Java Authors: Elizabeth White, Trevor Parsons, Robert Reeves, Jnan Dash, Pat Romanski

Related Topics: SOA & WOA, Java, XML, .NET, AJAX & REA, Web 2.0

SOA & WOA: Article

Evaluating the Performance of SPDY-Enabled Web Servers

With all the advantages of SPDY, you may be wondering if there is a price to pay on the server side

As you may already know, SPDY (pronounced "SPeeDY") is a new networking protocol introduced by Google and designed to reduce the web latency associated with HTTP. With SPDY, web pages load up to 64 percent faster than HTTP alone, according to Google. It accomplishes this by adding a session layer between HTTP and SSL that supports concurrent, interleaved streams over a single TCP connection. The initial draft of HTTP/2.0, the future of the web, is based on SPDY, which is a welcome step forward considering that HTTP/1.0 was released in 1996. SPDY holds great potential for mobile devices, for which latency is more of an issue, and the market is catching on. As evidence of this, Microsoft recently announced the next version of Internet Explorer will support the new protocol.

Today, SPDY can be deployed on Apache by installing a single module (mod-spdy, the Apache SPDY module). No changes to website content are required. SPDY is now enabled by default on many of the latest modern browsers, including Chrome, Firefox, Opera, and Android Browser. (You can check your own browser's support by visiting isspdyenabled.com.)

Simply by deploying the SPDY module on your Apache server, you can provide a large percentage of your users with better response times. More important, the response times of a website are correlated with the site's conversion rate and bounce rate - so SPDY can have a significant positive impact on your business!

With all the advantages of SPDY, you may be wondering if there is a price to pay on the server side. Moving from HTTP to SPDY adds encryption and compression overhead, which clearly requires more resources. It does, however, use fewer TCP connections. It wasn't immediately clear to me if all these changes in aggregate would cause noticeable drawbacks on the server.

To get to the bottom of this question, I thought it would be interesting to get some real-world performance metrics on SPDY, in particular its effect on the server side. To obtain this information, I used the new SPDY support in NeoLoad to run load tests of SPDY and compare its performance against HTTP and HTTPS.

Test Configuration Details
My approach was to test a server with a fairly typical configuration - not one that is finely tuned for a specific purpose. This setup provides a basis for comparing HTTP, HTTPS and SPDY. It's important to note here that changes to the application or the server configuration will produce different results - perhaps vastly different.

Test setup:
●     Server:
○     OS: Linux CentOS 6.3
○     Hardware:
■      Intel Core i3 CPU 540 @ 3.07GHz
■     4GB RAM
○     Apache
■     Version 2.2.15
■     worker MPM:
>StartServers    5
MaxClients      600
MinSpareThreads       50
MaxSpareThreads      150
ThreadsPerChild         50
MaxRequestsPerChild 0

■     SPDY module (mod-spdy-beta- Default SPDY optimization flags were used (uncommented suggested values):
●     SpdyMaxThreadsPerProcess 30
●     SpdyMaxStreamsPerConnection 100
●     Application:
○     1 web page: 1 HTML 9.5kB + 50 PNG icons (32x32).
○     The web page and all resources were served by the same server.
●     Load testing tool: NeoLoad 4.1.2
●     Tests:
○     Ramp-up from 1 to 1000 users for 20 minutes.
○     Scenario: 1 page call, wait for 5s, restart.
○     Chrome browser simulated, with 6 parallel connections to the server.
○     Emulated latency: 40ms in download, 45ms in upload.
○     Test HTTP, HTTPS, and SPDY under the same conditions.
○      Aggregation period of 30s for graphs. This smoothes variations to simplify comparison between several tests.

Results and Analysis
First I wanted to examine the hit rate (hits per second), average response time (duration), and number of errors as the number of concurrent users increased.

Here are the results for the HTTP test:

The plot illustrates the following:

  • At three minutes, the maximum number of page per second is reached. This maximum rate (16 pages/s or 827 request/s) is reached at 120 virtual users (VU), and the rate decreases as more concurrent users are added.
  • At the same time (the three-minute mark), response time starts to increase significantly.
  • The first errors (which investigation revealed to be timeouts) appear at 405 users.

