Welcome!

Big Data Journal Authors: Yeshim Deniz, Greg Ness, Mat Mathews, Pat Romanski, Carmen Gonzalez

Related Topics: Java, Open Source, AJAX & REA, Web 2.0, Cloud Expo, Big Data Journal

Java: Article

How to Identify a MongoDB Performance Anti Pattern in Five Minutes

Analyzing the application

The other day I was looking at a web application that was using MongoDB as its central database. We were analyzing the application for potential performance problems and inside five minutes I detected what I must consider to be a MongoDB anti pattern and had a 40% impact on response time. The funny thing: It was a Java best practice that triggered it.

Analyzing the Application
The first thing I always do is look at the topology of an application to get a feel for it.

Overall Transaction Flow of the Application

As we see it's a modestly complex web application and it's using MongoDB as its datastore. Overall MongoDB contributes about 7% to the response time of the application. I noticed that about half of all transactions are actually calling MongoDB so I took a closer look.

Flow of Transactions that access MongoDB, showing 10% response time contribution of MongoDB

Those transactions that actually do call MongoDB spend about 10% of their response time in that popular document database. As a next step I wanted to know what was being executed against MongoDB.

Overview of all MongoDB commands. This shows that the JourneyCollection find and getCount contribute the most to response time

One immediately notices the first two lines, which contribute much more to the response time per transaction than all the others. What was interesting was that thegetCount on the JourneyCollection had the highest contribution time, but the developer responsible was not aware that he was even using it anywhere.

Things get interesting - the mysterious getCount call
Taking things one level deeper, we looked at all transactions that were executing the ominous getCount on the JourneyCollection.

Transactions that call JourneyCollection.getCount spend nearly half their time in MongoDB

What jumps out is that those particular transactions spend indeed over 40% of their time in MongoDB, so there was a big potential for improvement here. Another click and we looked at all MongoDB calls that were executed within the context of the same transaction as the getCount call we found so mysterious.

All MongoDB Statements that run within the same transaction context as the JourneyCollection.getCount

What struck us as interesting was that the number of executions per transaction of thefind and getCount on the JourneyCollection seemed closely connected. At this point we decided to look at the transactions themselves - we needed to understand why that particular MongoDB call was executed.

Single Transactions that execute the ominous getCount call

It's immediately clear that several different transaction types are executing that particulargetCount. What that meant for us is that the problem was likely in the core framework of that particular application rather than being specific to any one user action. Here is the interesting snippet:

The Transaction Trace shows where the getCount is executed exactly

We see that the WebService findJourneys spends all its time in the two MongoDB calls. The first is the actual find call to the Journey Collection. The MongoDB client is good at lazy loading, so the find does not actually do much yet. It only calls the server once we access the result set. We can see the round trip to MongoDB visualized in the call node at the end.

We also see the offending getCount. We see that it is executed by a method called sizewhich turns out to be com.mongodb.DBCursor.size method. This was news to our developer. Looking at several other transactions we found that this was a common pattern. Every time we search for something in the JourneyCollection the getCountwould be executed by com.mongodb.DBCursor.size. This always happens before we would really execute the send the find command to the server(which happens in the callmethod). So we used CompuwareAPM DTM's (a.k.a dynaTrace) developer integration and took a look at the offending code. Here is what we found:

BasicDBObject fields = new BasicDBObject();
fields.put(journeyStr + "." + MongoConstants.ID, 1);
fields.put(MongoConstants.ID, 0);

Collection locations = find(patternQuery, fields);

ArrayList results = new ArrayList(locations.size());
for (DBObject dbObject : locations) {
String loc = dbObject.getString(journeyStr);
results.add(loc);
}
return results;


The code looks harmless enough; we execute a find, create an array for the result and fill it. The offender is the location.size(). MongoDBs DBCursor is similar to the ResultSet in JDBC, it does not return the whole data set at once, but only a subset. As a consequence it doesn't really know how many elements the find will end up with. The only way for MongoDB to determine the final size seems to be to execute a getCountwith the same criteria as the original find. In our case that additional unnecessary roundtrip made up 40% of the web services response time!

