|By Gary Kaiser||
|July 9, 2014 07:45 AM EDT||
When we think of application performance problems that are network-related, we often immediately think of bandwidth and congestion as likely culprits; faster speeds and less traffic will solve everything, right? This is reminiscent of recent ISP wars; which is better, DSL or cable modems? Cable modem proponents touted the higher bandwidth while DSL proponents warned of the dangers of sharing the network with your potentially bandwidth-hogging neighbors. In this blog entry, we'll examine these two closely-related constraints, beginning the series of performance analyses using the framework we introduced in Part I. I'll use graphics from Compuware's application-centric protocol analyzer - Transaction Trace - as illustrations.
We define bandwidth delay as the serialization delay encountered as bits are clocked out onto the network medium. Most important for performance analysis is what we refer to as the "bottleneck bandwidth" - the speed of the link at its slowest point - as this will be the primary influencer on the packet arrival rate at the destination. Each packet incurs the serialization delay dictated by the link speed; for example, at 4Mbps, a 1500 byte packet takes approximately 3 milliseconds to be serialized. Extending this bandwidth calculation to an entire operation is relatively straightforward. We observe (on the wire) the number of bytes sent or received and multiply that by 8 bits, then divide by the bottleneck link speed, understanding that asymmetric links may have different upstream and downstream speeds.
Bandwidth effect = [ [# bytes sent or received] x [8 bits] ]/ [Bottleneck link speed]
For example, we can calculate the bandwidth effect for an operation that sends 100KB and receives 1024KB on a 2048Kbps link:
- Upstream effect: [100,000 * 8] / 2,048,000] = 390 milliseconds
- Downstream effect: [1,024,000 *8] / 2,048,000] = 4000 milliseconds
For better precision, you should account for frame header size differences between the packet capture medium - Ethernet, likely - and the WAN link; this difference might be as much as 8 or 10 bytes per packet.
Bandwidth constraints impact only the data transfer periods within an operation - the request and reply flows. Each flow also incurs (at a minimum) additional delay due to network latency, as the first bit traverses the network from sender to receiver; TCP flow control or other factors may introduce further delays. (As an operation's chattiness increases, its sensitivity to network latency increases and the overall impact of bandwidth tends to decrease, becoming overshadowed by latency.)
Transaction Trace Illustration: Bandwidth
One way to frame the question is "does the operation use all of the available bandwidth?" The simplest way to visualize this is to graph throughput in each direction, comparing uni-directional throughput with the link's measured bandwidth. If the answer is yes, then the operation bottleneck is bandwidth; if the answer is no, then there is some other constraint limiting performance. (This doesn't mean that bandwidth isn't a significant, or even the dominant, constraint; it simply means that there are other factors that prevent the operation from reaching the bandwidth limitation. The formula we used to calculate the impact of bandwidth still applies as a definition of the contribution of bandwidth to the overall operation time.)
This FTP transfer is frequently limited by the 10Mbps available bandwidth.
Networks are generally shared resources; when there are multiple connections on a link, TCP flow control will prevent a single flow from using all of the available bandwidth as it detects and adjusts for congestion. We will evaluate the impact of congestion next, but fundamentally, the diagnosis is the same; bandwidth constrains throughput.
Congestion occurs when data arrives at a network interface at a rate faster than the media can service; when this occurs, packets must be placed in an output queue, waiting until earlier packets have been serviced. These queue delays add to the end-to-end network delay, with a potentially significant effect on both chatty and non-chatty operations. (Chatty operations will be impacted due to the increase in round-trip delay, while non-chatty operations may be impacted by TCP flow control and congestion avoidance algorithms.)
For a given flow, congestion initially reduces the rate of TCP slow-start's ramp by slowing increases to the sender's Congestion Window (CWD); it also adds to the delay component of the Bandwidth Delay Product (BDP), increasing the likelihood of exhausting the receiver's TCP window. (We'll discuss TCP slow-start as well as the BDP later in this series.)
As congestion becomes more severe, the queue in one of the path's routers may become full. As packets arrive exceeding the queue's storage capacity, some packets must be discarded. Routers employ various algorithms to determine which packets should be dropped, perhaps attempting to distribute congestion's impact among multiple connections, or to more significantly impact lower-priority traffic. When TCP detects these dropped packets (by a triple-duplicate ACK, for example), congestion is the assumed cause. As we will discuss in more depth in an upcoming blog entry, packet loss causes the sending TCP to reduce its Congestion Window by 50%, after which slow-start begins to ramp up again in a relatively conservative congestion avoidance phase.