The table below compares these metrics for HTTP, HTTPS, and SPDY:





Maximum pages/s

16.3 pages/s

after 3 minutes at 120 users

15.9 pages/s

after 3 minutes at 120 users

98 pages/s

after 14 minutes at 777 users

Page response time at 100 users




Page response time at 120 users

1.4 s



Page response time at 200 users




Page response time at 777 users




First error

405 Users

225 Users

884 Users

Service-level agreement violation (< 3s page load time)

133 Users

133 Users

794 Users


Based on a service-level agreement (SLA) of less than 3s for page load time, my test server handled almost six times as many users with SPDY than HTTP.

More users with fewer workers
To handle incoming requests in parallel, Apache web servers use worker threads to process each request. Because each thread consumes resources and memory, Apache lets the system administrator limit thread use, which has an effect on how incoming requests are handled.

My HTTP and HTTPS results are typical of a scenario known as thread starvation.

This is confirmed by the following graph, which shows busy workers in orange, page rate in green, and user load in blue:

The number of busy Apache workers (threads) hits its maximum at the same time the page rate reaches its maximum.

In contrast to HTTP/S, SPDY uses a single connection for all requests. The principal benefit of this is the decreased latency seen by the client, resulting in reduced response times for users. There is another great benefit on the server side: SPDY clients consume one worker instead of six. As a result it takes much longer (that is, many more users) for all workers to become busy:

SPDY enables the server to handle more users with the same number of workers.

Server CPU and memory consumption
So far, I showed how SPDY affects Apache worker usage with my test configuration. Next, I wanted to see how CPU usage and memory were affected by SPDY.

Here is a plot showing system idle time (low when the CPU is used intensively) for HTTP/HTTPS/SPDY:

No surprise here - as most HTTP/HTTPS requests are waiting to be served after the thread limit is reached, they don't consume much CPU. For the SPDY tests, Apache is below the worker limit for much longer, resulting in a higher page rate and consequently more CPU used. The curve plateau is reached when all workers are busy (around 11 minutes).

To better understand the behavior before the worker limit is reached, I focused on the numbers at two minutes, 88 virtual users, and 12.5 pages/s. The CPU idle time measurements are an average of six values taken over 30 seconds:





CPU Idle time at 2 minutes




The values are comparable; SPDY consumes slightly less CPU than HTTPS and slightly more than HTTP for this load.

On the memory side, here's the global overview:

Again, it's interesting to examine the memory used before the worker limit is reached. The numbers are an average of six measurements over 30 seconds.

System Memory



Difference = Consumed Memory


3,357 MB

3,416 MB

59 MB


3,500 MB

3,579 MB

79 MB


3,607 MB

3,631 MB

24 MB

The server consumed less memory when handling SPDY requests than when handling HTTP and HTTPS.

During this test, SPDY consumed just 41% of the memory consumed by HTTP, and just 30% of the memory consumed by HTTPS.

It's no surprise that SPDY improves response times on the client side; that's what it was designed to do. It turns out that SPDY also has advantages on the server side:

  • Compared to HTTPS, SPDY requests consume fewer resources (CPU and memory) on the server.
  • Compared to HTTP, SPDY requests consume less memory but a bit more CPU. This may be good, bad, or irrelevant depending on which resource (if either) is currently limiting your server.
  • Compared to HTTP/S, SPDY requires fewer Apache worker threads, which increases server capacity. As a result, the server may attract more SPDY traffic.

From these results, it's clear that Apache tuning performed for HTTP/S may not be appropriate after SPDY is enabled on the server. It's important to take the time to re-evaluate server sizing and retune the server before you start handling SPDY requests from your users.

As I mentioned earlier, the test results I've shared here are specific to my server configuration and the web page I used for the tests. It's important to understand how your server will perform under a realistic user load before you make SPDY available to the users on your site. I encourage you to test your own server and website using a load testing tool such as NeoLoad (there's a free 30-day trial if you want) to see how SPDY will affect your users' response times and your server's performance.

