Microsoft Cloud Authors: Yeshim Deniz, Janakiram MSV, John Katrick, David H Deans, Andreas Grabner

Related Topics: Microsoft Cloud, Machine Learning

Microsoft Cloud: Article

Garbage Collection in IE7

GC in IE7 is heavily impacted by number of JavaScript objects and string sizes

After my recent presentation at TSSJS – Performance Anti-Patterns in AJAX Applications - I got interesting feedback from one of the attendees: “The presentation was good but I thought you are talking more about actual problems with XHR/AJAX Requests”. I have to admit that I focused on all common problems of Web 2.0 applications – including network roundtrips, JavaScript and Rendering – and not just on those related to asynchronous communication. The comment made me work on a sample application where I want to test different approaches of asynchronous data processing that I’ve seen when working with our user base. I ran into a very interesting performance problem that I didn’t anticipate. So – before I write about the actual different approaches (XML vs. JSON, XHR vs. script tags, …) I want to share a performance problem in IE 7’s JavaScript engine that everybody should be aware of.

The more “active” JavaScript objects the slower your string manipulations

In my sample I process 1000 contact objects from two different data sources: XML and JSON. In case of XML I read element by element – create a JavaScript object and pass it to a method that appends the object’s content to a string buffer which will later be displayed on the page. In the JSON case I load all 1000 objects at once into an array and then hand each object to the same method by simply iterating over the array elements. Here is the pseudo code for my XML use case:

foreach(xmlElement in allXmlElements) {
var jsonObject = {};
jsonObject["firstName"] = xmlElement.getValueOf("firstName");
jsonObject["lastName"] = xmlElement.getValueOf("lastName");

And the pseudo code for JSON:

var allJsonObjects = eval(jsonObjectsAsString);
foreach(jsonObject in allJsonObjects) {

processObject itself is simply concatenating the individual properties of the JSON Object to a global string variable:

globalString += jsonObject.firstName + " " + jsonObject.lastName + ...

Running this example on Internet Explorer 7 is SLOW

I assumed that the 2nd use case (JSON) is much faster than the first as I assumed that iterating through the XML DOM is slower then parsing a string of JSON. Well, this assumption was correct (parsing through the XML is slower than parsing JSON), but the string concatenation in processObject turned out to be much slower in the JSON use case as compared to the XML use case.
Analyzing the JavaScript execution with the FREE dynaTrace AJAX Edition shows me all the 1000 invocations of processObject in both use case scenarios. In both cases execution time of the method increases over time – that is explained by a growing globalString object which gets more expensive to manipulate the larger the string grows. By the way, I know there are better ways to concatenate strings, and I should try out some of these recommendations. An excellent read here are the blogs from the guys at SitePen, e.g.: String Performance: An Analysis or String Performance: Getting Good Performance from Internet Explorer.

Let’s look at my results side-by-side showing the average execution time of processObject as well as the first couple of calls and the last couple of calls of the overall 1000 invocations of that method:

Execution Time Comparison between my two scenarios

Execution Time Comparison between my two scenarios

The left execution trace shows the JSON example where I constantly have 1000 JavaScript objects in memory (300ms). The right shows the XML example where I only have 1 JavsScript object in memory (150ms). The processObject method is called 1000 times in both scenarios and is doing exactly the same thing – concatenating the individual properties of the passed JavaScript object to a global string. The difference in execution time of these string concatenations, however, changes dramatically the longer the string gets. The only explanation I have for this “phenomenon” is that IE’s Memory Management is impacted greatly by having the additional 1000 JavaScript objects in memory (see my detailed analysis below the next image).

I copied the 1000 execution times of processObject for both use cases into an excel spreadsheet and graphed the timings. It’s interesting to see how the exec times change over time with an interesting spike at about 800 times the method was invoked:

JavaScript execution time over time

JavaScript execution time over time

The blue line shows the execution time of the scenario where I have the 1000 additional JavaScript objects in memory. The pink line shows the times with only 1 custom JavaScript object in memory. There are two interesting observations here – and I hope some of you (my fellow readers) can share your thoughts on it and correct me if my conclusions are incorrect: We see an increased exec time at the very beginning and a jump in execution time after about 800 executions of this method. I assume it has to do purely with the Garbage Collection and Object Allocation strategy of IE. Daniel Pupius’ blog about Garbage Collection in IE6 gives some answers on when IE kicks of the GC (after 256 variable allocations, 4096 array slot allocations and 64kb of String allocations). I am sure Microsoft has changed the GC strategy for IE7 but Daniel’s blog definitely explains the spike in my graph. My string size ends up being 79k. After about 800 executions it crosses the 64kb limit. Interesting is that from that point on I have constantly high execution times. So – the GC always runs when you have strings larger than 64kb!! I explain the individual smaller spikes with the GC runs triggered by 256 variable allocations. What I can’t explain is the much higher execution times in the very beginning – any thoughts?