An Anti-Patter triggered by a Best Practice
So it turns out that calling size on the DBCursor must be considered an anti-pattern! The real funny thing is that the developer thought he was writing performant code. He was following the best practice to pre-size arrays. This avoids any unnecessary re-sizing. In this particular case however, that minor theoretical performance improvement led to a 40% performance degradation!

Conclusion
The take away here is not that MongoDB is bad or doesn't perform. In fact the customer is rather happy with it. But mistakes happen and similar to other database applications we need to have the visibility into a running application to see how much it contributes to the overall response time. We also need to have that visibility to understand which statements are called where and why.

In addition this also demonstrates nicely why premature micro optimization, without leveraging an APM solution, in production will not lead to better performance. In some cases - like this one - it can actually lead to worse performance.

More Stories By Michael Kopp

Michael Kopp has over 12 years of experience as an architect and developer in the Enterprise Java space. Before coming to CompuwareAPM dynaTrace he was the Chief Architect at GoldenSource, a major player in the EDM space. In 2009 he joined dynaTrace as a technology strategist in the center of excellence. He specializes application performance management in large scale production environments with special focus on virtualized and cloud environments. His current focus is how to effectively leverage BigData Solutions and how these technologies impact and change the application landscape.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


@BigDataExpo Stories
The definition of IoT is not new, in fact it’s been around for over a decade. What has changed is the public's awareness that the technology we use on a daily basis has caught up on the vision of an always on, always connected world. If you look into the details of what comprises the IoT, you’ll see that it includes everything from cloud computing, Big Data analytics, “Things,” Web communication, applications, network, storage, etc. It is essentially including everything connected online from ha...
Cloud Expo 2014 TV commercials will feature @ThingsExpo, which was launched in June, 2014 at New York City's Javits Center as the largest 'Internet of Things' event in the world.
An entirely new security model is needed for the Internet of Things, or is it? Can we save some old and tested controls for this new and different environment? In his session at @ThingsExpo, New York's at the Javits Center, Davi Ottenheimer, EMC Senior Director of Trust, reviewed hands-on lessons with IoT devices and reveal a new risk balance you might not expect. Davi Ottenheimer, EMC Senior Director of Trust, has more than nineteen years' experience managing global security operations and asse...

ARMONK, N.Y., Nov. 20, 2014 /PRNewswire/ --  IBM (NYSE: IBM) today announced that it is bringing a greater level of control, security and flexibility to cloud-based application development and delivery with a single-tenant version of Bluemix, IBM's