More Stories By Hervé Servy

Hervé Servy is a Senior Performance Engineer at Neotys. He has spent 10 years working for IBM-Rational and Microsoft pre-sales and marketing in France and the Middle East. During the past 3 years, as a personal project, Hervé founded a nonprofit organization in the health 2.0 area. If that isn’t techie enough, Hervé was also born on the very same day Apple Computer was founded.

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.

@ThingsExpo Stories
"People are a lot more knowledgeable about APIs now. There are two types of people who work with APIs - IT people who want to use APIs for something internal and the product managers who want to do something outside APIs for people to connect to them," explained Roberto Medrano, Executive Vice President at SOA Software, in this SYS-CON.tv interview at Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Performance is the intersection of power, agility, control, and choice. If you value performance, and more specifically consistent performance, you need to look beyond simple virtualized compute. Many factors need to be considered to create a truly performant environment. In his General Session at 15th Cloud Expo, Harold Hannon, Sr. Software Architect at SoftLayer, discussed how to take advantage of a multitude of compute options and platform features to make cloud the cornerstone of your online presence.
In this Women in Technology Power Panel at 15th Cloud Expo, moderated by Anne Plese, Senior Consultant, Cloud Product Marketing at Verizon Enterprise, Esmeralda Swartz, CMO at MetraTech; Evelyn de Souza, Data Privacy and Compliance Strategy Leader at Cisco Systems; Seema Jethani, Director of Product Management at Basho Technologies; Victoria Livschitz, CEO of Qubell Inc.; Anne Hungate, Senior Director of Software Quality at DIRECTV, discussed what path they took to find their spot within the technology industry and how do they see opportunities for other women in their area of expertise.
DevOps Summit 2015 New York, 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 widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait for long development cycles that produce software that is obsolete at launch. DevOps may be disruptive, but it is essential.
Wearable devices have come of age. The primary applications of wearables so far have been "the Quantified Self" or the tracking of one's fitness and health status. We propose the evolution of wearables into social and emotional communication devices. Our BE(tm) sensor uses light to visualize the skin conductance response. Our sensors are very inexpensive and can be massively distributed to audiences or groups of any size, in order to gauge reactions to performances, video, or any kind of presentation. In her session at @ThingsExpo, Jocelyn Scheirer, CEO & Founder of Bionolux, will discuss ho...
Almost everyone sees the potential of Internet of Things but how can businesses truly unlock that potential. The key will be in the ability to discover business insight in the midst of an ocean of Big Data generated from billions of embedded devices via Systems of Discover. Businesses will also need to ensure that they can sustain that insight by leveraging the cloud for global reach, scale and elasticity.
“With easy-to-use SDKs for Atmel’s platforms, IoT developers can now reap the benefits of realtime communication, and bypass the security pitfalls and configuration complexities that put IoT deployments at risk,” said Todd Greene, founder & CEO of PubNub. PubNub will team with Atmel at CES 2015 to launch full SDK support for Atmel’s MCU, MPU, and Wireless SoC platforms. Atmel developers now have access to PubNub’s secure Publish/Subscribe messaging with guaranteed ¼ second latencies across PubNub’s 14 global points-of-presence. PubNub delivers secure communication through firewalls, proxy ser...
We’re no longer looking to the future for the IoT wave. It’s no longer a distant dream but a reality that has arrived. It’s now time to make sure the industry is in alignment to meet the IoT growing pains – cooperate and collaborate as well as innovate. In his session at @ThingsExpo, Jim Hunter, Chief Scientist & Technology Evangelist at Greenwave Systems, will examine the key ingredients to IoT success and identify solutions to challenges the industry is facing. The deep industry expertise behind this presentation will provide attendees with a leading edge view of rapidly emerging IoT oppor...
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.
Connected devices and the Internet of Things are getting significant momentum in 2014. In his session at Internet of @ThingsExpo, Jim Hunter, Chief Scientist & Technology Evangelist at Greenwave Systems, examined three key elements that together will drive mass adoption of the IoT before the end of 2015. The first element is the recent advent of robust open source protocols (like AllJoyn and WebRTC) that facilitate M2M communication. The second is broad availability of flexible, cost-effective storage designed to handle the massive surge in back-end data in a world where timely analytics is e...
"There is a natural synchronization between the business models, the IoT is there to support ,” explained Brendan O'Brien, Co-founder and Chief Architect of Aria Systems, in this SYS-CON.tv interview at the 15th International Cloud Expo®, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
The Internet of Things will put IT to its ultimate test by creating infinite new opportunities to digitize products and services, generate and analyze new data to improve customer satisfaction, and discover new ways to gain a competitive advantage across nearly every industry. In order to help corporate business units to capitalize on the rapidly evolving IoT opportunities, IT must stand up to a new set of challenges. In his session at @ThingsExpo, Jeff Kaplan, Managing Director of THINKstrategies, will examine why IT must finally fulfill its role in support of its SBUs or face a new round of...
The BPM world is going through some evolution or changes where traditional business process management solutions really have nowhere to go in terms of development of the road map. In this demo at 15th Cloud Expo, Kyle Hansen, Director of Professional Services at AgilePoint, shows AgilePoint’s unique approach to dealing with this market circumstance by developing a rapid application composition or development framework.
The Internet of Things will greatly expand the opportunities for data collection and new business models driven off of that data. In her session at @ThingsExpo, Esmeralda Swartz, CMO of MetraTech, discussed how for this to be effective you not only need to have infrastructure and operational models capable of utilizing this new phenomenon, but increasingly service providers will need to convince a skeptical public to participate. Get ready to show them the money!

