change

In this blog post we’ll focus on Polymorphism - what it is and why it’s so critically important for building real SQL extensions using MapReduce.

Polymorphism allows Aster SQL/MR functions to be coded once (by a person that understands a programming or scripting language) and then used many times through standard SQL by analysts. In this context, comparing Aster SQL/MR functions and UDFs is like comparing SQL with the C language. The former is flexible, declarative and dynamic, the latter requires customization and recompilation even for the slightest change in usage.

For instance, take a SQL/MR function that performs sessionization. Let us assume that we have a webclicks(userId int, timestampValue timestamp, URL varchar, referrerURL varchar); table that contains a record of clicks for each user on our website. The same function, with no additional declarations, can be used in all the following ways:

SELECT sessionId, userId, timestampValue
FROM Sessionize( 'timestamp', 60 ) ON webclicks;

SELECT  sessionId, userId, timestampValue
FROM Sessionize( 'timestamp', 60 ) ON
(SELECT userid, timestampValue FROM webclicks WHERE userid = 50 );

[Note how the number of input arguments changed (going from all columns of webclicks; to just two columns of webclicks) in the above clause but the same function can be used. This is not possible with a plain UDF without writing additional declarations and UDF code]

SELECT  sessionId, UID, TS
FROM Sessionize( 'ts', 60 ) ON
(SELECT userid as UID, timestampValue as TS FROM webclicks WHERE userid = 50 );

[Note how the names of the arguments changed but the Sessionize() function does the right thing]

In other words, Aster SQL/MR functions are real SQL extensions - once they’ve been implemented there is zero need to change their code or write additional declarations - there is perfect separation between implementation and usage. This is an extremely powerful concept since in many cases the people that implement UDFs (engineers) and the people that use them (analysts) have different skills. Requiring a lot of back-and-forth can simply kill the usefulness of UDFs - but not so with SQL/MR functions.

How can we do that? There’s no magic, just technology. Our SQL/MR functions are dynamically polymorphic. To do this, our SQL/MR implementation (the sessionize.o file) includes not only code but also logic to determine its output schema based on its input, which is invoked at every query. This means that there is no need for a static signature as is the case with UDFs!

In-Database MapReduce Flow

Polymorphism also makes it trivial to nest different functions arbitrarily. Consider a simple example with two functions, Sessionize() and FindBots(). FindBots() can filter the input from any users that seem to act as bots, e.g. users whom interactions are very frequent (who could click on 10 links per second? probably not a human). To use these two functions in combination, one would simply write:

SELECT  sessionId, UserId, ts, URL
FROM Sessionize( 'ts', 60 ) ON FindBots( 'userid', 'ts' ) ON webclicks;

Using UDFs instead of SQL/MR functions would mean that this statement would require multiple subselects and special UDF declarations to accommodate the different inputs that come out of the different stages of the query.

So what is it that we have created? SQL? Or MapReduce? It really doesn’t matter. We just combined the best of both worlds. And it’s unlike anything else the world has seen!

By Mayank Bawa in Analytics, Analytics tech, Blogroll, Database, MapReduce on August 26, 2008

Pardon the tongue-in-cheek analogy to Oldsmobile when describing user-defined functions (UDFs), but I want to draw out some distinctions between this new class of functions that In-Database MapReduce enables.

Not Your Granddaddy's Oldsmobile

While similar on the surface, in practice there are stark differences between Aster In-Database MapReduce and traditional UDF’s.

MapReduce is a framework that parallelizes procedural programs to offload traditional cluster programming. UDF’s are simple database functions and while there are some syntactic similarities, that’s where the similarity ends. Several major differences between In-Database MapReduce and traditional UDF’s include:

Performance: UDF’s have limited or no parallelization capabilities in traditional databases (even MPP ones).  Even where UDF’s are executed in parallel in an MPP database, they’re limited to accessing local node data, have byzantine memory management requirements, require multiple passes and costly materialization.  In constrast, In-Database MapReduce automatically executes SQL/MR functions in parallel across potentially hundreds or even thousands of server nodes in a cluster, all in a single-pass (pipelined) fashion.

Flexibility: UDF’s are not polymorphic. Some variation in input/output schema may be allowed by capabilities like function overloading or permissive data-type handling, but that tends to greatly increase the burden on the programmer to write compliant code.  In contrast, In-Database MapReduce MR/SQL functions are evaluated at run-time to offer dynamic type inference, an attribute of polymorphism that offers tremendous adaptive flexibility previously only found in mid-tier object oriented programming.

Manageability: UDF’s are generally not sandboxed in production deployments. Most UDF’s are executed in-process by the core database engine, which means bad UDF code can crash a database. SQL/MR functions execute in their own process for full fault isolation (bad SQL/MR code results in an aborted query, leaving other jobs uncompromised). A strong process management framework also ensures proper resource management for consistent performance and progress visibility.

By Mayank Bawa in Analytics, Blogroll, Business analytics, MapReduce on August 25, 2008

I’m unbelievably excited about our new In-Database MapReduce feature!

Google has used MapReduce and GFS on page rank analysis, but the sky is really the limit for anyone to build powerful analytic apps. Curt Monash has posted an excellent compendium of applications that are successfully leveraging the MapReduce paradigm today.