Key takeaway: Be careful with string allocations and objects in memory -> GC in IE7 performs really badly

Running this example on IE8, FireFox and Chrome is FAST

I ran the same example on Internet Explorer 8, FireFox 3.6 and the latest version of Chrome. Not surprisingly the execution time on all of these latest versions of these browsers where between 2 and 15ms. These timings were the same for both use case scenarios (1 and 1000 objects in memory). Chrome and FireFox were in fact the fastest with only 2ms of execution time. IE8 took 15ms. The following graph shows the comparison between the tested browsers:

String Concatenation Times across Browsers

String Concatenation Times across Browsers


First of all – here is the actual sample I used. Click on the 1000 Objects and 1000 Objects (wArray). Test it on your machine and let me know if you experience any different behavior. I am also very happy to accept any recommendations on how to speed up this sample – I am sure there are many ways of doing so.

Second – it is important to understand the browsers internal memory management and the GC strategies. IE 7 will be here for a long long time so be careful with your object allocations. It also shows how important it is to test and analyze performance across browsers – especially on Internet Explorer. Most developers that I meet don’t use IE at all and purely focus on FF, Chrome or Safari. This often leads to the fact that problems like this here won’t show up until late in the project (when testers are testing the software across browsers and platforms) or when the page hits “The Real User” who happens to use IE quite a lot.

Third and final conclusion – I hope this was helpful. As always – if you are interested in more information check out some of the other AJAX Related blogs and watch some of the webinars we recorded with our clients, e.g.: the one I did with Monster.com.

Related reading:

  1. .NET Performance Analysis: A .NET Garbage Collection Mystery Memory Management in .NET is a broad topic with a...
  2. Week 8 – Challenges in Tracing JavaScript Performance by Example In an earlier post I already discussed several approaches towards...
  3. Performance Analysis of dynamic JavaScript Menus In my previous post I talked about the impact of...
  4. Performance Analysis: How to identify “bad” methods messing up the GC Whenever the Garbage Collector kicks in to free up memory...

More Stories By Andreas Grabner

Andreas Grabner has been helping companies improve their application performance for 15+ years. He is a regular contributor within Web Performance and DevOps communities and a prolific speaker at user groups and conferences around the world. Reach him at @grabnerandi

