David Cancel and I have had sort of a passing vague, same space and thought process, living in the same Metropolitan area kind of distant acquaintance for about the same year.

About 2-3 months ago, he wrote a pair of articles discussing the efforts he has undertaken in order to try and offload some of the traffic to the servers for his new company, Lookery. While they are not current, in the sense that time moves in one direction for most technical people, and is compressed into the events of the past eight hours and the next 30 minutes, these articles provide an insight that should not be missed.

These two articles show how easily a growing company that is trying to improve performance and customer experience can achieve measureable results on a budget that consists of can recycling money and green stamps.

Measuring your CDN

A service that relies on the request and downloading of a single file from a single location very quickly realizes the limitations that this model imposes as traffic begins to broaden and increase. Geographically diverse users begin to notice performance delays as they attempt to reach a single, geographically-specific server. And the hosting location, even one as large as Amazon S3, can begin to serve as the bottleneck to success.

David’s first article examines the solution path that Lookery chose, which was moving the tag, which drives the entire opportunity for success in their business model, onto a CDN. With a somewhat enigmatic title (Using Amazon S3 as a CDN?), he describes how the Lookery team measured the distributed performance of their JS tag using a free measurement service (not GrabPERF) and compared various CDNs against the origin configuration that is based on the Amazon S3 environment.

This deceptively simple test, which is perfect for the type of system that Lookery uses, provided that team with the data they needed to realize that they had made a good choice in choosing a CDN and that their chosen CDN was able to deliver improved response times when compared to their origin servers.

Check your Cacheability

Cacheability is a nasty word that my spell-checker hates. To define it simply, it refers to the ability of end-user browsers and network-level caching proxies to store and re-use downloaded content based on clear and explicit caching rules delivered in the server response header.

The second Article in David’s series describes how, using Mark Nottingham’s Cacheability Engine, the Lookery team was able to examine the way that the CDNs and the Origin site informed the visitor browser of the cacheability of the JS file that they were downloading.

Cacheability doesn’t seem that important until you remember that most small firms are very conscious of the Bandwidth outlay. These small startups arevery aware when their bandwidth usage reaches 250GB/month level (Lookery’s bandwidth usage at the time the posts were written). Any method that can improve end-user performance while stilll delivering the service they expect is a welcome addition, especially when it is low-cost to free.

In the post, David notes that there appears to be no way in their chosen CDN to modify the Cacheability settings, an issue which appears to have been remedied since the article went up [See current server response headers for the Lookery tag here].

Conclusion

Startups spend a lot of time imagining what success looks like. And when it comes, sometimes they aren’t ready for it, especially when it comes to the ability to handle increasing loads with their often centralized, single-location architectures.

David Cancel, in these two articles, shows how a little early planning, some clear goals, and targeted performance measurement can provide an organization with the information to get them through their initial growth spurt in style.

This paper is an extension of the work done for another article that highlighted the performance benefits of retrieving uncompressed and compressed objects directly from the origin server. I wanted to add a proxy server into the stream and determine if proxy servers helped improve the performance of object downloads, and by how much.

Using the same series of objects in the original compression article[1], the CURL tests were re-run 3 times:

1. Directly from the origin server
2. Through the proxy server, to load the files into cache
3. Through the proxy server, to avoid retrieving files from the origin.[2]

This series of three tests was repeated twice: once for the uncompressed files, and then for the compressed objects.[3]

As can be seen clearly in the plots below, compression caused web page download times to improve greatly, when the objects were retrieved from the source. However, the performance difference between compressed and uncompressed data all but disappears when retrieving objects from a proxy server on a corporate LAN.

Instead of the linear growth between object size and download time seen in both of the retrieval tests that used the origin server (Source and Proxy Load data), the Proxy Draw data clearly shows the benefits that accrue when a proxy server is added to a network to assist with serving HTTP traffic.