A few examples of SQL/MapReduce functions that we’ve collaborated with our customers on so far:

1. Path Sequencing: SQL/MR functions can be used for developing regular expression matching of complex path sequences (eg. time series financial analysis or clickstream behavioral recommendations). It can also be extended to discover Golden Paths to reveal interesting behavioural patterns useful for segmentation, issue resolution, and risk optimization.

2. Graph Analysis: many interesting graph problems like BFS (breadth first search), SSSP (single source shortest path), APSP (all-pairs shortest path), and page rank that depend on graph traversal.

3. Machine Learning: several statistical algorithms like linear regression, clustering, collaborative filtering, naive bayes, support vector machine, and neural networks can be used to solve hard problems like pattern recognition, recommendations/market basket analysis, and classification/segmentation.

4. Data Transformations and Preparation: Large-scale transformations can be parameterized as SQL/MR functions for data cleansing and standardization, unleashing the true potential for Extract-Load-Transform pipelines and making large-scale data model normalization feasible. Push down also enables rapid discovery and data pre-processing to create analytical data sets used for advanced analytics such as SAS and SPSS.

These are just a few simple examples Aster has developed for our customers and partners via Aster’s In-Database MapReduce to help them with rich analysis and transformations of large data.

I’d like to finish with a simple code snippet example of a simple, yet powerful SQL/MR function we’ve developed called “Sessionization”

Our Internet customers have conveyed that defining a user session can’t be easily done (if at all) using standard SQL. One possibility is to use cookies but users frequently remove them or they expire.

Aster In-Database MapReduce

Aster developed a simple “Sessionization”Â? SQL/MR function via our standard Java API library to easily parameterize the discovery of a user session. A session would be defined by a timeout value (eg. in seconds). If the elapsed time between consecutive click events is greater than the timeout, this would signal a new session has begun for that user.

From a user perspective, the input is user clicks (eg. timestamp, userid). The output is to associate each click to a unique session identifier based on the Java procedure noted above. Here’s the simple syntax:

SELECT timestamp, userid, sessionid
FROM sessionize("timestamp", 600) ON clickstream
SEQUENCE BY timestamp

Indeed, it is that simple.

So simple, that we have reduced a complex multi-hour Extract-Load-Transform task into a toy example. That is the power of In-Database MapReduce!

By Mayank Bawa in Blogroll, Database, MapReduce on August 25, 2008

I am very pleased to announce today that Aster nCluster now brings together the expressive power of a MapReduce framework with the strengths of a Relational Database!

Jeff Dean and Sanjay Ghemawat at Google had invented the MapReduce framework in 2004 for processing large volumes of unstructured data on clusters of commodity nodes. Jeff and Sanjay’s goal was to provide a trivially parallelizable framework so that even novice developers (a.k.a interns) could write programs in a variety of languages (Java/C/C++/Perl/Python) to analyze data independent of scale. And, they have certainly succeeded.

Once implemented, the same MapReduce framework has been used successfully within Google (and outside, via Yahoo! sponsored Apache’s Hadoop) to analyze structured data as well.

In mapping our product trajectory, we realized early on that the intersection of MapReduce and Relational Databases for structured data analysis has a powerful consonance. Let me explain.

Relational Databases present SQL as an interface to manipulate data using a declarative interface rooted in Relational Algebra. Users can express their intent via set manipulations and the database runs off to magically optimize and efficiently execute the SQL request.

Such an abstraction is sunny and bright in the academic world of databases. However, any real-world practitioner of databases knows the limits of SQL and those of its Relational Database implementations: (a) a lack of expressive power in SQL (consider doing a Sessionization query in SQL!), and (b) a cost-based optimizer that often has a mind of its own refusing to perform the right operations.

Making an elephant dance!A final limitation of SQL is completely non-technical: most developers struggle with the nuances of making a database dance well to their directions. Indeed, a SQL maestro is required to perform interesting queries for data transformations (during ETL processing or Extract-Load-Transform processing) or data mining (during analytics).

These problems become worse at scale, where even minor weaknesses result in longer run-times. Most developers (the collective us), on the other hand, are much more familiar with programming in Java/C/C++/Perl/Python than in SQL.

MapReduce presents a simple interface for manipulating data: a map and a reduce function written in the language of choice (Java/C/C++/Perl/Python) of a developer. Its real power lies in the Expressivity it brings: it makes the phrasing of really interesting transformations and analytics breathtakingly easy. The fact that MapReduce, in its use of Map and Reduce functions is a “specific implementation of well known techniques developed nearly 25 years ago” is its beauty: every programmer understands it and knows how to leverage it.

As a computer scientist, I am thrilled at the simple elegant interface that we’ve enabled with SQL/MR. If our early beta trials with customers are any indication, databases have just taken a major step forward!

You can program a database too!You can now write against the database in a language of your choice and invoke these functions from within SQL to answer critical business questions. Data analysts will feel liberated to have simple powerful tools to compete effectively on analytics. More importantly, analysts now have simplicity, working within the environs of simple SQL that we all love.

The Aster nCluster will orchestrate resources transparently to ensure that tasks make progress and do not interfere with other concurrent queries and loads in the database.

Aster: Do More!We proudly present our SQL/MapReduce framework in Aster nCluster as the most powerful analytical database. Seamlessly integrating MapReduce with ANSI SQL provides a quantum leap that will empower analysts and ultimately unleash the power of data for the masses.

That is our prediction. And we are working to make it happen!