For more on congestion, and for further insight, click here for the full article.
Organizations already struggle with the simple collection of data resulting from the proliferation of IoT, lacking the right infrastructure to manage it. They can't only rely on the cloud to collect and utilize this data because many applications still require dedicated infrastructure for security, redundancy, performance, etc. In his session at 17th Cloud Expo, Emil Sayegh, CEO of Codero Hosting, will discuss how in order to resolve the inherent issues, companies need to combine dedicated a...
Oct. 4, 2015 12:00 AM EDT Reads: 362
Clearly the way forward is to move to cloud be it bare metal, VMs or containers. One aspect of the current public clouds that is slowing this cloud migration is cloud lock-in. Every cloud vendor is trying to make it very difficult to move out once a customer has chosen their cloud. In his session at 17th Cloud Expo, Naveen Nimmu, CEO of Clouber, Inc., will advocate that making the inter-cloud migration as simple as changing airlines would help the entire industry to quickly adopt the cloud wit...
Oct. 3, 2015 09:00 PM EDT Reads: 339
SYS-CON Events announced today that VividCortex, the monitoring solution for the modern data system, will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. The database is the heart of most applications, but it’s also the part that’s hardest to scale, monitor, and optimize even as it’s growing 50% year over year. VividCortex is the first unified suite of database monitoring tools specifically desi...
Oct. 3, 2015 05:00 PM EDT Reads: 305
Apps and devices shouldn't stop working when there's limited or no network connectivity. Learn how to bring data stored in a cloud database to the edge of the network (and back again) whenever an Internet connection is available. In his session at 17th Cloud Expo, Bradley Holt, Developer Advocate at IBM Cloud Data Services, will demonstrate techniques for replicating cloud databases with devices in order to build offline-first mobile or Internet of Things (IoT) apps that can provide a better, ...
Oct. 3, 2015 05:00 PM EDT Reads: 312
SYS-CON Events announced today that Cloud Raxak has been named “Media & Session Sponsor” of SYS-CON's 17th Cloud Expo, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Raxak Protect automates security compliance across private and public clouds. Using the SaaS tool or managed service, developers can deploy cloud apps quickly, cost-effectively, and without error.
Oct. 3, 2015 01:15 PM EDT Reads: 558
SYS-CON Events announced today that ProfitBricks, the provider of painless cloud infrastructure, will exhibit at SYS-CON's 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. ProfitBricks is the IaaS provider that offers a painless cloud experience for all IT users, with no learning curve. ProfitBricks boasts flexible cloud servers and networking, an integrated Data Center Designer tool for visual control over the...
Oct. 3, 2015 01:00 PM EDT Reads: 641
SYS-CON Events announced today that IBM Cloud Data Services has been named “Bronze Sponsor” of SYS-CON's 17th Cloud Expo, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. IBM Cloud Data Services offers a portfolio of integrated, best-of-breed cloud data services for developers focused on mobile computing and analytics use cases.
Oct. 3, 2015 12:00 PM EDT Reads: 360
Learn how IoT, cloud, social networks and last but not least, humans, can be integrated into a seamless integration of cooperative organisms both cybernetic and biological. This has been enabled by recent advances in IoT device capabilities, messaging frameworks, presence and collaboration services, where devices can share information and make independent and human assisted decisions based upon social status from other entities. In his session at @ThingsExpo, Michael Heydt, founder of Seamless...
Oct. 3, 2015 11:00 AM EDT Reads: 580
In recent years, at least 40% of companies using cloud applications have experienced data loss. One of the best prevention against cloud data loss is backing up your cloud data. In his General Session at 17th Cloud Expo, Bryan Forrester, Senior Vice President of Sales at eFolder, will present how organizations can use eFolder Cloudfinder to automate backups of cloud application data. He will also demonstrate how easy it is to search and restore cloud application data using Cloudfinder.