	MEAN DOWNLOAD TIME
Uncompressed Pages
Total Time Uncompressed — No Proxy	0.256
Total Time Uncompressed — Proxy Load	0.254
Total Time Uncompressed — Proxy Draw	0.110
Compressed Pages
Total Time Compressed — No Proxy	0.181
Total Time Compressed — Proxy Load	0.140
Total Time Compressed — Proxy Draw	0.104

The data above shows just how much of an improvement is gained by adding a local proxy server, explicit caching descriptions and compression can add to a Web site. For sites that do force a great of requests to be returned directly to the origin server, compression will be of great help in reducing bandwidth costs and improving performance. However, by allowing pages to be cached in local proxy servers, the difference between compressed and uncompressed pages vanishes.

Conclusion

Compression is a very good start when attempting to optimize performance. The addition of explicit caching messages in server responses which allow proxy servers to serve cached data to clients on remote local LANs can improve performance to even a greater extent than compression can. These two should be used together to improve the overall performance of Web sites.

[1]The test set was made up of the 1952 HTML files located in the top directory of the Linux Documentation Project HTML archive.

[2]All of the pages in these tests announced the following server response header indicating its cacheability:

Cache-Control: max-age=3600

[3]A note on the compressed files: all compression was performed dynamically by mod_gzip for Apache/1.3.27.

This paper is an extension of the work done for another article that highlighted the performance benefits of retrieving uncompressed and compressed objects directly from the origin server. I wanted to add a proxy server into the stream and determine if proxy servers helped improve the performance of object downloads, and by how much.

Using the same series of objects in the original compression article^[1], the CURL tests were re-run 3 times:

1. Directly from the origin server
2. Through the proxy server, to load the files into cache
3. Through the proxy server, to avoid retrieving files from the origin.^[2]

eries of three tests was repeated twice: once for the uncompressed files, and then for the compressed objects.^[3]

As can be seen clearly in the plots below, compression caused web page download times to improve greatly, when the objects were retrieved from the source. However, the performance difference between compressed and uncompressed data all but disappears when retrieving objects from a proxy server on a corporate LAN.

Instead of the linear growth between object size and download time seen in both of the retrieval tests that used the origin server (Source and Proxy Load data), the Proxy Draw data clearly shows the benefits that accrue when a proxy server is added to a network to assist with serving HTTP traffic.

Uncompressed Pages

	MEAN DOWNLOAD TIME
Total Time Uncompressed — No Proxy	0.256
Total Time Uncompressed — Proxy Load	0.254
Total Time Uncompressed — Proxy Draw	0.110

Compressed Pages

Total Time Compressed — No Proxy	0.181
Total Time Compressed — Proxy Load	0.140
Total Time Compressed — Proxy Draw	0.104

The data above shows just how much of an improvement is gained by adding a local proxy server, explicit caching descriptions and compression can add to a Web site. For sites that do force a great of requests to be returned directly to the origin server, compression will be of great help in reducing bandwidth costs and improving performance. However, by allowing pages to be cached in local proxy servers, the difference between compressed and uncompressed pages vanishes.

Conclusion

Compression is a very good start when attempting to optimize performance. The addition of explicit caching messages in server responses which allow proxy servers to serve cached data to clients on remote local LANs can improve performance to even a greater extent than compression can. These two should be used together to improve the overall performance of Web sites.

[1] The test set was made up of the 1952 HTML files located in the top directory of the Linux Documentation Project HTML archive.

[2] All of the pages in these tests announced the following server response header indicating its cacheability: Cache-Control: max-age=3600

[3] A note on the compressed files: all compression was performed dynamically by mod_gzip for Apache/1.3.27.

Got an e-mail from the team at Port80 Software in San Diego. They have a compression and caching solution for IIS, which although not my development platform of choice, is heavily used in the Fortune 1000, mainly due to the requirement from these firms to contract with a vendor with enterprise support programs.

The link below takes you to their variety of tools that check the cacheability and compressibility (this a word?) of your pages.

Port80 Tools Page

They also have a blog — [200 OK]. Drop by and check them out — there is a very interesting discussion on TIME_WAIT states going on, an oft-forgotten little tweak that is available for high-performance Web servers.