Building Scalable eBusiness Solutions with ArsDigita

by Bryan Che (bryanche@arsdigita.com), Tracy Adams (teadams@arsdigita.com), Bruce Keilin (brucek@arsdigita.com)

Submitted on: 2001-03-08
Last updated: 2001-04-25

ArsDigita : ArsDigita Systems Journal : One article

Overview

A successful eBusiness service solution must not only meet the functional business requirements that define its client's needs but also scale reliably and economically to meet the demand for that service.

Two important elements in providing a scalable system are:

By extending a scalable software base, the ArsDigita Community System (ACS), and deploying a scalable hardware architecture, ArsDigita-built solutions are able to realize throughput and performance gains without requiring custom software changes.

ArsDigita-built Web sites, based on the ACS, have been proven and tested to support exceptional performance of up to 49 page views per second, or a rate of 4.23 million page views per day, with a download time averaging less than 4 seconds. ArsDigita produced these results for a client Web site using 500 simultaneous users, with each user waiting five seconds between page requests. The virtual users followed traffic patterns based on actual server logs from the production Web server. The tested hardware configuration was one eight-CPU Sun E4500 with eight GB of RAM as the database server and four one-CPU Sun Netras, each with 256 MB of RAM, as the Web servers. Adding more hardware could further increase the performance of the tested Web site.

The ArsDigita scaling lab runs performance tests, and it benchmarks both the ACS and ACS-based sites against client-specified load requirements. This facility provides ArsDigita with the ability to determine hardware requirements for deployment and also to proactively discover and address performance and scalability bottlenecks well before they reach production.

Production Examples

Photo.net (http://photo.net), running on one Sun E450 with four CPU's, four GB of RAM, four mirrored 17-GB RAID and one mirrored eight-GB RAID, achieves the following performance: Other example Web sites include the following:

Scalability Testing

ArsDigita maintains a scaling lab in its Cambridge headquarters. It uses this lab to help continually build up scaling knowledge and improve the ACS. ArsDigita offers a scaling service using this lab to identify hardware requirements for client's particular needs. By testing Web sites in this lab, ArsDigita is able to:

Scalability Results

With four Sun Netras (one CPU, 256MB RAM) as Web servers, one Netra serving images and one Sun e4500 (eight CPU's, eight GB of RAM) database server, ArsDigita scaled one of its sites to a throughput of 49 pages per second, or a rate of 4.23 million pages per day. The results are shown in the two figures below. The full report is available as a sample scaling document.

ArsDigita simulated 500 simultaneous users cycling through scripts that represented typical behavior on the tested site. It based the simulated traffic pattern on actual server logs from the production site. ArsDigita used a delay of five seconds between each requested page in order to simulate real user behavior as they stop to read pages on the site.

Figure 1 depicts the average page load time of the site's core pages with an increasing number of simulated users. The vast majority of the pages were served in less than an average of four seconds (beating industry standards), even at 500 simulated-users. The second figure shows the number of page-views per second the system was able to achieve.

Figure 1 Sample Performance Vs Users Chart

Figure 2 Sample Throughput Chart

Benchmarks for ACS Java 4.0 show that it performs better than the ACS TCL/AOLserver architecture. As the data model and queries for both ACS Java and ACS Tcl are the same, this improvement is due to better performance in the scripting layer. Using Apache Bench and a single four-CPU E450, ArsDigita measured the peak throughput of certain ACS pages:

Page ACS Java/Resin 1.21
(page views/sec) 		TCL/AOLserver 3.2
(page views/sec)
Empty loop (100 iterations) 50.14 24.08
/index (default root page) 38.02 11.52
/shared/community-member 14.40 5.55

Table 1 Java Vs Tcl Results

Technical Review

Hardware Scaling Strategy

A client site's hardware setup will depend on the customer's application, traffic and performance requirements. ArsDigita designed its hardware architecture, though, so that any site can readily support more traffic by simply adding more, inexpensive hardware.

Figure 3 ArsDigita Hardware Setup

Database server(s): ArsDigita typically dedicates an enterprise-class server such as a Sun e420 to run the RDBMS. These servers have four CPU's and up to four GB RAM. ArsDigita recommends a kind of server to use as a Web site's database server based upon the level of information processing the database must perform. With proper capacity planning, the recommended database server should prove sufficient for a long time.

If Web site traffic should increase to the point that the site requires a faster RDBMS server, ArsDigita can swap in a more powerful machine for the existing database server. If a single powerful server such as a Sun E4500 or E10000 becomes fully utilized, ArsDigita may employ other, more complicated scaling options such as clustering using Oracle Parallel .

Web Servers: ArsDigita runs its Web servers and application code on a number of small, relatively inexpensive machines. These front-end machines, typically Sun Netras or VA Linux machines, run identical copies of a site's Web server and application. By distributing its load across multiple machines, ArsDigita is able to achieve cheap and reasonable hardware scalability as well as reliability. ArsDigita can add additional Web servers to grow the Web site's capacity as needed.

Load balancers: A load balancer receives all of a Web site's incoming traffic and then distributes this traffic among the Web site's front-end Web servers. ArsDigita uses its load balancers to help ensure that no individual Web server becomes overwhelmed and to partition the work to different Web services. The load balancer also provides a level of fault tolerance by frequently monitoring the status of the Web servers and removing any that are slow or non-responsive from the available server pool.

More Information:

Software components

ArsDigita builds its custom Web sites using the following software components:

Figure 4 Software Component Stack

Additional Information

ArsDigita's scaling lab has written a document, ArsDigita Scalability Testing, detailing its methodologies for evaluating a Web site's scalability. ArsDigita also may provide sample scalability reports it has written for some of its clients and WebTrends data from photo.net.
asj-editors@arsdigita.com

Reader's Comments

WRT the tcl / java speed comparison chart: are the tcl numbers with nsd7 or nsd8? I've heard that can make a difference.

-- Jonathan Ellis, May 15, 2001
The Tcl tests used nsd8

-- Bryan Che, May 21, 2001

From the bookmarks you say you get 24.08 pageviews for an empty 100 iteration loop page on a 4-cpu e450 with tcl/aol3.2? Why such poor performance? Is it the overhead due to filters you have registered? On my measly pIII 550 I get over 60 page/sec from ab while running other background processes as well?



-- Carl Garland, May 24, 2001
/index does little but call the RDBMS then return a template. Are you certain that you're not just measuring the difference between the two templating implementations? The fact that Java can iterate faster than Tcl is neither surprising nor terrible relevant.

Most of the time consumed in serving ACS 4 Tcl pages seem to be spent in the request processor, the RDBMS, and the template system. Pinning the problem on the scripting language per se without further analyis doesn't really seem warranted.



-- Don Baccus, May 28, 2001

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