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Q: This seems like an awful lot of work. Is it really worth it?
A: Yes! And not just for your AvantGo channel. There are many ISPs out there that take advantage of caching as well. Once you have set up your channel for caching, go and set up the rest of your site for caching. Your website will suddenly seem to download a whole lot faster. So it is definitely worth the time.
Q: I set up my front page's logo to expire in several months. Now they are telling us we have a new logo. How do I change it?
A: Once a file has been cached, there is not a whole lot you can do to change it. What you can do, however, is create a new file for your logo and have your front page point to version 2 of the logo instead. Once your front page expires (which should be significantly less than 6 months), the new version that points to the new logo will be used.
For this reason, we recommend that if you are just testing your channel, you keep it all non-cached before it goes live.
Q: Hey, I set up my channel for caching, but I am still getting thousands of hits a day! What is wrong?
A: Nothing is wrong. Remember that we have several sync servers, each with its own cache, and we cache different versions for different devices. You might reasonably expect a single page to be hit 50 to 60 times per caching period before it is finally cached in every form on every sync server. This means that if you have a channel with 20 pages, your server could still get hit 1000 times by AvantGo sync servers for every cache period.
Q: It seems like that would defeat the purpose of caching?
A: No. Remember, that is pretty much an upper limit to how often your page will get hit. That is, if your subscriber numbers doubled, your server would still only get hit about 1000 times by AvantGo sync servers. If you want to reduce your page hits even more, increase your caching time.
Q: How can I tell I have set caching up properly?
A: The easiest way is check your HTTP headers. Telnet to your website using port 80 and retrieve the page using a Look at the headers that get returned. If you see the Those of you who work in Unix-based systems might also have the Using a command like the one below will only display your HTTP headers, without any HTML content:
Another way to test caching is to try syncing your channel several times in a row. You should notice your sync gets faster after syncing a few times. (In order to test this, you should only be syncing the channel you are testing. The presence of other channels will hide your results. Also, for testing purposes, you do want the Refresh setting for this channel in your AvantGo account to be set to Every sync.)
A third way is to check out the Cacheability Engine at:
http://www.mnot.net/cacheability/
Follow either of the two links in the "As a public web Engine" section. These will bring you to websites that will report on any URL you would like for basic cacheability. Keep in mind their results are geared for general proxy servers, not the AvantGo sync server, but they should be a fairly accurate guideline.
Finally, if you load your page in Netscape and select View|Page Info you can sometimes tell if your page is set up for caching because a date will appear in the Expires field down below. Note, though, that this is not always accurate. Sometimes you have to unload Netscape's Memory and Disc Cache, and then hit Reload. So do not trust this one too much.
Q: Where can I find more information on caching?
A: There is an excellent tutorial at:
http://www.mnot.net/cache_docs/
Also, for the latest news and juicy gossip about the caching community, be sure to check out:
Q: I like to analyze traffic on my web server, because then I can see how often my pages are being accessed. If I start caching documents on the AvantGo sync server, I will not get the hits on my web server. Is there anything I can do?
A: Well, in all honesty, this is a pretty inaccurate way of figuring out your web traffic. Remember that the AvantGo sync server updates all pages in all channels every time you sync. This means whether a user a) Reads your entire channel, b) Skims the front page, or c) Ignores your channel entirely, every page in your channel is going to get hit once the next time he syncs his mobile device.
If you absolutely must keep track of hits on your site, one trick many people do is to include a transparent 1x1 .gif file that does not cache (using, say, a Q: It seems like this would just move the bottleneck from my web server to your server?
A: No. Remember that people have to hit the AvantGo sync server whether your page is cached or not. The only difference is that if your web page is not cached, our server has to go out and retrieve it, compress it, and then upload it. Whereas if your web page is cached, our server only needs to upload the pre-compressed version. So caching your pages helps us, too.
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