Oct. 3, 2015 10:15 AM EDT Reads: 257
Docker is hot. However, as Docker container use spreads into more mature production pipelines, there can be issues about control of Docker images to ensure they are production-ready. Is a promotion-based model appropriate to control and track the flow of Docker images from development to production? In his session at DevOps Summit, Fred Simon, Co-founder and Chief Architect of JFrog, will demonstrate how to implement a promotion model for Docker images using a binary repository, and then show h...
Oct. 3, 2015 10:00 AM EDT Reads: 612
Redis is not only the fastest database, but it has become the most popular among the new wave of applications running in containers. Redis speeds up just about every data interaction between your users or operational systems. In his session at 17th Cloud Expo, Dave Nielsen, Developer Relations at Redis Labs, will share the functions and data structures used to solve everyday use cases that are driving Redis' popularity
Oct. 3, 2015 10:00 AM EDT Reads: 190
You have your devices and your data, but what about the rest of your Internet of Things story? Two popular classes of technologies that nicely handle the Big Data analytics for Internet of Things are Apache Hadoop and NoSQL. Hadoop is designed for parallelizing analytical work across many servers and is ideal for the massive data volumes you create with IoT devices. NoSQL databases such as Apache HBase are ideal for storing and retrieving IoT data as “time series data.”
Oct. 3, 2015 09:45 AM EDT Reads: 308
SYS-CON Events announced today that HPM Networks will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. For 20 years, HPM Networks has been integrating technology solutions that solve complex business challenges. HPM Networks has designed solutions for both SMB and enterprise customers throughout the San Francisco Bay Area.
Oct. 3, 2015 09:00 AM EDT Reads: 487
SYS-CON Events announced today that DataClear Inc. will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. The DataClear ‘BlackBox’ is the only solution that moves your PC, browsing and data out of the United States and away from prying (and spying) eyes. Its solution automatically builds you a clean, on-demand, virus free, new virtual cloud based PC outside of the United States, and wipes it clean...
Oct. 3, 2015 09:00 AM EDT Reads: 509
Mobile, social, Big Data, and cloud have fundamentally changed the way we live. “Anytime, anywhere” access to data and information is no longer a luxury; it’s a requirement, in both our personal and professional lives. For IT organizations, this means pressure has never been greater to deliver meaningful services to the business and customers.
Oct. 3, 2015 09:00 AM EDT Reads: 240
SYS-CON Events announced today that Machkey International Company will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Machkey provides advanced connectivity solutions for just about everyone. Businesses or individuals, Machkey is dedicated to provide high-quality and cost-effective products to meet all your needs.
Oct. 3, 2015 08:00 AM EDT Reads: 225
DevOps is speeding towards the IT world like a freight train and the hype around it is deafening. There is no reason to be afraid of this change as it is the natural reaction to the agile movement that revolutionized development just a few years ago. By definition, DevOps is the natural alignment of IT performance to business profitability. The relevance of this has yet to be quantified but it has been suggested that the route to the CEO’s chair will come from the IT leaders that successfully ma...
Oct. 3, 2015 06:00 AM EDT Reads: 14,005
The broad selection of hardware, the rapid evolution of operating systems and the time-to-market for mobile apps has been so rapid that new challenges for developers and engineers arise every day. Security, testing, hosting, and other metrics have to be considered through the process. In his session at Big Data Expo, Walter Maguire, Chief Field Technologist, HP Big Data Group, at Hewlett-Packard, will discuss the challenges faced by developers and a composite Big Data applications builder, foc...
Oct. 3, 2015 04:00 AM EDT Reads: 281
As enterprises capture more and more data of all types – structured, semi-structured, and unstructured – data discovery requirements for business intelligence (BI), Big Data, and predictive analytics initiatives grow more complex. A company’s ability to become data-driven and compete on analytics depends on the speed with which it can provision their analytics applications with all relevant information. The task of finding data has traditionally resided with IT, but now organizations increasingl...
Oct. 3, 2015 04:00 AM EDT Reads: 303
SYS-CON Events announced today that MobiDev, a software development company, will exhibit at the 17th International Cloud Expo®, which will take place November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. MobiDev is a software development company with representative offices in Atlanta (US), Sheffield (UK) and Würzburg (Germany); and development centers in Ukraine. Since 2009 it has grown from a small group of passionate engineers and business managers to a full-scale mobi...
Oct. 3, 2015 03:00 AM EDT Reads: 634