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 platform-as-a-service. The new platform enables developers to build ap...

Building low-cost wearable devices can enhance the quality of our lives. In his session at Internet of @ThingsExpo, Sai Yamanoor, Embedded Software Engineer at Altschool, provided an example of putting together a small keychain within a $50 budget that educates the user about the air quality in their surroundings. He also provided examples such as building a wearable device that provides transit or recreational information. He then reviewed the resources available to build wearable devices at home including open source hardware, the raw materials required and the options available to power s...
The Internet of Things is not new. Historically, smart businesses have used its basic concept of leveraging data to drive better decision making and have capitalized on those insights to realize additional revenue opportunities. So, what has changed to make the Internet of Things one of the hottest topics in tech? In his session at @ThingsExpo, Chris Gray, Director, Embedded and Internet of Things, discussed the underlying factors that are driving the economics of intelligent systems. Discover how hardware commoditization, the ubiquitous nature of connectivity, and the emergence of Big Data a...
The Internet of Things promises to transform businesses (and lives), but navigating the business and technical path to success can be difficult to understand. In his session at @ThingsExpo, Sean Lorenz, Technical Product Manager for Xively at LogMeIn, demonstrated how to approach creating broadly successful connected customer solutions using real world business transformation studies including New England BioLabs and more.
We certainly live in interesting technological times. And no more interesting than the current competing IoT standards for connectivity. Various standards bodies, approaches, and ecosystems are vying for mindshare and positioning for a competitive edge. It is clear that when the dust settles, we will have new protocols, evolved protocols, that will change the way we interact with devices and infrastructure. We will also have evolved web protocols, like HTTP/2, that will be changing the very core of our infrastructures. At the same time, we have old approaches made new again like micro-services...
Enthusiasm for the Internet of Things has reached an all-time high. In 2013 alone, venture capitalists spent more than $1 billion dollars investing in the IoT space. With "smart" appliances and devices, IoT covers wearable smart devices, cloud services to hardware companies. Nest, a Google company, detects temperatures inside homes and automatically adjusts it by tracking its user's habit. These technologies are quickly developing and with it come challenges such as bridging infrastructure gaps, abiding by privacy concerns and making the concept a reality. These challenges can't be addressed w...