The major cloud platforms defy a simple, side-by-side analysis. Each of the major IaaS public-cloud platforms offers their own unique strengths and functionality. Options for on-site private cloud are diverse as well, and must be designed and deployed while taking existing legacy architecture and infrastructure into account. Then the reality is that most enterprises are embarking on a hybrid cloud strategy and programs. In this Power Panel at 15th Cloud Expo (http://www.CloudComputingExpo.com...
Explosive growth in connected devices. Enormous amounts of data for collection and analysis. Critical use of data for split-second decision making and actionable information. All three are factors in making the Internet of Things a reality. Yet, any one factor would have an IT organization pondering its infrastructure strategy. How should your organization enhance its IT framework to enable an Internet of Things implementation? In his session at Internet of @ThingsExpo, James Kirkland, Chief Ar...
Technology is enabling a new approach to collecting and using data. This approach, commonly referred to as the "Internet of Things" (IoT), enables businesses to use real-time data from all sorts of things including machines, devices and sensors to make better decisions, improve customer service, and lower the risk in the creation of new revenue opportunities. In his General Session at Internet of @ThingsExpo, Dave Wagstaff, Vice President and Chief Architect at BSQUARE Corporation, discuss the ...
The security devil is always in the details of the attack: the ones you've endured, the ones you prepare yourself to fend off, and the ones that, you fear, will catch you completely unaware and defenseless. The Internet of Things (IoT) is nothing if not an endless proliferation of details. It's the vision of a world in which continuous Internet connectivity and addressability is embedded into a growing range of human artifacts, into the natural world, and even into our smartphones, appliances, a...
"BSQUARE is in the business of selling software solutions for smart connected devices. It's obvious that IoT has moved from being a technology to being a fundamental part of business, and in the last 18 months people have said let's figure out how to do it and let's put some focus on it, " explained Dave Wagstaff, VP & Chief Architect, at BSQUARE Corporation, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4-6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
The 4th International DevOps Summit, co-located with16th International Cloud Expo – being held June 9-11, 2015, at the Javits Center in New York City, NY – announces that its Call for Papers is now open. Born out of proven success in agile development, cloud computing, and process automation, DevOps is a macro trend you cannot afford to miss. From showcase success stories from early adopters and web-scale businesses, DevOps is expanding to organizations of all sizes, including the world's large...
The 3rd International @ThingsExpo, co-located with the 16th International Cloud Expo - to be held June 9-11, 2015, at the Javits Center in New York City, NY - announces that it is now accepting Keynote Proposals. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devices - computers, smartphones, tablets, and sensors - connected to th...
As cloud gives an opportunity to businesses to buy services externally – how is cloud impacting your customers? In his General Session at 15th Cloud Expo, Fabio Gori, Director of Worldwide Cloud Marketing at Cisco, provided answers to big questions: Do you see hybrid cloud as where the world is going? What benefits does it bring? And how does Cisco connect all of these clouds? He also discussed Intercloud and Cisco’s investment on it.
SYS-CON Events announced today that Windstream, a leading provider of advanced network and cloud communications, has been named “Silver Sponsor” of SYS-CON's 16th International Cloud Expo®, which will take place on June 9–11, 2015, at the Javits Center in New York, NY. Windstream (Nasdaq: WIN), a FORTUNE 500 and S&P 500 company, is a leading provider of advanced network communications, including cloud computing and managed services, to businesses nationwide. The company also offers broadband, p...
Working with Big Data is challenging, especially when decision makers depend on market insights and intelligence from your data but don't have quick access to it or find it unusable. In their session at 6th Big Data Expo, Ian Khan, Global Strategic Positioning & Brand Manager at Solgenia; Zel Bianco, President, CEO and Co-Founder of Interactive Edge of Solgenia; and Ermanno Bonifazi, CEO & Founder at Solgenia, discussed how a revolutionary cloud-based BI along with mobile analytics is already c...
There is no doubt that Big Data is here and getting bigger every day. Building a Big Data infrastructure today is no easy task. There are an enormous number of choices for database engines and technologies. To make things even more challenging, requirements are getting more sophisticated, and the standard paradigm of supporting historical analytics queries is often just one facet of what is needed. As Big Data growth continues, organizations are demanding real-time access to data, allowing immed...
Vichara Technologies in Hoboken, New Jersey is expanding its capabilities in big data from origins on Wall Street into other areas, and thereby demonstrating the growing marketplace for advanced big-data analytics services. The next BriefingsDirect deep-dive big data benefits case study interview explores how Vichara Technologies in Hoboken, New Jersey is expanding its capabilities in big data from origins on Wall Street into other areas, and thereby demonstrating the growing marketplace for ad...
Moscow-based OpenBank, one of the largest private financial services groups in Russia, has built out a business intelligence capability for wholly new business activity monitoring benefits. The next BriefingsDirect deep-dive big data benefits case study interview explores how Moscow-based Otkritie Bank, one of the largest private financial services groups in Russia, has built out a business intelligence (BI) capability for wholly new business activity monitoring (BAM) benefits. The use of HP V...
The 3rd International Internet of @ThingsExpo, co-located with the 16th International Cloud Expo - to be held June 9-11, 2015, at the Javits Center in New York City, NY - announces that its Call for Papers is now open. The Internet of Things (IoT) is the biggest idea since the creation of the Worldwide Web more than 20 years ago.
Scene scenario: 10 am in a boardroom somewhere, second round of coffees served, Danish and donuts untouched, a quiet hush settles. “Well you know what guys? (and, by the use of the term guys I mean to include both sexes here assembled) – the trouble that we have as a company is that we are, to put it bluntly, just a little analytics poor,” said the newly appointed Chief Analytics Officer. That we should consider a firm to be analytically deficient or poor is a profound comment on our modern ag...
Quantum is a leading expert in scale-out storage, archive and data protection, providing intelligent solutions for capturing, sharing and preserving digital assets over the entire data lifecyle. They help customers maximize the value of these assets to achieve their goals, whether it’s top movie studios looking to create the next blockbuster, researchers working to accelerate scientific discovery, or small businesses trying to streamline their operations. With a comprehensive portfolio of best-i...