@ThingsExpo Stories
DX World EXPO, LLC, a Lighthouse Point, Florida-based startup trade show producer and the creator of "DXWorldEXPO® - Digital Transformation Conference & Expo" has announced its executive management team. The team is headed by Levent Selamoglu, who has been named CEO. "Now is the time for a truly global DX event, to bring together the leading minds from the technology world in a conversation about Digital Transformation," he said in making the announcement.
"Space Monkey by Vivent Smart Home is a product that is a distributed cloud-based edge storage network. Vivent Smart Home, our parent company, is a smart home provider that places a lot of hard drives across homes in North America," explained JT Olds, Director of Engineering, and Brandon Crowfeather, Product Manager, at Vivint Smart Home, in this SYS-CON.tv interview at @ThingsExpo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Events announced today that Conference Guru has been named “Media Sponsor” of the 22nd International Cloud Expo, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. A valuable conference experience generates new contacts, sales leads, potential strategic partners and potential investors; helps gather competitive intelligence and even provides inspiration for new products and services. Conference Guru works with conference organizers to pass great deals to gre...
The Internet of Things will challenge the status quo of how IT and development organizations operate. Or will it? Certainly the fog layer of IoT requires special insights about data ontology, security and transactional integrity. But the developmental challenges are the same: People, Process and Platform. In his session at @ThingsExpo, Craig Sproule, CEO of Metavine, demonstrated how to move beyond today's coding paradigm and shared the must-have mindsets for removing complexity from the develop...
In his Opening Keynote at 21st Cloud Expo, John Considine, General Manager of IBM Cloud Infrastructure, led attendees through the exciting evolution of the cloud. He looked at this major disruption from the perspective of technology, business models, and what this means for enterprises of all sizes. John Considine is General Manager of Cloud Infrastructure Services at IBM. In that role he is responsible for leading IBM’s public cloud infrastructure including strategy, development, and offering m...
"Evatronix provides design services to companies that need to integrate the IoT technology in their products but they don't necessarily have the expertise, knowledge and design team to do so," explained Adam Morawiec, VP of Business Development at Evatronix, in this SYS-CON.tv interview at @ThingsExpo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
To get the most out of their data, successful companies are not focusing on queries and data lakes, they are actively integrating analytics into their operations with a data-first application development approach. Real-time adjustments to improve revenues, reduce costs, or mitigate risk rely on applications that minimize latency on a variety of data sources. In his session at @BigDataExpo, Jack Norris, Senior Vice President, Data and Applications at MapR Technologies, reviewed best practices to ...
Widespread fragmentation is stalling the growth of the IIoT and making it difficult for partners to work together. The number of software platforms, apps, hardware and connectivity standards is creating paralysis among businesses that are afraid of being locked into a solution. EdgeX Foundry is unifying the community around a common IoT edge framework and an ecosystem of interoperable components.
Large industrial manufacturing organizations are adopting the agile principles of cloud software companies. The industrial manufacturing development process has not scaled over time. Now that design CAD teams are geographically distributed, centralizing their work is key. With large multi-gigabyte projects, outdated tools have stifled industrial team agility, time-to-market milestones, and impacted P&L stakeholders.
"Akvelon is a software development company and we also provide consultancy services to folks who are looking to scale or accelerate their engineering roadmaps," explained Jeremiah Mothersell, Marketing Manager at Akvelon, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
"IBM is really all in on blockchain. We take a look at sort of the history of blockchain ledger technologies. It started out with bitcoin, Ethereum, and IBM evaluated these particular blockchain technologies and found they were anonymous and permissionless and that many companies were looking for permissioned blockchain," stated René Bostic, Technical VP of the IBM Cloud Unit in North America, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Conventi...
In his session at 21st Cloud Expo, Carl J. Levine, Senior Technical Evangelist for NS1, will objectively discuss how DNS is used to solve Digital Transformation challenges in large SaaS applications, CDNs, AdTech platforms, and other demanding use cases. Carl J. Levine is the Senior Technical Evangelist for NS1. A veteran of the Internet Infrastructure space, he has over a decade of experience with startups, networking protocols and Internet infrastructure, combined with the unique ability to it...
22nd International Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, and co-located with the 1st DXWorld Expo will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud ...
"Cloud Academy is an enterprise training platform for the cloud, specifically public clouds. We offer guided learning experiences on AWS, Azure, Google Cloud and all the surrounding methodologies and technologies that you need to know and your teams need to know in order to leverage the full benefits of the cloud," explained Alex Brower, VP of Marketing at Cloud Academy, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clar...
Gemini is Yahoo’s native and search advertising platform. To ensure the quality of a complex distributed system that spans multiple products and components and across various desktop websites and mobile app and web experiences – both Yahoo owned and operated and third-party syndication (supply), with complex interaction with more than a billion users and numerous advertisers globally (demand) – it becomes imperative to automate a set of end-to-end tests 24x7 to detect bugs and regression. In th...
"MobiDev is a software development company and we do complex, custom software development for everybody from entrepreneurs to large enterprises," explained Alan Winters, U.S. Head of Business Development at MobiDev, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
Coca-Cola’s Google powered digital signage system lays the groundwork for a more valuable connection between Coke and its customers. Digital signs pair software with high-resolution displays so that a message can be changed instantly based on what the operator wants to communicate or sell. In their Day 3 Keynote at 21st Cloud Expo, Greg Chambers, Global Group Director, Digital Innovation, Coca-Cola, and Vidya Nagarajan, a Senior Product Manager at Google, discussed how from store operations and ...
"There's plenty of bandwidth out there but it's never in the right place. So what Cedexis does is uses data to work out the best pathways to get data from the origin to the person who wants to get it," explained Simon Jones, Evangelist and Head of Marketing at Cedexis, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Events announced today that CrowdReviews.com has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5–7, 2018, at the Javits Center in New York City, NY. CrowdReviews.com is a transparent online platform for determining which products and services are the best based on the opinion of the crowd. The crowd consists of Internet users that have experienced products and services first-hand and have an interest in letting other potential buye...
SYS-CON Events announced today that Telecom Reseller has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. Telecom Reseller reports on Unified Communications, UCaaS, BPaaS for enterprise and SMBs. They report extensively on both customer premises based solutions such as IP-PBX as well as cloud based and hosted platforms.